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Carbohydrate
Lactose is a disaccharide found in milk. It consists of
a molecule of D-galactose and a molecule of D-
glucose bonded by beta-1-4 glycosidic linkage. It has
a formula of C12H22O11.
A carbohydrate is an organic compound that
consists only of carbon,hydrogen, and oxygen,
usually with a hydrogen:oxygen atom ratio of 2:1 (as
in water); in other words, with the empirical
formula Cm(H2O)n. (Some exceptions exist; for
example, deoxyribose, a component of DNA, has the
empirical formula C5H10O4.) Carbohydrates are not
technically hydrates of carbon. Structurally it is more
accurate to view them as polyhydroxy
aldehydes and ketones.
The term is most common in biochemistry, where it
is a synonym ofsaccharide. The carbohydrates
(saccharides) are divided into four chemical
groupings: monosaccharides, disaccharides, oligosac
charides, andpolysaccharides. In general, the
monosaccharides and disaccharides, which are
smaller (lower molecular weight) carbohydrates, are
commonly referred to as sugars.[1] The
word saccharide comes from
the Greekword σάκχαρον (sákkharon), meaning
"sugar". While the scientific nomenclature of
carbohydrates is complex, the names of the
monosaccharides and disaccharides very often end
in the suffix -ose. For example, blood sugar is the
monosaccharide glucose, table sugar is the
disaccharide sucrose, and milk sugar is the
disaccharide lactose (see illustration).
Carbohydrates perform numerous roles in living
organisms. Polysaccharides serve for the storage
of energy (e.g., starch and glycogen), and as
structural components (e.g., cellulose in plants
and chitin in arthropods). The 5-carbon
monosaccharide ribose is an important component
of coenzymes (e.g., ATP, FAD, and NAD) and the
backbone of the genetic molecule known as RNA.
The relateddeoxyribose is a component of DNA.
Saccharides and their derivatives include many other
important biomolecules that play key roles in
the immune system, fertilization,
preventing pathogenesis, blood clotting,
and development.[2]
In food science and in many informal contexts, the
term carbohydrate often means any food that is
particularly rich in the complex
carbohydrate starch (such as cereals, bread,
and pasta) or simple carbohydrates, such
as sugar (found in candy, jams, and desserts).
[edit]Structure
Formerly the name "carbohydrate" was used
in chemistry for any compound with the formula
Cm (H2O) n. Following this definition, some chemists
considered formaldehyde (CH2O) to be the simplest
carbohydrate,[3] while others claimed that title
for glycolaldehyde.[4]Today the term is generally
understood in the biochemistry sense, which
excludes compounds with only one or two carbons.
Natural saccharides are generally built of simple
carbohydrates called monosaccharides with general
formula (CH2O)n where n is three or more. A typical
monosaccharide has the structure H-(CHOH)x(C=O)-
(CHOH)y-H, that is, an aldehyde or ketone with
many hydroxylgroups added, usually one on
each carbon atom that is not part of the aldehyde or
ketone functional group. Examples of
monosaccharides are glucose, fructose,
and glyceraldehydes. However, some biological
substances commonly called "monosaccharides" do
not conform to this formula (e.g., uronic acids and
deoxy-sugars such as fucose), and there are many
chemicals that do conform to this formula but are
not considered to be monosaccharides (e.g.,
formaldehyde CH2O and inositol (CH2O)6).[5]
The open-chain form of a monosaccharide often
coexists with a closed ring form where
the aldehyde/ketone carbonyl group carbon (C=O)
and hydroxyl group (-OH) react forming
a hemiacetal with a new C-O-C bridge.
Monosaccharides can be linked together into what
are called polysaccharides (or oligosaccharides) in a
large variety of ways. Many carbohydrates contain
one or more modified monosaccharide units that
have had one or more groups replaced or removed.
For example, deoxyribose, a component of DNA, is a
modified version of ribose; chitin is composed of
repeating units of N-acetyl glucosamine, a nitrogen-
containing form of glucose.
[edit]Monosaccharides
Monosaccharide
D-glucose is an aldohexose with the formula
(C·H2O)6. The red atoms highlight thealdehyde group,
and the blue atoms highlight theasymmetric
centerfurthest from the aldehyde; because this -OH
is on the right of theFischer projection, this is a D
sugar.
Monosaccharides are the simplest carbohydrates in
that they cannot be hydrolyzed to smaller
carbohydrates. They are aldehydes or ketones with
two or more hydroxyl groups. The general chemical
formula of an unmodified monosaccharide is
(C•H2O) n, literally a "carbon hydrate."
Monosaccharides are important fuel molecules as
well as building blocks for nucleic acids. The smallest
monosaccharides, for which n = 3, are
dihydroxyacetone and D- and L-glyceraldehydes.
[edit]Classification of monosaccharides
The α and β anomers of glucose. Note the position of
the hydroxyl group (red or green) on the anomeric
carbon relative to the CH2OH group bound to carbon
5: they are either on the opposite sides (α), or the
same side (β).
Monosaccharides are classified according to three
different characteristics: the placement of
its carbonyl group, the number ofcarbon atoms it
contains, and its chiral handedness. If the carbonyl
group is an aldehyde, the monosaccharide is
an aldose; if the carbonyl group is a ketone, the
monosaccharide is a ketose. Monosaccharides with
three carbon atoms are called trioses, those with
four are calledtetroses, five are called pentoses, six
are hexoses, and so on.[6] These two systems of
classification are often combined. For
example, glucoseis an aldohexose (a six-carbon
aldehyde), ribose is an aldopentose (a five-carbon
aldehyde), and fructose is a ketohexose (a six-carbon
ketone).
Each carbon atom bearing a hydroxyl group (-OH),
with the exception of the first and last carbons,
are asymmetric, making them stereo centerswith
two possible configurations each (R or S). Because of
this asymmetry, a number of isomers may exist for
any given monosaccharide formula. The aldohexose
D-glucose, for example, has the formula (C·H2O) 6, of
which all but two of its six carbons atoms are
stereogenic, making D-glucose one of 24 = 16
possible stereoisomers. In the case
of glyceraldehydes, an aldotriose, there is one pair of
possible stereoisomers, which
are enantiomers and epimers. 1, 3-
dihydroxyacetone, the ketose corresponding to the
aldose glyceraldehydes, is a symmetric molecule
with no stereo centers). The assignment of D or L is
made according to the orientation of the asymmetric
carbon furthest from the carbonyl group: in a
standard Fischer projection if the hydroxyl group is
on the right the molecule is a D sugar, otherwise it is
an L sugar. The "D-" and "L-" prefixes should not be
confused with "d-" or "l-", which indicate the
direction that the sugarrotates plane polarized light.
This usage of "d-" and "l-" is no longer followed in
carbohydrate chemistry.[7]
[edit]Ring-straight chain isomerism
Glucose can exist in both a straight-chain and ring
form.
The aldehyde or ketone group of a straight-chain
monosaccharide will react reversibly with a hydroxyl
group on a different carbon atom to form
a hemiacetal or hemiketal, forming
aheterocyclic ring with an oxygen bridge between
two carbon atoms. Rings with five and six atoms are
called furanose and pyranose forms, respectively,
and exist in equilibrium with the straight-chain form.[8]
During the conversion from straight-chain form to
the cyclic form, the carbon atom containing the
carbonyl oxygen, called the anomeric carbon,
becomes a stereogenic center with two possible
configurations: The oxygen atom may take a position
either above or below the plane of the ring. The
resulting possible pair of stereoisomers is
called anomers. In the α anomer, the -OH
substituent on the anomeric carbon rests on the
opposite side (trans) of the ring from the CH2OH side
branch. The alternative form, in which the CH2OH
substituent and the anomeric hydroxyl are on the
same side (cis) of the plane of the ring, is called the β
anomer.
