•Dr. Hewida Fadel •Dr. Tarek El Sewedy Biochemistry 1 (MLBC-201)
Transcript
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Dr. Hewida Fadel Dr. Tarek El Sewedy
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By the end of this lecture, students will learn: 1.The basic
structure and classes of carbohydrates. 2.Biological function of
carbohydrates Intended Learning Outcomes
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Lecture content What are carbohydrates? Classification of
carbohydrates. Classification of monosaccharides. Reducing &
non reducing sugars. Classification of polysaccharides. Biological
function of carbohydrates
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Biomolecules of life 1. Carbohydrates 2. Proteins. 3. Lipids 4.
Nucleic acids
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What are carbohydrates? In biochemistry, carbohydrates is a
synonymous of saccharide. The word saccharide comes from the Greek
word skkharon, meaning sugar". The term carbohydrate often means
any food that is particularly rich in the comples carbohydrate
starch (such as cereals, bread, and pasta) or simple carbohydrates,
such as sugar (found in candy, jams, and
desserts).cerealsbreadpastacandyjamsdesserts Carbo-hydrate is
composed of carbon and water (C.H 2 O) n. For every carbon there is
1 water molecule or 2 hydrogen atoms and 1 oxygen atom (with some
exceptions).
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Classification of carbohydrates There are a variety of
classification schemes. The most common classification scheme
divides the carbohydrates into groups according to the number of
individual simple sugar units. Monosaccharides contain a single
unit disaccharides contain two sugar units (2 monosaccharides)
polysaccharides contain many sugar units as in polymers
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Monosaccharides can be further classified by the number of
carbons present. Six carbons = Hexose (ex. Glucose,
Galactose,fructose) Five carbons = Pentose (ex. Ribose) Four =
Tetrose (Erythose ) Three = Triose (Glyceraldehyde)
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Modified monosaccharides phosphorylated sugars are one example
of modified monosaccharides. An important phosphorylated sugar is
glucose 6-phosphate. glucose 6-phosphate provides energy in certain
metabolic pathways, and it can be converted and stored as glycogen
when blood glucose levels are high. If blood glucose levels are
low, glucose 6-phosphate can be converted back into glucose to
enter the bloodstream again. glucose 6-phosphate possesses a
negative charge. This prevents the molecule from leaving the
lipid-bilayer membranes. This allows the cell to easily uses the
modified sugar to provide energy, or convert it to glycogen as
storage.
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Classification according to Functional Groups Aldoses: Are
sugars containing an aldehyde functional group on carbon #1
(anomeric carbon)- Monosaccharides in this group are glucose,
galactose, ribose, and glyceraldehyde. Ketoses: Sugars containing
the ketone group on carbon # 2 (anomeric carbon)- The major sugar
in this group is fructose.
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Classification according to reducing capability Reducing
capability is defined by the presence of free aldehyde or ketone
group. A. Reducing: Contain free groups (contain one free anomeric
carbon atom), glucose, maltose, lactose and fructose. All
Monosaccharides are reducing sugars. Two of three disaccharides
maltose and lactose, have the free groups needed to act as reducing
agents. B. Non-reducing: Contain no free groups. Sucrose and
polysaccharides are non reducing. (sucrose's anomeric carbon is not
"free" since this carbon is used to link fructose and glucose
together.
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Reducing Disaccharides Lactose Maltose
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Non reducing disaccharide
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Classification of polysaccharides Homo-polysaccharides (all the
same type) Hetero-polysaccharides (mixtures of monomer types)
Complex carbohydrates (joined to non-carbohydrate molecules)
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Disaccharides fructoseglucosegalactose a sucrosemaltoselactose
(fructose-glucose)(glucose-glucose)(glucose- galactose)
monosaccharaides joined together to make disaccharides.
Carbohydrate Function Sources of Immediate energy (ATP) as
produced by glucose catabolism(Glycolysis and Krebs cycle). Source
of stored energy (Glycogen stored in liver). Intermediates in the
biosynthesis of other basic biomolecules (fats and proteins).
Associated with other molecules such as vitamins and
antibiotics.
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Cont, Carbohydrate function Structural function: ex. Ribose,
deoxyribose and cellulose and starch in plants. Involved in many
cell functions such cell-cell recognition and protein folding.
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Digestion of carbohydrates a) -amylase (in saliva) randomly
hydrolyzes all the glycosidic bonds of starch. By the time the
chewed food reaches the stomach, where acidity deactivates the
amylase, the average chain length of starch has gone from several
thousand to fewer than 8 glucose units. b) Digestion continues in
the small intestines with pancreatic amylase. This degrades the
starch to maltose. c) Further digestion occurs down the digestive
tract in the small intestine. The resulting monosaccharides are
absorbed by the small intestine and transported into the blood
stream
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In living organisms, most carbohydrates are found bound to
other compounds rather than as simple sugars Glycoproteins
(hormones, antibodies) Glycolipids Nucleic acid.
