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MO Figure
Lipids
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Topics Covered in this Module
Understanding Lipids
Major Objectives of this Module
Describe the main characteristics of lipids.
Distinguish among triacylglycerol, saturated fatty acid, and
unsaturated fatty acid.
Relate the structure of fat molecules to the function of energystorage.
Explain why phospholipids form bilayers and relate the structure
of phospholipids to cell structure and function.
Describe the structure and basic function of steroids.
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Understanding lipids
Diverse class of biological molecules Wide range of structures and functions
Do not mix well with water
Fats, phospholipids and steroids
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A fatty acid consists of a
carboxyl group attached to
a long carbon skeleton
(even numbered, usually
between 14 and 22)
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Figure 1b Phospholipid
In a phospholipid, two fatty
acids and a phosphate groupare attached to glycerol
The two fatty acid tails are
hydrophobic, but the
phosphate group and itsattachments form a
hydrophilic head
Amphipathic (hydrophobic +
hydrophilic)
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Phospholipids form micelles and
bilayers
Circular, single-layered.
Short tailed more likely to form
these.
Small objects that formnaturally when the
hydrophobic phospholipid tail
points inward, protecting the
phospholipid tail from the
water.
Aid in transport & absorption
of complex lipids & fat-soluble
vitamins (e.g., Vitamin A).
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Phospholipid bilayer
In water, hydrophobic ends of phospholipids
align with one another, preventing themfrom interacting with water.
Hydrophilic heads are in contact with
environmental aqueous solutions.
This arrangement produces a phospholipid
bilayer. Provides boundary protecting cells from
their outside environment.
Controls what materials enter or leave the
cell.
Nonpolar molecules easily pass through the
cellular membrane, polar (hydrophilic)
molecules need help
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Steroids
Sterols are steroids with apolarOH group on oneend, and a non-polarhydrocarbon on the otherend.
They are amphipathic.
Functional groups
4 fused rings
(6,6,6,5)
Cholesterol
Steroids are lipids characterized by a carbon skeleton
consisting of four fused rings
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Estradiol
Testosterone
Male lion
Female lion
Steroid hormones control
development, behavior, and
biochemical processes.
Steroid hormones are
derived from cholesterol.
other hormones are
peptides
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Figure 5
Important for biological functions in animal cell membranes.
Liver produces cholesterol but can also be obtained from diet.
Lipoproteins transport cholesterol through the bloodstream.Lipoproteins have internal hydrophobic regions and hydrophilic exteriors.High-density lipoprotein (HDL): carriesgood cholesterol out of the blood tothe liver where it can be reused by the body.Low-density lipoprotein (LDL): carriesbad cholesterol,from liver to body.
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Figure 7
Fats
Store chemical
energy.
Hydrophobic,
no affinity for
water.
Also called a
triacylglycerol
(or a
triglyceride).
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Saturated fatty acids
Linear structure allowsfatty acid chains to pack
together closely.
As a result are often
solid at room
temperature.
Mammalian fats such
as lard and butter have
a high content of
unsaturated fat.
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Unsaturated fatty acids
Almost always in a cis
formation, which produces a
kink in the molecule. This
prevents fatty acids from
packing tightly together. Also referred to as an oil.
From plants and animals
such as olive oil and cod liver
oil.
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Trans fats
Unsaturated fats with a trans double bond; allows for a more densearrangement of fat molecules, so they remain solid at room
temperature.
Most are man-made, from commercial hydrogenation of oils. It
changes the texture and shelf-life, but is not natural and it isunhealth : it increase LDL cholesterol which is linked to heart
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Essential fatty acids
Liver cannotproduce alltypes of fattyacids the body
needs, mustcome from diet.These includeomega-3 and
omega-6 fattyacids.
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Its the balance of omega 3 and omega
6 in our bodies that is key to good
health.
Diets rich in omega 3s correlate with
reduced cardiovascular disease, andpossibly reduced cancer as well.
Sources: fish; eggs, milk and cheese
from grass-fed chickens and cows.
Omega 6s are converted to mediators
of immune/inflammatory responses,
which damage tissue over time
(vascular, asthma, arthritis, etc).
Sources: plant oils
Some fats are actually good for you! Omega-3
polyunsaturated fats (PUFAs)
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Animal energy storage
Animals store energy in fats.
Fat compounds hold twice as much energy aspolysaccharides.
Animals require a more compact energy source. Adipose cells are cells that store fat.
Swell and shrink as reserves are stored and used.
Also cushion bodily organs and provide insulation. Consuming more calories than needed may lead to
increased adipose tissue and more fat storage overall,
which can in turn lead to high triglyceride levels.
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Summary
OBJECTIVE Describe the main characteristics of lipids.
Lipids include fats, phospholipids, and steroids. Most lipids are composed
primarily of hydrocarbons held together with single and/or double bonds. They
are nonpolar and hydrophobic, and they do not interact with water. Lipids containfunctional groups that are polar in nature. These functional groups are hydrophilic
and interact with water, however the majority of a lipid is nonpolar and
hydrophobic.
OBJECTIVE Distinguish among triacylglycerol, saturated fatty acid, and
unsaturated fatty acid.
Fats, also known as triacylglycerols, can be constructed of saturated fatty acids
and/or unsaturated fatty acids. A triacylglycerol forms when a hydroxyl on the
carboxyl functional group combines with the hydrogen on the hydroxyl functional
group on the glycerol. This pairing forms an ester link joining the fatty acid to the
glycerol. Two more fatty acids join the glycerol to produce the triacylglycerol. In asaturated fatty acid, the carbons in the hydrocarbon tail are bonded by single
covalent bonds, which makes them saturated with hydrogen atoms. In an
unsaturated fatty acid, the hydrocarbon tail contains one or more double covalent
bonds between the carbons. The fatty acid's carbon skeleton is not saturated
with hydrogen atoms.
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OBJECTIVE Relate the structure of fat molecules to the function of energy
storage.
Plants use polysaccharides, like starch, as energy reserves. These compounds are
large. In contrast, lipids are relatively smaller molecules that hold twice as much
energy as polysaccharides. Animals need lipids such as triacylglycerols to continueto maintain life functions. Animals store triacylglycerols in adipose tissues that
shrink and swell as reserves are used or stored. Adipose tissue has additional
benefits of cushioning major organs and providing insulation. Fat is generally
synonymous with the term lipid, and the characteristics of fat molecules
(triacylgycerols) can be applied to all lipids. Steroids and phospholipids, like fats,
are molecules used for energy storage.
OBJECTIVE Explain why phospholipids form bilayers and relate the structure of
phospholipids to cell structure and function.
Phospholipids are composed of a glycerol bound to two fatty acids and one
phosphate functional group. The hydrocarbon tails of fatty acids are hydrophobic
and do not interact with water. The phosphate functional group is hydrophilic andinteracts with water. When placed in water, the phospholipids align with the
phospholipid tails facing each other and exposing the phospholipid head to the
outside environment. They can form a micelle or a bilayer. The bilayer structure is
important because it produces a cell membrane. The membrane controls what
materials can enter or leave the cell; it separates and defines the inner cell from
the outside environment.
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OBJECTIVE Describe the structure and basic function of steroids.
A steroid consists of a carbon skeleton composed of four fused rings. Steroids such
as sex hormones and cholesterol are necessary for life functions. In particular,
cholesterol is essential for the body to construct more complex steroid molecules.
Cholesterol is produced by the liver or obtained from foods. Doctors monitor thelevel of certain cholesterol components in human blood. HDL offers positive
health benefits. Doctors check the levels of HDL and LDL in blood to monitor the
patient for atherosclerosis.