[edit]Use in living organisms
Monosaccharides are the major source of fuel
for metabolism, being used both as an energy source
(glucose being the most important in nature) and
in biosynthesis. When monosaccharides are not
immediately needed by many cells they are often
converted to more space-efficient forms,
often polysaccharides. In many animals, including
humans, this storage form is glycogen, especially in
liver and muscle cells. In plants, starch is used for the
same purpose.
[edit]Disaccharides
Sucrose, also known as table sugar, is a common
disaccharide. It is composed of two
monosaccharides: D-glucose (left) and D-
fructose(right).
Main article: Disaccharide
Two joined monosaccharides are called
a disaccharide and these are the simplest
polysaccharides. Examples
include sucrose and lactose. They are composed of
two monosaccharide units bound together by
a covalent bond known as a glycosidic linkageformed
via a dehydration reaction, resulting in the loss of
a hydrogen atom from one monosaccharide and
a hydroxyl group from the other. The formula of
unmodified disaccharides is C12H22O11. Although
there are numerous kinds of disaccharides, a handful
of disaccharides are particularly notable.
Sucrose, pictured to the right, is the most abundant
disaccharide, and the main form in which
carbohydrates are transported in plants. It is
composed of one D-glucosemolecule and one D-
fructose molecule. The systematic name for
sucrose, O-α-D-glucopyranosyl-(1→2)-D-
fructofuranoside, indicates four things:
Its monosaccharides: glucose and fructose
Their ring types: glucose is a pyranose, and
fructose is a furanose
How they are linked together: the oxygen on
carbon number 1 (C1) of α-D-glucose is linked to
the C2 of D-fructose.
The -oside suffix indicates that the anomeric
carbon of both monosaccharides participates in
the glycosidic bond.
Lactose, a disaccharide composed of one D-
galactose molecule and one D-glucose molecule,
occurs naturally in mammalian milk. Thesystematic
name for lactose is O-β-D-galactopyranosyl-(1→4)-D-
glucopyranose. Other notable disaccharides
include maltose (two D-glucoses linked α-1,4) and
cellulobiose (two D-glucoses linked β-1,4).
disaccharides can be classified into two types.They
are reducing and non-reducing disaccahrides if the
functional group is present in bonding with another
sugar unit it is called a reducing disaccharide or
biose.
[edit]Nutrition
Grain products: rich sources of carbohydrates
Foods high in carbohydrate include fruits, sweets,
soft drinks, breads, pastas, beans, potatoes, bran,
rice, and cereals. Carbohydrates are a common
source of energy in living organisms; however, no
carbohydrate is an essential nutrient in humans.[9]
Carbohydrates are not necessary building blocks of
other molecules, and the body can obtain all its
energy from protein and fats.[10][11] The brain and
neurons generally cannot burn fat for energy, but
use glucose or ketones. Humans can synthesize
some glucose (in a set of processes known
as gluconeogenesis) from specific amino acids, from
the glycerolbackbone in triglycerides and in some
cases from fatty acids. Carbohydrate and protein
contain 4 kilocalories per gram, while fats contain 9
kilocalories per gram. In the case of protein, this is
somewhat misleading as only some amino acids are
usable for fuel.
Organisms typically cannot metabolize all types of
carbohydrate to yield energy. Glucose is a nearly
universal and accessible source of calories. Many
organisms also have the ability to metabolize
other monosaccharides and Disaccharides, though
glucose is preferred. InEscherichia coli, for example,
the lac operon will express enzymes for the digestion
of lactose when it is present, but if both lactose and
glucose are present the lac operon is repressed,
resulting in the glucose being used first
(see: Diauxie). Polysaccharides are also common
sources of energy. Many organisms can easily break
down starches into glucose, however, most
organisms cannot metabolize cellulose or other
polysaccharides like chitinand arabinoxylans. These
carbohydrates types can be metabolized by some
bacteria and protists. Ruminants and termites, for
example, use microorganisms to process cellulose.
Even though these complex carbohydrates are not
very digestible, they may comprise important dietary
elements for humans. Called dietary fiber, these
carbohydrates enhance digestion among other
benefits.[12]
Based on the effects on risk of heart disease and
obesity,[13] the Institute of Medicine recommends
that American and Canadian adults get between 45–
65% of dietary energy from carbohydrates.[14] The Food and Agriculture Organization and World
Health Organizationjointly recommend that national
dietary guidelines set a goal of 55–75% of total
energy from carbohydrates, but only 10% directly
from sugars (their term for simple carbohydrates).[15]
[edit]Classification
Historically nutritionists have classified
carbohydrates as either simple or complex.
However, the exact delineation of these categories is
ambiguous. Today, simple carbohydrate typically
refers to monosaccharides and disaccharides and
complex carbohydrate
meanspolysaccharides (and oligosaccharides).
However, the term complex carbohydrate was first
used in slightly different context in the U.S. Senate
Select Committee on Nutrition and Human
Needs publication Dietary Goals for the United
States (1977). In this work, complex carbohydrate
were defined as "fruit, vegetables and whole-grains".[16] Some nutritionists use complex carbohydrate to
refer to any sort of digestible saccharide present in a
whole food, where fiber, vitamins and minerals are
also found (as opposed to processed carbohydrates,
which provide calories but few other nutrients).
Some simple carbohydrates (e.g. fructose) are
digested very slowly, while some complex
carbohydrates (starches), especially if processed,
raise blood sugar rapidly. The speed of digestion is
determined by a variety of factors including which
other nutrients are consumed with the
carbohydrate, how the food is prepared, individual
differences in metabolism, and the chemistry of the
carbohydrate.
The USDA's Dietary Guidelines for Americans
2010 call for moderate- to high-carbohydrate
consumption from a balanced diet that includes six
one-ounce servings of grain foods each day, at least
half from whole grain sources and the rest from
enriched.[17]
The glycemic index (GI) and glycemic load concepts
have been developed to characterize food behavior
during human digestion. They rank carbohydrate-
rich foods based on the rapidity and magnitude of
their effect on blood glucose levels. Glycemic index is
a measure of how quickly food glucose is absorbed,
while glycemic load is a measure of the total
absorbable glucose in foods. The insulin index is a
similar, more recent classification method that ranks
foods based on their effects on blood insulin levels,
which are caused by glucose (or starch) and some
amino acids in food.
Glucose
Glucose is by far the most common carbohydrate and classified as a monosaccharide, an aldose, a hexose, and is a reducing sugar. It is also known as dextrose, because it is dextrorotatory (meaning that as an optical isomer is rotates plane polarized light to the right and also an origin for the D designation.
Glucose is also called blood sugar as it circulates in the blood at a concentration of 65-110 mg/dL (or 65-110 mg/100 ml) of blood.
Glucose is initially synthesized by chlorophyll in plants using carbon dioxide from the air and sunlight as an energy source. Glucose is further converted to starch for storage.
Click for larger image
Ring Structure for Glucose:
Up until now we have been presenting the structure of glucose as a chain. In reality, an aqueous sugar solution contains only 0.02% of the glucose in the chain form, the majority of the structure is in the cyclic chair form.Since carbohydrates contain both alcohol and aldehyde or ketone functional groups, the straight-chain form is easily converted into the chair form - hemiacetal ring structure. Due to the tetrahedral geometry of carbons that ultimately make a 6 membered stable ring , the -OH on carbon #5 is converted into the ether linkage to close the ring with carbon #1. This makes a 6 member ring - five carbons and one oxygen.
