Lipids Review

Lipids1. List four substances that are lipids.

Triglycerides (fats & oils)

Phospholipids (a component of cell membranes)

Waxes (waxy coating on leaves, candle wax, bees wax)

Cholesterol and Steroids

Lipids2. What do all lipids have in common?

Lipids are hydrophobic, which means that they repel water.

Lipids are nonpolar, which means that they do not dissolve in water.

In other words…

Lipids3. What is the structure of a triglyceride?

More specifically it looks like this:

Carbon atomHydrogen atom

Oxygen atom

Fatty acid tail

Fatty acid tail

Fatty acid tail

Gly

cero

l A triglyceride consists of three fatty acid tails bonded to a glycerol molecule

Gly

cero

l

Lipids4. What molecule is released whenever a fatty-acid tail bonds to glycerol?

As you can see, a water molecule is released for each bond formed.

Fatty acid tail

Fatty acid tail

Fatty acid tail

(Click once and watch the animation)

Lipids5. What is the difference between saturated and unsaturated fatty-acid tails?

Carbon atomHydrogen atom

Oxygen atom

Saturated fatty-acids have the maximum number of hydrogen atoms that each carbon in the chain can hold.

Lipids5. What is the difference between saturated and unsaturated fatty-acid tails?

Carbon atomHydrogen atom

Oxygen atom

For example, count the number of white hydrogen atoms in the middle fatty acid chain.

You should have counted 23. That is the maximum number that chain can hold.

Lipids5. What is the difference between saturated and unsaturated fatty-acid tails?

Carbon atomHydrogen atom

Oxygen atom

Now count the number of hydrogen atoms in the top chain.

You should have counted 21. That is two atoms less than the middle chain. Can you figure out why?

Lipids5. What is the difference between saturated and unsaturated fatty-acid tails?

Carbon atomHydrogen atom

Oxygen atom

If you thought it had something to do with the double bond (see circled area) you are correct. When a pair of carbon atoms form a double bond, two hydrogen atoms are released. The chain is now said to be unsaturated.

Lipids6. How are fatty acids named?

Carbon atomHydrogen atom

Oxygen atom

In addition, the carbon atom at the end of a fatty acid is called the omega (Ω) carbon

Notice also that the double bond starts at the third carbon from the end of the chain.

Therefore, the double bond position is referred to as omega-3

The top fatty acid chain has 12 carbon atoms and 1 double bond. It is also unsaturated, so its referred to as mono-unsaturated 12:1

3

Ω

Lipids7. Notice that both the top chain and bottom chain contain an omega-3 double bond. However, the top chain has a kink in it but not the bottom chain. What do you think causes the kink?

Carbon atomHydrogen atom

Oxygen atom

When the hydrogen atoms end up on the same side of the double bond they repel each other, causing a kink in the chain. This is known as a cis configuration.

Ω

3

3 Ω

Lipids

Carbon atomHydrogen atom

Oxygen atom

When the hydrogen atoms end up on opposite sides of the double bond the shape of the chain remains unchanged (see circled area). This is known as a trans configuration.

7. Notice that both the top chain and bottom chain contain an omega-3 double bond. However, the top chain has a kink in it but not the bottom chain. What do you think causes the kink?

Ω

3 Ω

Lipids8. So how would you name each of the fatty-acid tails?

The top chain is a monounsaturated 12:1 omega-3 cis fat

The middle chain is a saturated 12:0 fat

The bottom chain is a monounsaturated 12:1 omega-3 trans fat

3

3

Ω

Ω

Lipids9. What would you call the top chain of this triglyceride?

Carbon atomHydrogen atom

Oxygen atom

The top chain is a polyunsaturated 12:2 omega-3 cis, -6 trans fat

36

3

Ω

Ω

Lipids10. How does a phospholipid differ from a triglyceride?

A triglyceride has three fatty-acid chains (remember, tri means 3).

Gly

cero

l

Fatty acid tail

Fatty acid tail

PO4

Fatty acid tail

Fatty acid tail

Fatty acid tailG

lyce

rol

A phospholipid has two fatty-acid chains. The third chain has been replace by a PO4

(phosphate) group.

Lipids11. What is the simplest way to draw triglycerides and phospholipids?

Triglycerides are usually drawn like this.

In phospholipids, the phosphate group usually has another molecule attached to it. Therefore the phosphate head is drawn as a large circle.

Lipids12. Are triglycerides and phospholipids polar or nonpolar?

Both molecules have a polar and nonpolar regions

Polar heads which are hydrophilic (water loving)

Nonpolar tails which are hydrophobic (water fearing)

Lipids13. Where are phospholipids found in the body?

Phospholipids are found in cellular membranes, of which they are a major component.

Lipids14. How do lipids behave when placed in water?

Both molecules will float in water as shown below.

The nonpolar tails are repelled by

water…

…while the polar heads are attracted

to water.

Note: Lipid molecules are a

million times smaller than shown.

Lipids15. What is the most common steroid in the body?

Cholesterol

Lipids16. Why is cholesterol biological important?

a. The body uses cholesterol as a starting point to make other steroids, like the ones shown below.

For example: progesterone, estradiol, and testosterone

are sex hormones.

Cortisol is a stress

hormone.

Asldosterone regulates

blood pressure.

Cholic acid is involved

in digestion.

Lipids16. Why is cholesterol biological important?

b. Cholesterol is also found in the lipid bilayer of cell membranes. It regulates membrane permeability and fluidity over a wide range of temperatures.

Cholesterol molecule

Lipids17. How do organisms use lipids?

a. Energy storage: Animals store lipids in fat cells as long-term energy storage.

b. Protection: The waxy coating on plant leaves help repel water.

Lipids17. How do organisms use lipids?

c. Buoyancy for marine animals: lipids are less dense than water helping animals float.

d. Insulation: A layer of fat beneath the skin cuts down on heat loss.

Lipids17. How do organisms use lipids?

e. Production of water: Fatty acids produce a lot of water when they are used as fuel during respiration. Camel humps are made of fat

f. Construction: Bees use wax (beeswax) to make honeycombs.

Lipids18. Which provides more energy per gram, fats or carbohydrates?

Fats will give off more energy (over twice as much) than will carbohydrates. Generally, fats provide about 9 Calories per gram and carbohydrates provide about 4 Calories per gram.

Lipids19. Which provides the quickest release of energy in the body, fats or carbohydrates?

Small carbohydrates like table sugar provide energy very quickly. Complex carbohydrates like starches and glycogen release energy more steadily but at a slower pace. Fats make energy available at a much slower pace than carbohydrates.