1. Which diet listed below would result in the production of ketone bodies in a healthy individual?
a. A diet rich in carbohydrates and very low in fat
b. A diet rich in fats and very low in carbohydrates
c. A diet rich in carbohydrates and very low in protein
d. A diet rich in protein and very...
1. Which diet listed below would result in the production of ketone bodies in a healthy individual?
a. A diet rich in carbohydrates and very low in fat
b. A diet rich in fats and very low in carbohydrates
c. A diet rich in carbohydrates and very low in protein
d. A diet rich in protein and very low in fat
Answer: B. Many of our cell- and tissue-types cannot use fatty acids as a fuel source for making ATP because they
lack the capacity to carry out beta-oxidation of fatty acids. When our only (or major) source of energy is fatty acids,
the liver will do the job of breaking them down into acetyl CoA for those cells that cannot do it for themselves.
However, owing to differences between the chemistry of the blood versus the chemistry of the insides of our cells,
we cannot ship acetyl CoA through the bloodstream. Therefore, the liver will assemble the excess acetyl CoA it
produces (from beta-oxidation of fatty acids) into the ketone bodies, acetoacetate, and 3-hydroxybutyrate. You can
think of ketone bodies as transport forms of acetyl units that can travel through the bloodstream and be taken up
by those cells that cannot break down fatty acids.
Those cells will convert the ketone bodies back to acetyl CoA and use that to keep their citric acid cycles going so
they can keep making ATP and stay alive. This, after all, is the whole point of this exercise - to enable us to survive
when our only energy source is fatty acids.
For the answer choice “A diet rich in carbohydrates and very low in fat”, again, remember that all of our cells can
use carbohydrates as fuel via glycolysis. There is no need to produce ketone bodies when carbohydrates are
abundant. Also bear in mind that we make ketone bodies from the catabolism (breakdown) of fatty acids by beta-
oxidation. If our diet were low in fat (= fatty acids), we wouldn’t have the starting material for ketone body
production. Therefore, this answer doesn’t work for two reasons.
2. What stimulates beta-oxidation of fatty acids?
a. The insulin signal
b. Low blood lipid levels
c. The glucagon signal
d. High blood glucose concentrations
Answer: C. Glucagon is the hormone that signals the hungry state. It tells us that our blood sugar level is too low
and that we are fasting or starving and need energy. Thus, glucagon signaling switches cells (especially liver cells) to
a program of releasing stored energy. It stimulates the breakdown of our storage molecules (glycogen,
triglycerides, and fatty acids.)
3. If a person were eating an absolutely fat-free diet, which vitamins would he or she not get enough
of?
a. Vitamins A, D, E, and K
b. Vitamins A, C, E, and K
c. Vitamins A, B, C, and D
d. Vitamins A, C, D, and K
Answer: A. It is important to recall that there are just four fat-soluble vitamins. All the other vitamins that we need
in our diet are water-soluble molecules. The fat-soluble vitamins are A, D, E, and K. If we consume no fats in our
diet, we will have no source for these vitamins, since they come in along with the fat we consume.
,4. What is a function of this molecule?
a. It is a hormone.
b. It is used to store energy.
c. It is used to maintain membrane fluidity.
d. It is used to make nucleic acids.
Answer: C. In the membranes of our cells, cholesterol acts in a manner similar to antifreeze in our cars’ radiators. If
we add antifreeze to our coolant, the coolant will freeze at a lower temperature and boil at a higher temperature
than it otherwise would, all by itself. That is to say, antifreeze EXPANDS the range over which the coolant stays
liquid.
Cholesterol has the same effect on our cell membranes, expanding the range over which they remain fluid. The
presence of cholesterol in our membranes means that they freeze at lower temperatures and melt at higher
temperatures than they would without cholesterol. In fact, this function is so crucial that if we did not have any
cholesterol, we would die. Luckily, we chordates (~vertebrates) can make all the cholesterol we need so we never
need to eat any.
For the answer choice “It is a hormone”, bear in mind that cholesterol itself is not a hormone. It is used, however,
as the basis to make many important hormones, called the steroid hormones. These include the sex hormones
such as estrogen and testosterone, and others, such as aldosterone, cortisone, and cortisol.
a. Phospholipid
b. Eicosanoid
c. Triglyceride
d. Cholesterol
Answer: C. The key to recognizing a triglyceride is to remember that a triglyceride has three (3) fatty tails attached
to a backbone of glycerol. Those three fatty tails are what the “tri” in triglyceride refers to. The “glyceride”,
obviously, refers to glycerol. In this course, the only molecules we encounter that have three fatty tails are the
triglycerides.
, Remember that a phospholipid only has two fatty tails. The third position of the glycerol backbone has a phosphate
group attached to it (recognizable by the “P” for the phosphorus atom, surrounded by four ‘O’s for oxygen atoms).
This is shown here.
6. If a fish raised in cold water were moved to much warmer water, how would it alter its membrane
phospholipids?
a. Membrane phospholipids would include more shorter-chain, unsaturated fatty acids.
b. It would add more cholesterol to its membranes.
c. Membrane phospholipids would include more longer-chain, saturated fatty acids.
d. Membrane phospholipids would include the same fatty acids under either condition.
Answer: C. The key to this question is to understand the relationship between the physical/chemical properties of
fatty acids and the fluidity of membranes. An important thing to understand about cell membranes is that they are
fluid. They are neither solid nor liquid, really, but something in between, almost like a gel. This fluidity allows the
things in the membrane, such as membrane proteins, cholesterol, and phospholipids to move around and this
movement is essential for staying alive.
If we were to suddenly move a goldfish (for example) from freezing water (0 degrees Celsius) to a summertime
pond (say, 25 degrees Celsius), that would be a huge problem. This is because the membrane lipids that were
appropriately fluid at 0 C will now be TOO liquid at the warmer 25 C. The same is true going the other way too. A
membrane that was appropriately fluid at 25 C would suddenly ‘freeze-up’ and become too solid at 0 C.
The bulk of the material that makes up our cell membranes are the fatty acids that are part of the phospholipids
from which the membrane is made. We can get a good idea of how temperature will affect membrane fluidity if we
remember how temperature affects fatty acid fluidity. A basic relationship you will want to remember is this: The
longer a fatty acid molecule is, the higher its melting point. The more double bonds it has, the lower it’s melting
point.
What this means for membrane fluidity is this: When it’s warm outside, and we want our membrane not to get too
“runny”, we want to make our phospholipids with more saturated, longer chain fatty acids. By contrast, when it is
colder, we want to use more shorter-chain and unsaturated fatty acids in our phospholipids to keep our membrane
from freezing solid.
7. What is the correct chemical formula of the following fatty acid?
a. CH3(CH2)3CH=CH(CH2)3CH=CH(CH2)3CH=CH(CH2)7COOH
b. CH3(CH2)4CH=CH(CH2)4COOH
c. CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH
d. CH3CH2H=HCH2C=CCH2C=C(CH2)7COOH
Answer: C. The formula ‘CH3(CH2)3CH=CH(CH2)3CH=CH(CH2)3CH=CH(CH2)7COOH’, indicates three (3) groups between
the CH3 and the first CH=CH, but our structure has only one there. Count carefully!
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