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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.