Steps in the ring closure (hemiacetal synthesis):1. The electrons on the alcohol oxygen are used to bond the carbon #1 to make an ether (red oxygen atom).2. The hydrogen (green) is transferred to the carbonyl oxygen (green) to make a new alcohol group (green).
The chair structures are always written with the orientation depicted on the left to avoid confusion.
Hemiacetal Functional Group:
Carbon # 1 is now called the anomeric carbon and is the center of a hemiacetal functional group. A carbon that has both an ether oxygen and an alcohol group is a hemiacetal.
Open graphic of hemiacetal in a new window
Click for larger image
Compare Alpha and Beta Glucose in the Chair Structures:
The position of the -OH group on the anomeric carbon (#1) is an important distinction for carbohydrate chemistry.
The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal projection.
The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection.
The alpha and beta label is not applied to any other carbon - only the anomeric carbon, in this case # 1.
Compare Alpha and Beta Glucose- Chime in new window
Compare Alpha and Beta Glucose in the Haworth Structures:
Open graphic of Haworth Structures in a new window
The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the Haworth structure this results in an upward projection.
The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the Haworth structure this also results in a downward projection.
Galactose
Galactose is more commonly found in the disaccharide, lactose or milk sugar. It is found as the monosaccharide in peas.
Galactose is classified as a monosaccharide, an aldose, a hexose, and is a reducing sugar.
Galactosemia - Genetic Enzyme Deficiency:
One baby out of every 18,000 is born with a genetic defect of not being able to utilize galactose. Since galactose is in milk as part of lactose, it will build up in the blood and urine. Undiagnosed it may lead to mental retardation, failure to grow, formation of cataracts, and in sever cases death by liver damage. The disorder is caused by a deficiency in one or more enzymes required to metabolize galactose.
The treatment for the disorder is to use a formula based upon the sugar sucrose rather than milk with lactose. The galactose free diet is critical only in infancy, since with maturation another enzyme is developed that can metabolize galactose.
Click for larger image
Ring Structure for Galactose:
The chair form of galactose follows the same pattern as that for glucose.
Open graphic of glucose in a new window
Hemiacetal Functional Group:
The anomeric carbon is the center of a hemiacetal functional group. A carbon that has both an ether oxygen and an alcohol group is a hemiacetal.
Open graphic of hemiacetal in a new window
Which carbon in the structure on the left is the anomeric carbon?
Then check the answer from the drop down menu.
Compare Alpha and Beta Galactose in the Chair form (left graphic):
The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal projection,(Haworth - an upwards projection).
The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the chair and Haworth structure this results in a downward projection.
Click for larger image
Compare Glucose and Galactose in the Chair Structures:
The position of the -OH group on the carbon (#4) is the only distinction between glucose and galactose.
Glucose is defined as the -OH on C # 4 in a horizontal projection in the chair form, (down in the Haworth structure).
Galactose is defined as the -OH on C # 4 in a upward projection in the chair form,(also upward in the Haworth structure).
Both glucose and galactose may be either alpha or beta on the anomeric carbon, so this is not distinctive between them
Carbon # 1
Fructose
Fructose is more commonly found together with glucose and sucrose in honey and fruit juices. Fructose, along with glucose are the monosaccharides found in disaccharide, sucrose.
Fructose is classified as a monosaccharide, the most important ketose sugar, a hexose, and is a reducing sugar.
An older common name for fructose is levulose, after its levorotatory property of rotating plane polarized light to the left (in contrast to glucose which is dextrorotatory).
Bees gather nectar from flowers which contains sucrose. They then use an enzyme to hydrolyze or break apart the sucrose into its component parts of glucose and fructose.
High Fructose Corn Syrup
Click for larger image
Ring Structure for Fructose:
The chair form of fructose follows a similar pattern as that for glucose with a few exceptions. Since fructose has a ketone functional group, the ring closure occurs at carbon # 2. See the graphic on the left.
In the case of fructose a five membered ring is formed. The -OH on carbon #5 is converted into the ether linkage to close the ring with carbon #2. This makes a 5 member ring - four carbons and one oxygen.
Steps in the ring closure (hemiketal synthesis):1. The electrons on the alcohol oxygen are used to bond the carbon #2 to make an ether (red oxygen atom).2. The hydrogen (green) is transferred to the carbonyl oxygen (green) to make a new alcohol group (green).
The ring structure is written with the orientation depicted on the left for the monosaccharide and is consistent with
the way the glucose is depicted.
Hemiketal Functional Group:
The anomeric carbon is the center of a hemiketal functional group. A carbon that has both an ether oxygen and an alcohol group (and is attached to two other carbons is a hemiketal.
Open graphic of hemiacetal/hemiketal in a new window
Which carbon in the structure on the left is the anomeric carbon?Then check the answer from the drop down menu.
Compare Alpha and Beta Fructose:
The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the ring structure this results in a upwards projection for the -OH on carbon # 2.
The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the ring structure this results in a downward projection for the -OH on carbon # 2.
The alpha and beta label is not applied to any other carbon - only the anomeric carbon, in this case # 2.
Open graphic of Alpha/Beta Fructose in a new window
Compare Alpha and Beta Fructose - Chime in new window
Carbon # 2
Click for larger image
Compare Glucose and Fructose in the Chair Structures:
The six member ring and the position of the -OH group on the carbon (#4) identifies glucose from the -OH on C # 4 in a down projection in the Haworth structure).
Fructose is recognized by having a five member ring and having six carbons, a hexose.
Both glucose and fructose may be either alpha or beta on the anomeric carbon, so this is not distinctive between them
Maltose
Maltose is made from two glucose units:
Maltose or malt sugar is the least common disaccharide in nature. It is present in germinating grain, in a small proportion in corn syrup, and forms on the partial hydrolysis of starch. It is a reducing sugar.
The two glucose units are joined by an acetal oxygen bridge in the alpha orientation. To recognize glucose look for the down or horizontal projection of the -OH on carbon # 4. See details on the galactose page towards the bottom.
Malted Barley:
Beer is made from four basic building blocks: water, malted barley, and hops.
Barley, a basic cereal grain, is low in gluten, and is not particularly good for milling into flour for use in products such as bread. Barley is the preferred grain to make beer. The barley grains must be "malted" before they can be used in the
brewing process.
Malting is a process of bringing grain to the point of its highest possible starch content by allowing it to begin to sprout roots and take the first step to becoming a photosynthesizing plant.
At the point when the maximum starch content is reached, the seed growth is stopped by heating the grain to a temperature that stops growth but allows an important natural enzyme diastase to remain active. Barley, once "malted" is very high in the type of starches that an enzyme called diastase (found naturally on the surface of the grain, just under the husk) can convert starch quite easily into the disaccharide called Maltose. This sugar is then fermented or metabolized by the yeasts to create carbon dioxide and ethyl alcohol.
Adapted from: Beer Basics
Acetal Functional Group:
Carbon # 1 (red on left) is called the anomeric carbon and is the center of an acetal functional group. A carbon that has two ether oxygens attached is an acetal.
The Alpha position is defined as the ether oxygen being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection. This is the same definition as the -OH in a hemiacetal.
Open graphic of hemiacetal in a new window
Maltose - Chime in new window
Hydrolysis of Starch:
In the hydrolysis of any di- or poly saccharide, a water molecule helps to break the acetal bond as shown in red. The acetal bond is broken, the H from the water is added to the oxygen on one glucose.
The -OH is then added to the carbon on the other glucose. In this case the diastase enzyme is very specific and cuts the starch chain in units of two glucose which happens to be maltose.
Lactose
Lactose is made from galactose and glucose units:
Lactose or milk sugar occurs in the milk of mammals - 4-6% in cow's milk and 5-8% in human milk. It is also a by product in the the manufacture of cheese.
