1. Lipids Review

2. Lipids 1. 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

3. Lipids 2. What do all lipids have in common?
Lipids are hydrophobic, which means that they repel water.
In other words…
Lipids are nonpolar, which means that they do not dissolve in water.

4. Lipids 3. What is the structure of a triglyceride?
Fatty acid tail
Glycerol
A triglyceride consists of three fatty acid tails bonded to a glycerol molecule
More specifically it looks like this:
Carbon atom
Hydrogen atom
Oxygen atom

5. Lipids 4. What molecule is released whenever a
fatty-acid tail bonds to glycerol?
(Click once and watch the animation)
Glycerol
Fatty acid tail
Fatty acid tail
Fatty acid tail
As you can see, a water molecule is released for each bond formed.

6. Lipids 5. What is the difference between saturated and
unsaturated fatty-acid tails?
Saturated fatty-acids have the maximum number of hydrogen atoms that each carbon in the chain can hold.
Carbon atom
Hydrogen atom
Oxygen atom

7. Lipids 5. What is the difference between saturated and
unsaturated fatty-acid tails?
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.
Carbon atom
Hydrogen atom
Oxygen atom

8. Lipids 5. What is the difference between saturated and
unsaturated fatty-acid tails?
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?
Carbon atom
Hydrogen atom
Oxygen atom

9. Lipids 5. What is the difference between saturated and
unsaturated fatty-acid tails?
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.
Carbon atom
Hydrogen atom
Oxygen atom

10. Lipids 6. How are fatty acids named?
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
Notice also that the double bond starts at the third carbon from the end of the chain.
In addition, the carbon atom at the end of a fatty acid is called the omega (Ω) carbon Ω
Therefore, the double bond position is referred to as omega-3 3
Carbon atom
Hydrogen atom
Oxygen atom

11. Lipids 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?
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
Carbon atom
Hydrogen atom
Oxygen atom

12. Lipids 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?
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. Ω 3 Ω
Carbon atom
Hydrogen atom
Oxygen atom

13. Lipids 8. 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 Ω 3 3 Ω
The bottom chain is a monounsaturated 12:1 omega-3 trans fat

14. Lipids 9. What would you call the top chain of this triglyceride?
The top chain is a polyunsaturated 12:2 omega-3 cis, -6 trans fat Ω 3 6 3 Ω
Carbon atom
Hydrogen atom
Oxygen atom

15. Lipids 10. How does a phospholipid differ from a triglyceride?
A triglyceride has three fatty-acid chains (remember, tri means 3).
Fatty acid tail
Glycerol
A phospholipid has two fatty-acid chains. The third chain has been replace by a PO4
(phosphate) group.
Glycerol
Fatty acid tail
PO4

16. Lipids 11. 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.

17. Lipids 12. 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)

18. Lipids 13. Where are phospholipids found in the body?
Phospholipids are found in cellular membranes, of which they are a major component.

19. Lipids 14. How do lipids behave when placed in water?
Both molecules will float in water as shown below.
The nonpolar tails are repelled by water…
Note: Lipid molecules are a million times smaller than shown.
…while the polar heads are attracted to water.

20. Lipids
15. What is the most common steroid in the body?
Cholesterol

21. Lipids 16. 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.
Asldosterone regulates blood pressure.
Cholic acid is involved in digestion.
Cortisol is a stress hormone.

22. Lipids 16. 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

23. Lipids 17. How do organisms use lipids?
Energy storage: Animals store lipids in fat cells as long-term energy storage.
Protection: The waxy coating on plant leaves help repel water.

24. Lipids 17. 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.

25. Camel humps are made of fat
Lipids
17. How do organisms use lipids?
Production of water:
Fatty acids produce a
lot of water when they
are used as fuel during
respiration.
Camel humps are made of fat
Construction: Bees use
wax (beeswax) to make
honeycombs.

26. Lipids 18. 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.

27. Lipids 19. 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.