3.3 Lipids

A tail has a kink wherever there is an unsaturated bond.

b. Because of their structure, phospholipids form a bilayer that serves as the major component of a cell's plasma membrane.

The C-H bonds of fatty acids make them a richer source of chemical energy that glycogen,

because more bonds with stored energy are present in fatty acids; in contrast glycogen has many C-OH bonds, which are less energetic bonds.

Also, fat droplets do not contain water,

because they are non polar.

By comparison, unsaturated fats Eem to help prevent CVD,

because they don't stick together in the blood and therefore don't clog arteries.

Waxes are solid at normal temperatures,

because they have a high melting point.

We are familiar with fats and oils,

because we use them in cooking and consume them as food.

However, increasingly they are also

being used as an alternative fuel source, such as biodiesel, for our industrialized societies.

If the same amount of energy were stored as glycogen, a

bird would be so heavy it would not be able to fly.

About 0.15g of fat per gram of

body weight is accumulated each day.

Honey contains the sugars fructose and glucose,

breakdown products of the sugar sucrose.

Small birds, such as the

broad-tailed hummingbird, store a great deal of fat before they start their long spring and fall migratory flights.

Unsaturated fats might be healthier for you,

but plant oils can easily go rancid and aren't solid at room temperature, which makes them more difficult to cook with and to use in solid food products.

Each type of steroid differs primarily

by the types of functional groups attached to the carbon skeleton.

Hydrogens bonded only

carbon are non polar and have no tendency to form hydrogen bonds with water molecules.

The cis or trans

configuration of an unsaturated fatty acid affects its biological activity.

Each fatty acid

consist of a long hydrocarbon chain with an even number of carbons and a -COOH (carboxyl) group at one end.

At on point, investigators thought that the total amount of lipid in the diet caused

coronary and other heart-related diseases.

The reason is that a double bond

creates a kink in the fatty acid chain that prevents close packing between the hydrocarbon chains.

As scientific evidence accumulated showing a

distinction between the effects of saturated and unsaturated fats, public perception changed.

Trans fat (red highlight) possess a

double bond with hydrogen atoms on either side of the carbon chain.

Saturated fatty acids have no

double bonds between the carbon atoms and contain as many hydrogens as they can hold.

When a fat or an oil forms, the -COOH functional groups of three fatty acids react with the -OH groups of glycerol

during a dehydration reaction, resulting in a fat molecule and three molecules of water.

Gram for gram, fat stores

energy than glycogen.

Cholesterol is an

essential component of an animals cell's plasma membrane, where it provides physical stability.

The next sections will

explore the structure and function of these classes of lipids.

To get around this problem,

food manufacturers hydrogenated unsaturated fatty acids by heating the oil and exposing it to hydrogen gas.

In many plants, waxes, along with other molecules

form a protective cuticle (covering) that prevents the loss of water from all exposed parts (Fig 3.13a).

Steroid molecules have skeletons of

four fused carbon rings.

Figure 3.10 Synthesis and degradation of a triglyceride. Following a dehydration reaction,

glycerol is bonded to three fatty acid molecules as fat forms and water is given off.

Nearly all animals use fat rather than

glycogen for long-term energy storage.

Diets high in animal fat

have been associated with circulatory disorders, because saturated fats and other molecules can accumulate inside the lining of blood vessels and block blood flow.

Unsaturated fatty acids

have double bonds in the carbon chain, which reduces the number of bonded hydrogen atoms.

In many animals, waxes are involved

in skin and fur maintenance.

In humans, wax is produced by glands

in the outer ear canal.

Trans fat consumption also appears to

increase risk of CVD and heart attack.

Glycerol

is a 3 carbon compound with three -OH.

A trans fat

is a triglyceride that has at least one bond in a trans configuration.

The fluidity of the plasma membrane

is affected by kinks in the phospholipids' tails.

The male sex hormone, testosterone,

is formed primarily in the testes, and the female sex hormone, estrogen, is formed primarily in the ovaries.

b. If here are double bonds between some of the carbons (yellow highlights,) the fatty acid

is unsaturated and a kink occurs in the chain.

A variety of organic compounds are classified as

lipids.(Gk. lips, "fat") (Table 3.3). These compounds are insoluble in water due to their hydrocarbon chains.

Waxes: In waxes,

long-chain fatty acids are connected to carbon chains containing alcohol functional groups.

The -OH groups are polar,

making glycerol soluble in water.

Fats

more formally called triglycerides, are the primary lipid used by animals for both insulation and long-term energy storage.

Triglycerides: Long-Term Energy Storage: Triglycerides are composed

of fatty acids and glycerol subunits.

This treatment made the otherwise liquid plant

oils semisolid at room temperature and gave foods containing partially hydrogenated oils better shelf life.

In addition, double bonds in unsaturated fatty acids may have chemical groups arranged

on the same side (termed cis configuration) or on opposite sides (termed trans configuration) of the double bond.

A honeybee produces beeswax in glands

on the underside of its abdomen.