The galactose and glucose units are joined by an acetal oxygen bridge in thebeta orientation. To recognize galactose look for the upward projection of the -OH on carbon # 4. See details on the galactose page towards the bottom.
Lactose intolerance:
Lactose intolerance is the inability to digest significant amounts of lactose, the predominant sugar of milk. This inability results from a shortage of the enzyme lactase, which is normally produced by the cells that line the small intestine. Lactase breaks down the lactose, milk sugar, into glucose and galactose that can then be absorbed into the bloodstream. When there is not
enough lactase to digest the amount of lactose consumed, produce some uncomfortable symptoms. Some adults have low levels of lactase. This leads to lactose intolerance. The ingested lactose is not absorbed in the small intestine, but instead is fermented by bacteria in the large intestine, producing uncomfortable volumes of carbon dioxide gas. While not all persons deficient in lactase have symptoms, those who do are considered to be lactose intolerant.
Common symptoms include nausea, cramps, bloating, gas, and diarrhea, which begin about 30 minutes to 2 hours after eating or drinking foods containing lactose. The severity of symptoms varies depending on the amount of lactose each individual can tolerate.
Fortunately, lactose intolerance is relatively easy to treat by controlling the diet. No cure or treatment exists to improve the body's ability to produce lactase. Young children with lactase deficiency should not eat any foods containing lactose. Most older children and adults need not avoid lactose completely, but individuals differ in the amounts and types of foods they can handle. Dietary control of lactose intolerance depends on each person's learning through trial and error how much lactose he or she can handle.
Adapted from: Lactose Intolerance
Open graphic of hydrolysis of lactose in a new window
Acetal Functional Group:
Carbon # 1 (red on left) is called the anomeric carbon and is the center of an acetal functional group. A carbon that has two ether oxygens attached is an acetal.
The Beta position is defined as the ether oxygen being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal or up projection. This is the same definition as the -OH in a hemiacetal.
Open graphic of hemiacetal in a new window
Lactose - Chime in new window
Compare Lactose and Maltose Acetals:
The position of the oxygen in the acetal on the anomeric carbon (#1) is an important distinction for disaccharide chemistry.
Lactose has a beta acetal. The Beta position is defined as the oxygen in the acetal being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal projection.
Maltose has an alpha acetal. The Alpha position is defined as the oxygen in the acetal being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection.
The alpha and beta acetal label is not applied to any other carbon - only the anomeric carbon of the left monosaccharide, in this case # 1 (red).
Recognize galactose and glucose:
To further identify lactose and maltose, identify the presence of galactose in lactose in the left most structure by the upward -OH on the carbon # 4.
Identify glucose in maltose in the left most structure by the horizontal -OH on the carbon # 4.
Sucrose is made from glucose and fructose units:
Sucrose or table sugar is obtained from sugar cane or sugar beets.
The glucose and fructose units are joined by an acetal oxygen bridge in thealpha orientation. The structure is easy to recognize because it contains the six member ring of glucose and the five member ring of fructose.
To recognize glucose look for the horizontal projection of the -OH on carbon # 4. See details on the galactose page towards the bottom.
The alpha acetal is is really part of a double acetal, since the two monosaccharides are joined at the hemiacetal of glucose and the hemiketal of the fructose. There are no hemiacetals remaining in the sucrose and therefore sucrose is a non-reducing sugar.
Sugar and Tooth Decay
Sugar Processing:
Sugar or more specifically sucrose is a carbohydrate that occurs naturally in every fruit and vegetable. It is the major product of photosynthesis, the process by which plants transform the sun's energy into food. Sugar occurs in greatest quantities in sugar cane and sugar beets from which it is separated for commercial use.
In the first stage of processing the
natural sugar stored in the cane stalk or beet root is separated from the rest of the plant material by physical methods. For sugar cane, this is accomplished by: a) pressing the cane to extract the juice containing the sugar b) boiling the juice until it begins to thicken and sugar begins to crystallize c) spinning the sugar crystals in a centrifuge to remove the syrup, producing raw sugar; the raw sugar still contains many impuritiesd) shipping the raw sugar to a refinery where it is washed and filtered to remove remaining non-sugar ingredients and color e) crystallizing, drying and packaging the refined sugar.
Beet sugar processing is similar, but it is done in one continuous process without the raw sugar stage. The sugar beets are washed, sliced and soaked in hot water to separate the sugar-containing juice from the beet fiber. The sugar-laden juice is purified, filtered, concentrated and dried in a series of steps similar to cane sugar processing.
Adapted from: Sugar Facts
Acetal Functional Group:
Carbon # 1 (red on left) is called the anomeric carbon and is the center of an acetal functional group. A carbon that has two ether oxygens attached is an acetal.
The Alpha position is defined as the ether oxygen being on the opposite side of the ring as the C # 6. In the chair structure this results in a down projection. This is the same definition as the -OH in a hemiacetal.
A second acetal grouping is defined by the green atoms. This result because the the formation reaction of the disaccharide is between the hemiacetal of glucose and the hemiketal of the fructose.
Open graphic of hemiacetal in a new window
Sucrose - Chime in new window
Invert Sugar:
When sucrose is hydrolyzed it forms a 1:1 mixture of glucose and fructose. This mixture is the main ingredient in honey. It is called invert sugar because the angle of the specific rotation of the plain polarized light changes from a positive to a negative value due to the presence of the optical isomers of the mixture of glucose and fructose sugars.
Hydrolysis of Sucrose:
In the hydrolysis of any di- or poly saccharide, a water molecule helps to break the acetal bond as shown in red. The acetal bond is broken, the H from the water is added to the oxygen on the glucose.
The -OH is then added to the carbon on the fructose.
Click for larger image
StarchPolysaccharides are carbohydrate polymers consisting of tens to hundreds to several thousand monosaccharide units. All of the common polysaccharides contain glucose as the monosaccharide unit. Polysaccharides are synthesized by plants, animals, and humans to be stored for food, structural support, or metabolized for energy.
Starch can be separated into two fractions--amylose and amylopectin. Natural starches are mixtures of amylose (10-20%) and amylopectin (80-90%).
Amylose forms a colloidal dispersion
in hot water whereas amylopectin is completely insoluble. The structure of amylose consists of long polymer chains of glucose units connected by an alpha acetal linkage. The graphic on the left shows a very small portion of an amylose chain. All of the monomer units are alpha -D-glucose, and all the alpha acetal links connect C # 1 of one glucose to C # 4 of the next glucose.
Starch - Amylose - Chime in new window
Acetal Functional Group:
Carbon # 1 is called the anomeric carbon and is the center of an acetal functional group. A carbon that has two ether oxygens attached is an acetal.
The Alpha position is defined as the ether oxygen being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection. This is the same definition as the -OH in a hemiacetal.
Open graphic of hemiacetal in a new window
Click for larger image
Starch Coil or Spiral Structure:
As a result of the bond angles in the alpha acetal linkage, amylose actually forms a spiral much like a coiled spring.
Amylose is responsible for the formation of a deep bluecolor in the presence of iodine. The iodine molecule slips inside of the amylose coil.
Starch Coil - Chime in new window
Click for larger image
Amylopectin:
The graphic on the left shows very small portion of an amylopectin-type structure showing two branch points [drawn closer together than they should be]. The acetal linkages are alpha connecting C # 1 of one glucose to C # 4 of the next glucose.
The branches are formed by linking C # 1 to a C # 6 through an acetal linkages. Amylopectin has 12-20 glucose units between the branches. Natural starches are mixtures of amylose and amylopectin.
In glycogen, the branches occur at intervals of 8-10 glucose units, while in amylopectin the branches are separated by 10-12 glucose units.