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Monosaccharaides Monosaccharaides are also known as simple
sugars They are classified by: 1. Number of carbons. 2. Whether
they are aldoses or ketoses. D-glyceraldehyde is the simplest of
the aldoses. Glucose is the most widely known
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Glucose Glucose is a monosaccharide with formula C 6 H 12 O 6
It is absorbed directly into the bloodstream during digestion.
Bread, rice, pasta are rich in glucose. Glucose is a common medical
analyte measured in blood samples. The insulin reaction, regulate
the concentration of glucose in the blood. A high fasting blood
sugar level is an indication of diabetic conditionsanalyte measured
in blood samplesblood sugar Glucose is used as an energy source in
most organisms aerobic or anaerobic respiration. The first step of
this is the phosphorylation of glucose by hexokinase to prepare it
for breakdown to provide energy. The major reason for the immediate
phosphorylation of glucose by a hexokinase is to prevent diffusion
out of the cell.phosphorylationhexokinase
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Organisms use glucose as a precursor for the synthesis of
several important substances. Starch, cellulose, and glycogen
("animal starch").Starchcelluloseglycogen Some of these polymers
like starch or glycogen serve as energy stores while others like
cellulose have structural roles. In plants, glucose is a product of
photosynthesis. In animals, glucose results from the breakdown of
glycogen, a process known as Glycogenolysis.glycogen In animals,
glucose is synthesized in the liver and kidneys from non-
carbohydrate intermediates, such as pyruvate and glycerol, by a
process known as Gluconeogenesis.liverkidneyspyruvateglycerol
Glucose is produced commercially via the enzymatic hydrolysis of
starch. Many crops can be used as the source of starch. Maize,
rice, wheatenzymatic hydrolysisMaizericewheat
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Glucose is classified as a monosaccharide, an aldose, a hexose,
and is a reducing sugar. Glucose is 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.
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Fructose
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Fructose is found naturally in fruits and vegetables. Fructose
is metabolized differently than glucose and other sugars, doesnt
stimulate insulin and is characteristically low glycemic. For these
reasons, its often used in low-glycemic food applications 15 to 80%
sweeter than sucrose, and tastes particularly sweet when cold or in
solution
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Disaccharides
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Disaccharides are formed when two monosaccharaides are joined
together and a molecule of water is removed. Milk sugar (lactose)
is made from glucose and galactoselactoseglucosegalactose sugar
cane sugar (sucrose) is made from glucose and
fructose.sucroseglucosefructose Maltose is made up of two glucose
molecules.Maltose The two monosaccharides are bonded via a
glycosidic bondmonosaccharidesglycosidic bond Can be degraded to
monosaccharides by hydrolysis producing water.
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Sucrose
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Formed of Glucose and fructose monomers joined together. known
as table sugar Commercially obtained from sugar cane or sugar beet
Used pharmaceutically to make syrups
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Lactose Lactose is a famous disaccharide, resulting from a
galactose joining to glucose. Milk is the most famous source of
Lactose. Used in infant formulations, and as a diluent in
pharmaceuticals
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Maltose Made up of two glucose molecules. Produced when amylase
breaks down starch.amylasestarch Obtained from malt sugar and when
glucose is caramelized.
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Polysaccharides
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Starch Starch or amylum is a carbohydrate consisting of a large
number of glucose units joined together by glycosidic
bonds.carbohydrateglucose glycosidic bonds produced by all green
plants as an energy storeplants It is the most common carbohydrate
in the human diet like potatoes, wheat, maize (corn),
rice.potatoeswheatmaizerice
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Cont, Starch consists of two types of molecules: the linear and
helical amylose and the branched amylopectin.helical
amyloseamylopectin Glycogen, the glucose store of animals, is a
more branched version of amylopectin. Used as an additive for food
processing, typically used as thickeners and stabilizers in foods
such as puddings, custards, soups, and salad dressings, and to make
noodles and pastas.food processing Depending on the plant, starch
generally contains 20 to 25% amylose and 75 to 80% amylopectin by
weight.
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Another view of amylose and amylopectin, the two forms of
starch. Amylopectin is a highly branched structure, with branches
occurring every 12 to 30 residues
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Glycogen Glycogen is also known as animal starch. It is stored
in muscle and liver tissue Complete hydrolysis yields glucose
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Glycogen is the glucose storage polymer in animals, is similar
in structure to amylopectin, but glycogen has more branches The
highly branched structure permits rapid release of glucose from
glycogen stores, i.e. in muscle during exercise. The ability to
rapidly mobilize glucose is more essential to animals than to
plants
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ASSIGNMENTS Students selected in the previous slide are
requested to prepare slides about any of the following topics and
delivered before next lecture: 1.Importance of carbohydrates in
human life. 2.Carbohydrates and cell membrane. 3. Carbohydrates in
plants. 4.Importance of glycogen. 5.Disease related to high glucose
level. 6.Disease related to low glucose level. 7.Polysaccharides.
8.Functions of glycoprotein. 9.Carbohydrate and energy.
10.Carbohydrate digestion.
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Students selected for assignment
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Study Questions: Mention the 4 major biomolecules of life.
Mention one classification of carbohydrates giving examples.
Explain why sucrose is a non reducing while maltose is a reducing
sugar