Figure 3.13 Waxes. Waxes are a type of lipid. a. Fruits are protected by a waxy coating, which is visible

on these plums. b. bees secrete the wax that allows them to build a comb, where they store honey.

Testosterone and estrogen differ

only by the functional groups attached to the same carbon skeleton, yet each has its own profound effect on the body and sexuality of an animal.

As science has brought the negative effects of trans fats to light,

perception has changed once again.

When exposed to water,

phospholipids tend to arrange themselves so that the polar heads are oriented toward water and the non polar fatty acid tails are oriented away from water.

In living organisms, which are made mostly of water,

phospholipids tend to become a bilayer (double layer).

These hormones are

present in many living creatures.

It als traps dust and dirt,

preventing these contaminants from reaching the eardrum.

Science constantly refines what we know as new evidence

provides greater insight into how we function and live.

Health organizations have recommended

replacing fat with oils such as olive oil and cola oil in our diet whenever possible.

The fatty acid chins may be either

saturate or unsaturated.

Beeswax is used to make the

six-sided cells of the comb, where honey is stored.

The hydrophilic (polar) head is

soluble in water, whereas the two hydrophobic (non polar) tails are not.

Cholesterol is the precursor of several other steroids,

such as the sex hormones testosterone and estrogen.

Saturated fats are flat molecules

that easily stick together in the blood, and too much saturated fat has been shown by scientists to negatively affect heart health, contributing to clogging of arteries and cardiovascular disease (CVD).

The presence of cholesterol encourages

the accumulation of fatty material inside the lining of the blood vessels, which decreases the size of the opening and thereby can result in high blood pressure.

Nature of Science: Saturated and Trans Fats in Foods: You have probably heard that you should limit

the amount of saturated fats and trans fats in your diet.

Following a hydrolysis reaction,

the bonds are broken due to the addition of water.

Public outcry has prompted changes in

the food services industry, with clear labeling of trans fats on all food products and with more restaurants using trans fat-free oils during cooking.

The polar heads prefer to interact with

the water while the nonpolar tails associate together and stay away from water molecules.

Being hydrophobic,

they are also waterproof and resistant to degradation

Even though cooking oils and water are both liquid,

they do not mix, even after shaking, because the non polar oil and polar water are chemically incompatible.

Fat is distributed

throughout the body, but the majority is found just beneath the skin of most animals, where it helps retain body heat.

This is a good example of how our perceptions change over

time base scientific evidence, and it illustrates the essential role that science plays in the common good.

Cholesterol can also contribute

to circulatory disorders.

List the functions of triglycerides, phospholipids, steroids, and waxes.

triglycerides= store energy. Phospholipids= component of plasma membrane. Steroids= component of plasma membrane (cholesterol), sex hormones. Waxes= Protection, prevention of water loss (cuticle of plant surfaces), beeswax, earwax

Triglycerides containing fatty acids with

unsaturated bonds melt at a lower temperature than those containing only saturated fatty acids.

This phospholipid bilayer is a key component

used to keep cells separate from the biological compartments within cells.

This difference has applications

useful to living organisms. For example, the feet of reindeer and penguins contain unsaturated triglycerides, and this helps protect those exposed parts from freezing.

An unintended consequence of hydrogenation, however,

was the formation of trans fats.

But why? We know that saturated fats,

which come from animals and are solid at room temperature, have effects in the body that are different from this of unsaturated fats, which come from plants and are liquid at room temperature.

In general, fats,

which most often come from animals, are solid at room temperature, whereas oils, which come from plants, are liquid at room temperature.

Many commercially packaged foods contain trans fats,

which recently have been shown to increase LDL (sometimes called bad cholesterol) and lower HDL (sometimes called good cholesterol) levels in the blood.

This portion of the molecule becomes the polar head,

while the hydrocarbon chains of the fatty acids become the non polar tails.

Thus, phospholipids arrange themselves like a "sandwich,"

with the polar heads facing the outside (the bread slices) and the fatty acid tails on the inside (the filing).

Butter is a fat that is solid at room temperature and is composed primarily of saturated fatty acids

, whereas corn oil, which is a liquid even when placed in the refrigerator, is composed primarily of unsaturated fatty acids.

Glycerol

Three-carbon carbohydrate with three hydroxyl groups attached; a component of fats and oils.

Oils

Triglyceride, usually of plant origin, that is composed of glycerol and three fatty acids and is liquid in consistency due to many unsaturated bonds in hydrocarbon chains of the fatty acid.

Phospholipids: Membrane Components: Phospholipids

are basically triglycerides, except that in place of the third fatty acid attached to glycerol, there is a polar phosphate group.

In addition to the triglycerides, phospholipids, steroids, and waxes

are important lipids found in living organisms.

Steroids: Four Fused Rings: Steroids

are lipids with structures that are entirely different from those of triglycerides and phospholipids.

Triglycerides in plants are commonly referred to

as oils.

Most of the fatty acids in cells contain

16 or 18 carbon atoms per molecule, although smaller ones are also found.

A plasma membrane is essential to the structure of function of a cell,

and this signifies the importance of phospholipids to living organisms.