CellulosePolysaccharides are carbohydrate polymers consisting of tens to hundreds to several thousand monosaccharide units. All of the common polysaccharides contain glucose as the monosaccharide unit. Polysaccharides are synthesized by plants, animals, and humans to be stored for food, structural support, or metabolized for energy.
Cellulose:
The major component in the rigid cell walls in plants is cellulose. Cellulose is a linear polysaccharide polymer with many glucose monosaccharide units. The acetal linkage is beta which makes it different from starch. This peculiar difference in acetal linkages results in a major difference in digestibility in humans. Humans are unable to digest cellulose because the appropriate enzymes to breakdown the beta acetal linkages are lacking. (More on enzyme digestion in a later chapter.) Undigestible cellulose is the fiber which aids in the smooth working of the intestinal tract.
Animals such as cows, horses, sheep, goats, and termites have symbiotic bacteria in the intestinal tract. These symbiotic bacteria possess the necessary enzymes to digest cellulose in the GI tract. They have the required enzymes for the breakdown or hydrolysis of the cellulose; the animals do not, not even termites, have the correct enzymes. No vertebrate can digest cellulose directly.
Even though we cannot digest cellulose, we find many uses for it including: Wood for building; paper products; cotton, linen, and rayon for clothes; nitrocellulose for explosives; cellulose acetate for films.
The structure of cellulose consists of long polymer chains of glucose units connected by a beta acetal linkage. The graphic on the left shows a very small portion of a cellulose chain. All of the monomer units are beta-D-glucose, and all the beta acetal links connect C # 1 of one glucose to C # 4 of the next glucose.
Cellulose - Chime in new window
Acetal Functional Group:
Carbon # 1 is called the anomeric carbon and is the center of an acetal functional group. A carbon that has two ether oxygens attached is an acetal.
The Beta position is defined as the ether oxygen being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal or up projection. This is the same definition as the -OH in a hemiacetal.
Open graphic of hemiacetal in a new window
Compare Cellulose and Starch Structures:
Cellulose: Beta glucose is the monomer unit in cellulose. As a result of the bond angles in the beta acetal linkage, cellulose is mostly a linear chain.
Starch: Alpha glucose is the monomer unit in starch. As a result of the bond angles in the alpha acetal linkage, starch-amylose actually forms a spiral much like a coiled spring.
Compare Starch and Cellulose - Chime in new window
Fiber in the Diet:
Dietary fiber is the component in food not broken down by digestive enzymes and secretions of the gastrointestinal tract. This fiber includes hemicelluloses, pectins, gums, mucilages, cellulose, (all carbohydrates) and lignin, the only non-carbohydrate component of dietary fiber.
High fiber diets cause increased stool size and may help prevent or cure constipation. Cereal fiber, especially bran, is most effective at increasing stool size while pectin has little effect. Lignin can be constipating.
Fiber may protect against the development of colon cancer, for populations consuming high fiber diets have a low incidence of this disease. The slow transit time (between eating and elimination) associated with a low fiber intake would allow more time for carcinogens present in the colon to initiate cancer. But constipated people do not have a higher incidence of colon cancer than fast eliminators, so fiber's role in colon cancer remains unclear.
Dietary fiber may limit cholesterol absorption by binding bile acids. High fiber diets lower serum cholesterol and may prevent cardiovascular disease. Some fibers, such as pectin and rolled oats, are more effective than others, such as wheat, at lowering serum cholesterol.
Dietary fiber is found only in plant foods such as fruits, vegetables, nuts, and grains. Whole wheat bread contains more fiber than white bread and apples contain more fiber than apple juice, which shows that processing food generally removes fiber.
Click for larger image
GlycogenPolysaccharides are carbohydrate polymers consisting of tens to hundreds to several thousand monosaccharide units. All of the common polysaccharides contain glucose as the monosaccharide unit. Polysaccharides are synthesized by plants, animals, and humans to be stored for food, structural support, or metabolized for energy.
Glycogen:
Glycogen is the storage form of glucose in animals and humans which is analogous to the starch in plants. Glycogen is synthesized and stored mainly in the liver and the muscles. Structurally, glycogen is very similar to amylopectin with alpha acetal linkages, however, it has even more branching and more glucose units are present than in amylopectin. Various samples of glycogen have been measured at 1,700-600,000 units of glucose.
The structure of glycogen consists of long polymer chains of glucose units connected by an alpha acetal linkage. The graphic on the left shows a very small portion of a glycogen chain. All of the monomer units are alpha-D-glucose, and all the alpha acetal links connect C # 1 of one glucose to C # 4 of the next glucose.
The branches are formed by linking C # 1 to a C # 6 through an acetal linkages. In glycogen, the branches occur at intervals of 8-10 glucose units, while in amylopectin the branches are separated by 12-20 glucose units.
Glycogen - Chime in new window
Acetal Functional Group:
Carbon # 1 is called the anomeric carbon and is the center of an acetal functional group. A carbon that has
two ether oxygens attached is an acetal.
The Alpha position is defined as the ether oxygen being on the opposite side of the ring as the C # 6. In the chair structure this results in a downward projection. This is the same definition as the -OH in a hemiacetal.
Open graphic of hemiacetal in a new window
Starch vs. Glycogen:
Plants make starch and cellulose through the photosynthesis processes. Animals and human in turn eat plant materials and products. Digestion is a process of hydrolysis where the starch is broken ultimately into the various monosaccharides. A major product is of course glucose which can be used immediately for metabolism to make energy. The glucose that is not used immediately is converted in the liver and muscles into glycogen for storage by the process of glycogenesis. Any glucose in excess of the needs for energy and storage as glycogen is converted to fat.
Ribose
Ribose and its related compound, deoxyribose, are the building blocks of the backbone chains in nucleic acids, better known as DNA and RNA. Ribose is used in RNA and deoxyribose is used in DNA. The deoxy- designation refers to the lack of an alcohol, -OH, group as will be shown in detail further down.
Ribose and deoxyribose are classified as monosaccharides, aldoses, pentoses, and are reducing sugars.
Click for larger image
Ring Structure for Ribose:
The chair form of ribose follows a similar pattern as that for glucose with one exception. Since ribose has an aldehyde functional group, the ring closure occurs at carbon # 1, which is the same as glucose. See the graphic on the left.
The exception is that ribose is a pentose, five carbons. Therefore a five membered ring is formed. The -OH on carbon #4 is converted into the ether linkage to close the ring with carbon #1. This makes a 5 member ring - four carbons and one oxygen.
Steps in the ring closure (hemiacetal synthesis):1. The electrons on the alcohol oxygen are used to bond the carbon #1 to make an ether (red oxygen atom).2. The hydrogen (green) is transferred to the carbonyl oxygen (green) to make a new alcohol group (green).
The chair structures are always written with the orientation depicted on the left to avoid confusion.
Hemiacetal Functional Group:
Carbon # 1 is now called the anomeric carbon and is the center of a hemiacetal functional group. A carbon that has both an ether oxygen and an alcohol group is a hemiacetal.
Open graphic of hemiacetal in a new window
Click for larger image
Compare Ribose and Deoxyribose Structures:
The presence or absence of the -OH group on carbon (#2) is an important distinction between ribose and deoxyribose. Ribose has an alcohol at carbon # 2, while deoxyribose does not have the alcohol group. See red -OH and H in the structures on the left.
The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the ring structure this results in a upward projection.
The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the ring structure this results in a downward projection.
The alpha and beta label is not applied to any other carbon - only the anomeric carbon, in this case # 1.
Dextrose
Dextrose, commonly called glucose, d-glucose, or blood sugar, occurs naturally in food, and is moderately sweet. It is a monosaccharide (basic unit of carbohydrates, C6H1206) and has a high glycemic index (digested carbohydrates ability to raise blood glucose levels, also called Gl) ranking at 100.