Lipids

Class of organic compounds that tend to be soluble in non polar solvents; includes fats and oils.

Cholesterol-lowering medications

are available.

Unsaturated fatty acids

Fatty acid molecule that contains double bonds between some carbons in its hydrocarbon chain; contains fewer hydrogens then a saturated hydrocarbon chain.

Saturated fatty acids

Fatty acid molecule that lacks double bonds between the carbon of its hydrocarbon chain. The chain bears the maximum number of hydrogens possible.

Contrast the structures of fats, phospholipids, and steroids

Glycerol is a 3-carbon compound with three -OH groups. The -Oh groups are polar, making glycerol soluble in water. When fat or an oil forms, the -COOH functional groups of three fatty acids react with the -OH groups of glycerol during dehydration reaction, resulting in a fat molecule and three molecules of water. Phospholipids are constructed like fats, except that in place of the third fatty acid, they have a polar phosphate group. The hydrophilic (polar) head is soluble in water, whereas the two hydrophobic (nonpolar) tails are not. A tail has a kink whenever there is an unsaturated bond. b. Because of their structure, phospholipids form a bilayer that serves as the major component of a cell's plasma membrane. The fluidity of the plasma membrane is affected by kinks in the phospholipids' tails. Steroid molecules have skeletons of four fused carbon rings. Each type of steroid differs primarily by the types of functional groups attached to the carbon skeleton.

How would you balance the needs of the food industry with the health risks associated with changing the chemical composition of a food?

I would go with the unsaturated fats just because they are healthier, although they still can cause harm unsaturated fats don't do that much damage to your arteries.

Compare the functions of phospholipids and steroids in cells.

In cells the phospholipid bilayer is keeps the outside environment from the inside of the cell. It makes up the plasma membrane. Cholesterol is an essential component of an animal cell's plasma membrane, where it provides physical stability. Cholesterol is the precursor of several other steroids, such as the sex hormones testosterone and estrogen.

Describe why lipids are essential to living organisms.

Lipids are important to organisms because they help us maintain heat and store energy.

Fatty acid

Molecule that contains a hydrocarbon chain and ends with an acid group.

Phospholipids

Molecule that forms the bilayer of the cell's membranes; has a polar, hydrophilic head bonded to two nonpolar, hydrophobic tails.

Triglycerides

Neutral fat composed of glycerol and three fatty acids; typically involved in energy storage.

Fats and oils are degraded during a hydrolysis reaction.

Notice that triglycerides have many non polar C-H bonds; therefore, they do not mix with water.

Fats

Organic molecule that contains glycerol and three fatty acids; energy storage molecule.

Explain why phospholipids form a bilayer in water.

Phospholipids have hydrophilic heads and hydrophobic tails. When exposed to water, phospholipids tend to arrange themselves so that the polar heads are oriented toward water and the non polar fatty acid tails are oriented away from water.

What is the chemical structure of a trans fat compared to that of a non-trans fat?

Saturate fats are solid at room temperature, Unsaturated are liquid at room temperature.

Contrast the structure of a saturated fatty acid with that of an unsaturated fatty acid.

Saturated fatty acid has no double bonds Unsaturated fatty acid has double bonds and a trans bond.

Distinguish between saturated and unsaturated fatty acids.

Saturated is solid at room temperature and unsaturated is liquid at room temperature. Saturated fats are more harmful to health, unsaturated fats can be harmful but aren't as damaging to arteries as saturated fats.

The plasma membrane that surrounds cells consist primarily of a phospholipid bilayer.

The presence of kinks in the tails causes the plasma membrane to be fluid across a range of temperatures found in nature.

Steroids

Type of lipid molecule having a complex four carbon rings-e.g., cholesterol, estrogen, progesterone, and testosterone.

trans fat

Unsaturated fatty acid chain in which the configuration of the carbon-carbon double bond is such that the hydrogen atoms are across from each other, as opposed to being on the same side (cis).

Notice in Figure 3.11a that

a double bond causes a tail to kink.

Figure 3.12 Steroid diversity.

a. Built like cholesterol, (b) testosterone and (c) estrogen have different effects on the body due to different functional groups attached to the same carbo skeleton.

Figure 3.9 Saturated and unsaturated fatty acids. A fatty acid has a carboxyl group attached to a long hydrocarbon chain.

a. If there are no double bond between the carbons in the chain, the fatty acid is saturated.

Figure 3.11 Phospholipids from membranes.

a. Phospholipids are constructed like fats, except that in place of the third fatty acid, they have a polar phosphate group.

Testosterone is the male sex hormone

active in peacocks (left), and estrogen is the female sex hormone active in peahens (right).

Earwax contains ceramic,

an organic compound that, at the very least, repels insects and in some cases even kills them.

Phospholipids have hydrophilic heads

and hydrophobic tails.

Human and plant estrogens are similar in structure,

and if estrogen therapy is recommended, some women prefer taking soy products in preference to estrogen from animals.

Until recently, trans fats were of little cancer to the general public,

and people readily consumed them without much thought.