Amylopectin is a polysaccharide with a varying structure; It is composed of linearly linked alpha 1,4 linked glucose units (coiled into tubular sections) with occasional alpha 1-6 glycosidic bonds which provide branching points. Each amylopectin molecule may contain 100,000-200,000 glucose units, and each branch is about 20 or 30 glucose units in length, so that these molecules are bushy and nearly spherical in shape.
The many exposed ends can have more glucose units added to them by enzyme action for storage
purposes or removed from them for use in respiration.
Amylopectin is one fraction of starch (typicaly 80-90%), the other fraction being amylose (10-20%). Glycogen ("animal starch"), found in the liver and muscles, is effectively similar in structure to amylopectin, but it has shorter branches: 8-12 glucose units.
This simple model - specifically prepared for this website by the Sweet program - shows 84 glucose units. The 1-4 linked sections can be seen to coil into a helical shape, and the 1-6 linkage forms a helical branch away from the main section.
Starch
Starch is the major form of stored carbohydrate in plants. Starch is composed of a mixture of two substances: amylose, an essentially linear polysaccharide, and amylopectin, a highly branched
polysaccharide. Both forms of starch are polymers of α-D-Glucose. Natural starches contain 10-20% amylose and 80-90% amylopectin. Amylose forms a colloidal dispersion in hot water (which helps to thicken gravies) whereas amylopectin is completely insoluble.
Amylose molecules consist typically of 200 to 20,000 glucose units which form a helix as a result of the bond angles between the glucose units.
Amylose
Amylopectin differs from amylose in being highly branched. Short side chains of about 30 glucose units are attached with 1α→6 linkages approximately every twenty to thirty glucose units along the chain. Amylopectin molecules may contain up to two million glucose units.
Amylopectin
The side branching chains are clustered together within the amylopectin molecule
Starches are transformed into many commercial products by hydrolysis using acids or enzymes as catalysts. Hydrolysis is a chemical reaction in which water is used to break long polysaccharide chains into smaller chains or into simple carbohydrates. The resulting products are assigned a Dextrose
Equivalent (DE) value which is related to the degree of hydrolysis. A DE value of 100 corresponds to completely hydrolyzed starch, which is pure glucose (dextrose). Dextrinsare a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch. Dextrins are mixtures of polymers of D-glucose units linked by 1α→4 or 1α→6 glycosidic bonds. Maltodextrin is partially hydrolyzed starch that is not sweet and has a DE value less than 20. Syrups, such as corn syrup made from corn starch, have DE values from 20 to 91. Commercial dextrose has DE values from 92 to 99. Corn syrup solids, which may be labeled as soluble corn fiber or resistant maltodextrin, are mildly sweet semi-crystalline or powdery amorphous products with DEs from 20 to 36 made by drying corn syrup in a vacuum or in spray driers. Resistant maltodextrin or soluble corn fiber are not broken down in the digestive system, but they are partially fermented by colonic bacteria thus providing only 2 Calories per gram instead of the 4 Calories per gram in corn syrup. High Fructose Corn Syrup (HFCS), commonly used to sweeten soft drinks, is made by treating corn syrup with enzymes to convert a portion of the glucose into fructose. Commercial HFCS contains from 42% to 55% fructose, with the remaining percentage being mainly glucose. There is an effort underway to rename High Fructose Corn Syrup as Corn Sugar because of the negative public perception that HFCS contributes to obesity. Modified starch is starch that has been changed by mechanical processes or chemical treatments to stabilize starch gels made with hot water. Without modification, gelled starch-water mixtures lose viscosity or become rubbery after a few hours. Hydrogenated glucose syrup (HGS) is produced by hydrolyzing starch, and then hydrogenating the resulting syrup to produce sugar alcohols like maltitol and sorbitol, along with hydrogenated oligo- and polysaccharides. Polydextrose (poly-D-glucose) is a synthetic, highly-branched polymer with many types of glycosidic linkages created by heating dextrose with an acid catalyst and purifying the resulting water-soluble polymer. Polydextrose is used as a bulking agent because it is tasteless and is similar to fiber in terms of its resistance to digestion. The name resistant starch is applied to dietary starch that is not degraded in the stomach and small intestine, but is fermented by microflora in the large intestine.
Relative sweetness of various carbohydrates
fructose 173invert sugar* 120HFCS (42% fructose) 120sucrose 100xylitol 100tagatose 92glucose 74high-DE corn syrup 70sorbitol 55
mannitol 50trehalose 45regular corn syrup 40galactose 32maltose 32lactose 15
Amylose is a linear polymer made up of D-glucose units.
This polysaccharide is one of the two components
of starch, making up approximately 20-30% of the
structure. The other component is amylopectin,
which makes up 70-80% of the structure.[1]
Because of its tightly packed structure, amylose is
more resistant to digestion than other starch
molecules and is therefore an important form
of resistant starch, which has been found to be an
effective prebiotic.[2]
[edit]Structure
Amylose is made up of α(1→4) bound glucose
molecules. The carbon atoms on glucose are
numbered, starting at the aldehyde (C=O) carbon,
so, in amylose, the 1-carbon on one glucose
molecule is linked to the 4-carbon on the next
glucose molecule (α(1→4) bonds).[3] The structural
formula of amylose is pictured at right. The number
of repeated glucose subunits (n) is usually in the
range of 300 to 3000, but can be many thousands.
There are three main forms of amylose chains can
take. It can exist in a disordered amorphous
conformation or two different helical forms. It can
bind with itself in a double helix(A or B form), or it
can bind with another hydrophobic guest molecule
such as iodine, a fatty acid, or an aromatic
compound. This is known as the V form and is
how amylopectin binds to amylose to form starch.
Within this group, there are many different
variations. Each is notated with V and then a
subscript indicating the number of glucose units per
turn. The most common is the V6 form, which has six
glucose units a turn. V8 and possibly V7 forms exist
as well. These provide an even larger space for the
guest molecule to bind.[4]
This linear structure can have some rotation around
the phi and psi angles, but, for the most part, bound
glucose ring oxygens lie on one side of the structure.
The α(1→4) structure promotes the formation of
a helix structure, making it possible for hydrogen
bonds form between the oxygen atoms bound at 2-
carbon of one glucose molecule and the 3-carbon of
the next glucose molecule.[5]
[edit]Physical properties
Unlike amylopectin, amylose is insoluble in water.[6] It also reduces the crystallinity of amylopectin and
how easily water can infiltrate the starch.[7] The
higher the amylose content, the less expansion
potential and the lower the gel strength for the same
starch concentration. This can be countered partially
by increasing the granule size.[8]
Fiber X-ray diffraction analysis coupled with
computer-based structure refinement has found A-,
B-, and C- polymorphs of amylose. Each form
corresponds to either the A-, the B-, or the C- starch
forms. A- and B- structures have different helical
crystal structures and water contents, whereas the
C- structure is a mixture of A- and B- unit cells,
resulting in an intermediate packing density
between the two forms.[9]
[edit]Function
Amylose is important in plant energy storage. It is
less readily digested than amylopectin; however,
because it is more linear than amylopectin, it takes
up less space. As a result, it is the preferred starch
for storage in plants. It makes up about 30% of the
stored starch in plants, though the specific
percentage varies by species. The digestive enzyme
α-amylase is responsible for the breakdown of the
starch molecule into maltotriose and maltose, which
can be used as sources of energy.
Amylose is also an important thickener, water
binder, emulsion stabilizer, and gelling agent in both
industrial and food-based contexts. Loose helical
amylose chains have a hydrophobic interior that can
bind to hydrophobic molecules such
as lipids and aromatic compounds. The one problem
with this is that, when it crystallizes or associates, it
can lose some stability, often releasing water in the
process (syneresis). When amylose concentration is
increased, gel stickiness decreases but gel firmness
increases. When other things
including amylopectin bind to amylose,
the viscosity can be affected, but incorporating κ-
carrageenan, alginate, xanthan gum, or low-
molecular-weight sugars can reduce the loss in
stability. The ability to bind water can add substance
to food, possibly serving as a fat replacement.[10] For
example, amylose is responsible for causing white
sauce to thicken, but, upon cooling, some separation
between the solid and the water will occur.
In a laboratory setting, it can act as a
marker. Iodine molecules fit neatly inside the helical
structure of amylose, binding with the starch
polymer that absorbs certain known wavelengths of
light. Hence, a common test is the iodine test for
starch. Mix starch with a small amount of yellow
iodine solution. In the presence of amylose, a blue-
black color will be observed. The intensity of the
color can be tested with a colorimeter, using a red
filter to discern the concentration of starch present
in the solution. It is also possible to use starch as an
indicator in titrations involving iodine reduction.[11] It
is also used in amylose magnetic beads and resin to
separate maltose-binding protein [12]
[edit]Recent studies
High-amylose varieties of rice, the less sticky long-
grain rice, have a much lower glycemic load, which
could be beneficial for diabetics.
Researchers have identified the gene granular
binding starch synthase, or GBSS, in potatoes. It is
responsible for encoding for the enzyme that directs
amylase starch production. If it is inhibited, amylose
production will also be interrupted.[13
What is Amylose?Amylose is a group of carbohydrate chains that includes dextrin and cellulose. The term carbohydrate simply means carbon, hydrogen and oxygen and refers to whole grains, legumes, fruits and vegetables. Dextrin aids in the breakdown of starch during digestion. Cellulose is the fibrous form of the molecule that aids in the transport of starch during digestion. The amylose molecule provides a high fiber source with a low glycemic index. The more amylose present, the lower the glycemic index. Diabetics may benefit from a diet high in amylose because of the slower insulin response, which prevents quick spikes in glucose levels. Research is being conducted on the benefits of a high amylose diet
in the prevention of colon cancer and heart disease.Whole GrainsWhole-grain foods have a significant amount of amylose and include wheat, wild rice, rye, barley, oats, bulgur, corn, millet, quinoa, amaranth, barley, buckwheat, sorghum and triticale, a hybrid between wheat and rye. The U.S. Food and Drug Administration recommends that food products labeled "whole grain" should include an intact grain that has not had the endosperm, germ or bran removed. Breads, cereals and certain pastas labeled "whole grain" may have a higher amylose content than foods simply labeled "wheat," such as in wheat bread. Regular white rice and pastas are not high in amylose and do not have a low glycemic index.LegumesLegumes refer to dried beans, lentils and peas and are an abundant source of amylose. Black-eyed peas, lentils, black, garbanzo, chili, great northern and kidney beans are some of the many dried beans and peas available. Dried legumes can be soaked and boiled for use on salads or in soups. Some beans can be mashed and used as spreads and dips such as hummus.Other Foods
Bananas have a high amylose content. Certain root vegetables are also high in amylose, such as sweet potatoes, radishes and parsnips. White potatoes do not have many of the complex chains of the amylose molecule and are not considered a low glycemic index food. Amylose or resistant starch in powder form is available to help boost fiber in smoothies and baked goods.
Galactomannan
Galactomannans are polysaccharides consisting of a mannose backbone with galactose side groups. The mannopyranose units are linked with 1β→4 linkages to which galactopyranose units are attached with 1α→6 linkages. Galactomannans are present in several vegetable gums that are used to increase the viscosity of food products. These are the approximate ratios of mannose to galactose for the following gums:
Fenugreek gum, mannose:galactose 1:1 Guar gum, mannose:galactose 2:1 Tara gum, mannose:galactose 3:1 Locust bean gum or Carob gum,
mannose:galactose 4:1
Guar is a legume that has been traditionally cultivated as livestock feed. Guar gum is also known by the namecyamopsis tetragonoloba which is the Latin taxonomy for the guar bean or cluster bean. Guar gum is the ground endosperm of the seeds. Approximately 85% of guar gum is guaran, a water soluble polysaccharide consisting of linear chains of mannose with 1β→4 linkages to which galactose units are attached with 1α→6 linkages. The ratio of mannose to galactose is 2:1. Guar gum has five to eight times the thickening power of starch and has many uses in the pharmaceutical industry, as a food stabilizer, and as a source of dietary fiber.
Guaran is the principal polysaccharide in guar gum.
Arabinoxylan
Arabinoxylans are polysaccharides found in the bran of grasses and grains such as wheat, rye, and barley. Arabinoxylans consist of a xylan backbone with L-arabinofuranose (L-arabinose in its 5-atom ring form) attached randomly by 1α→2 and/or 1α→3
linkages to the xylose units throughout the chain. Since xylose and arabinose are both pentoses, arabinoxylans are usually classified as pentosans. Arabinoxylans are important in the baking industry. The arabinose units bind water and produce viscous compounds that affect the consistency of dough, the retention of gas bubbles from fermentation in gluten-starch films, and the final texture of baked products.
Arabinoxylan
Chitin
Chitin is an unbranched polymer of N-Acetyl-D-glucosamine. It is found in fungi and is the principal component of arthropod and lower animal exoskeletons, e.g., insect, crab, and shrimp shells. It may be regarded as a derivative of cellulose, in which the hydroxyl groups of the second carbon of each glucose unit have been replaced with acetamido (-NH(C=O)CH3) groups.
Chitin
Fucoidan is a sulfated polysaccharide (MW:
average 20,000) found mainly in various species
of brown algae and brown seaweed such
as mozuku, kombu, limu moui, bladderwrack, wakam
e, and hijiki (variant forms of fucoidan have also been
found in animal species, including the sea cucumber).
Fucoidan is used as an ingredient in some dietary
supplement products.
[edit]Research
There at least two distinct forms of fucoidan: F-
fucoidan, which is >95% composed of
sulfated esters of fucose, and U-fucoidan, which is
approximately 20% glucuronic acid.
The physiological and biochemical effects of fucoidan
have been examined in several small-scale in
vitro and animal studies. F-fucoidan was reported to
inhibit hyperplasia in rabbits [1] and
induce apoptosis in isolated human lymphoma cell
lines in vitro.[2]. It has been hypothesized that these
two effects may involve a common mechanism, but
the evidence is inconsistent and no mechanism for
the putative induction of apoptosis by fucoidan has
been identified.[3] A study in rats indicated that pre-
treatment with fucoidan increases mortality
subsequent to meningitis infection.[4] In a clinical
study, orally-ingested Undaria-derived-fucoidan was
reported to produce a small increase in the total
number of CD34+ cells, and a more pronounced
increase in the proportion of CD34+ cells that
expressedCXCR4. The authors of the study
hypothesized that the ability of fucoidan to mobilize
hematopoetic cells with high levels of CXCR4
expression could be clinically valuable.[5]
Mannan is a plant polysaccharide that is
a polymer of the sugar mannose.[1]
Detection of mannan leads to lysis in the mannan-
binding lectin pathway.It is generally found in yeast,
bacteria and plants. Plant mannans have β(1-4)
linkages. It is a form of storage polysaccharide. Ivory
nut is composed of mannan.
Xylan (CAS number:9014-63-5) is a generic term used to describe a wide variety of highly
complex polysaccharides that are found in plant cell
walls and some algae. Xylans are polysaccharides
made from units of xylose (a pentose sugar).
Xylan is found in the cell walls of some green algae,
especially macrophytic siphonous genera , where it
replaces cellulose. Similarly, it replaces the inner
fibrillar cell-wall layer of cellulose in some red algae.
Xylan is one of the foremost anti-nutritional factors in
common use feedstuff raw materials. Laminarin is a polysaccharide carbohydrate very much like starch,
except it functions as an energy storage compound
for Laminaria and other brown algae like kelp. These
are large seaweeds of about thirty different genera. It
grows in underwater kelp forests in clear shallow salt
water and requires reasonably warm nutrient rich
water.
Laminarin is clearly a high-energy carbohydrate. It is directly produced
by photosynthesis in an algae that grows in long
stalks at the rate of as much as 30 centimeters per
day, up to 60 meters total. Laminarin is the nutrient-
rich part of kelp that feeds hundreds of sea animals.
In addition, kelp is an important part of the Japanese
diet and the diets of several other sea-dependent
cultures.
Though we don't yet know much about laminarin, it
has some very useful properties. It is rich in iodines
and alkali, as well as calcium. Ash produced by kelp is
used in soap and glass production, and laminarin can
be used as a thickener in several industries, like ice
cream, jelly, and toothpaste. Bladderwort is one form
of kelp that is used in several health-food products to
promote a healthy urinary tract, and it's probable
that the laminarin is part of what produces its
purported effects.
Chrysolaminarin is a linear polymer of β(1→3) and β(1→6) linked glucose units in a ratio of
11:1.[1][2] It used to be known as leucosin.
Chrysolaminarin is arguably one of the most common
biopolymers in the world with cellulose being the
other.
[edit]Function
Chrysolaminarin is a storage polysaccharide typically
found in photosynthetic heterokonts. It is used as a
carbohydrate food reserve by phytoplankton such
as Bacillariophyta (similar to the use
of laminarin by brown algae).[3]
Chrysolaminarin is stored inside the cells of these
organisms dissolved in water and encapsuled
in vacuoles whose refractive index increases with
chrysolaminarin content. In
addition, heterokont algae use oil as a storage
compound. Besides energy reserve, oil helps the
algae to control their buoyancy.[4]
Common Carbohydrates Name Derivation of name and Source
Monosaccharides
GlucoseFrom Greek word for sweet wine; grape sugar, blood sugar, dextrose.
GalactoseGreek word for milk--"galact", found as a component of lactose in milk.
Fructose
Latin word for fruit--"fructus", also known as levulose,found in fruits and honey; sweetest sugar.
RiboseRibose and Deoxyribose are found in the backbone structure of RNA and DNA, respectively.
Disaccharides - contain two monosaccharides
Sucrose
French word for sugar--"sucre", a disaccharide containingglucose and fructose; table sugar, cane sugar, beet sugar.
LactoseLatin word for milk--"lact"; a disaccharide found in milk containing glucose and galactose.
Maltose
French word for "malt"; a disaccharide containing two units of glucose; found in germinating grains, used to make beer.
Common Polysaccharides
Carbohydrate - MiniTopics
MiniTopics:
Glucose - Blood Sugar Chemical Test
Galactose - Galactosemia - Genetic Enzyme Deficiency
Maltose - Beer and Malted Barley
Lactose - Lactose Intolerance
Sucrose - Sugar and Tooth Decay
Starch - Corn Syrup and High Fructose Corn Syrup
Starch - Starch-Iodine Test
Sweetness - Sweeteners , Sweetness Scale, Sweet Receptor Site
Cellulose - Fiber in the Diet
Name Source
Starch
Plants store glucose as the polysaccharide starch. The cereal grains (wheat, rice, corn, oats, barley) as well as tubers such as potatoes are rich in starch.
Cellulose
The major component in the rigid cell walls in plants is cellulose and is a linear polysaccharide polymer with many glucose monosaccharide units.
Glycogen
This is the storage form of glucose in animals and humans which is analogous to the starch in plants. Glycogen is synthesized and stored mainly in the liver and the muscles.
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Carbohydrates - IntroductionIntroduction:
General names for carbohydrates include sugars, starches, saccharides, and polysaccharides. The term saccharide is derived from the Latin word " sacchararum" from the sweet taste of sugars.
The name "carbohydrate" means a "hydrate of carbon." The name derives from the general formula of carbohydrate is Cx(H2O)y - x and y may or may not be equal and range in value from 3 to 12 or more. For example glucose is: C6(H2O)6 or is more commonly written, C6H12O6.
The chemistry of carbohydrates most closely resembles that of alcohol, aldehyde, and ketone functional groups. As a result, the modern definition of a CARBOHYDRATE is that the compounds are polyhydroxy aldehydes or ketones. The chemistry of carbohydrates is complicated by the fact that there is a functional group (alcohol) on almost every carbon. In addition, the carbohydrate may exist in either a straight chain or a ring structure. Ring structures incorporate two additional functional groups: the hemiacetal and acetal.
A major part of the carbon cycle occurs as carbon dioxide is converted to carbohydrates through photosynthesis. Carbohydrates are utilized by animals and humans in metabolism to
produce energy and other compounds.
Click for larger imageCarbohydrate Functions:
Carbohydrates are initially synthesized in plants from a complex series of reactions involving photosynthesis.
-Store energy in the form of starch (photosynthesis in plants) or glycogen (in animals and humans).
-Provide energy through metabolism pathways and cycles.
-Supply carbon for synthesis of other compounds.
-Form structural components in cells and tissues.
Photosynthesis is a complex series of reactions carried out by algae, phytoplankton, and the leaves in plants, which utilize the energy from the sun. The simplified version of this chemical reaction is to utilize carbon dioxide molecules from the air and water molecules and the energy from the sun to produce a simple sugar such as glucose and oxygen molecules as a by product. The simple sugars are then converted into other molecules such as starch, fats, proteins, enzymes, and DNA/RNA i.e. all of the other molecules in living plants. All of the "matter/stuff" of a plant ultimately is produced as a result of this photosynthesis reaction.
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Metabolism:
Metabolism occurs in animals and humans after the ingestion of organic plant or animal foods. In the cells a series of complex reactions occurs with oxygen to convert for example glucose sugar into the products of carbon dioxide and water and ENERGY. This reaction is also carried out by bacteria in the decomposition/decay of waste materials on land and in the water. Combustion occurs when any organic material is reacted (burned) in the presence of oxygen to give off the products of carbon dioxide and water and ENERGY. The organic material can be any fossil fuel such as natural gas (methane), oil, or coal. Other organic materials that combust are wood, paper, plastics, and cloth. The whole purpose of both processes is to convert chemical energy into other forms of energy such as heat.
Di-, Poly-Carbohydrates - IntroductionIntroduction:
General names for carbohydrates include sugars, starches, saccharides, and polysaccharides. The term saccharide is derived from the Latin word " sacchararum" from the sweet taste of sugars.
Monosaccharides contain one sugar unit such as glucose, galactose, fructose, etc.
Disaccharides contain two sugar units. In almost all cases one of the sugars is glucose, with the other sugar being galactose, fructose, or another glucose. Common disaccharides are maltose, lactose, and sucrose.
Polysaccharides contain many sugar units in long polymer chains of many repeating units. The most common sugar unit is glucose. Common poly saccharides are starch, glycogen, and cellulos
Disaccharide descriptions and componentsDisaccharide Description Component monosaccharides
sucrose common table sugar glucose 1α→2 fructose
maltose product of starch hydrolysis glucose 1α→4 glucose
trehalose found in fungi glucose 1α→1 glucose
lactose main sugar in milk galactose 1β→4 glucose
melibiose found in legumes galactose 1α→6 glucose