Question 1

The stimulation of fatty acid biosynthesis in the liver is achieved by:

Accepted Answer

Acetyl-CoA carboxylase is the important regulated enzyme of fatty acid biosynthesis.Insulin plays a role in its dephosphorylation.

Question 2

A patient complains about frequent aches and pains in his muscles.A blood test shows increased levels of creatine kinase MM, fatty acids and also myoglobin.A second blood sample, this time taken after an overnight fast, revealed low levels of blood glucose and elevated VLDL.This patient most likely has which of the following conditions?

Accepted Answer

Elevated fatty acid levels suggest a defect in fatty acid oxidation.Muscles need fatty acids for contraction, and the liver needs them during fasting, to produce the ATP for gluconeogenesis.Therefore, muscle weakness, muscle damage on exertion, and hypoglycemia during fasting are typical for generalized defects in carnitine shuttle or b-oxidation.

Question 3

Ketone bodies can be used as a source of metabolic energy by most tissues.One tissue that cannot oxidize ketone bodies is:

Accepted Answer

The liver makes ketone bodies but does not oxidize them.

Question 4

A deficiency of which of the following proteins is least likely to impair the utilization of adipose tissue triglyceride for ATP production in muscle tissue?

Accepted Answer

Acetyl-CoA carboxylase is needed for fatty acid biosynthesis.All other enzymes are needed for one or another step in fatty acid oxidation.

Question 5

A 23-year-old woman has just eaten a meal consisting mainly of carbohydrates.Which of the following best describes the activity of LPL and hormone-sensitive lipase (HSL) in adipose tissue of this individual?

Accepted Answer

Insulin increases capillary LPL in adipose tissue and strongly inhibits HSL.

Question 6

After a carbohydrate meal you can expect to find a high activity of _____ and low plasma levels of _____.

Accepted Answer

The activity of adipose tissue LPL is increased by insulin after a high-carbohydrate meal.However, plasma free fatty acid levels are low because there is little substrate for LPL, and the hormone-sensitive lipase is inhibited by insulin.

Question 7

A student who lives on only soft drinks and chocolate bars will have very little ẞ-oxidation of fatty acids in his liver.Why?

Accepted Answer

Dietary carbohydrate releases insulin, insulin activates acetyl-CoA carboxylase, and the malonyl-CoA formed by this enzyme inhibits the carnitine shuttle.The body does not need to oxidize fatty acids when carbohydrates are plentiful.

Question 8

Epinephrine acts by phosphorylating and activating hormone-sensitive lipase in a matter of minutes.One hormone that can facilitate lipolysis in the long term by stimulating the synthesis of the enzyme is:

Accepted Answer

As a long-acting stress hormone that works by regulating gene expression, cortisol creates the conditions under which the fast-acting stress hormone epinephrine can mobilize stored energy reserves.

Question 9

In adipocytes, protein kinase A activates lipolysis by phosphorylating two proteins.These proteins are:

Accepted Answer

Phosphorylation activates the hormone-sensitive lipase, and it removes perilipin from the surface of the fat droplet.

Question 10

A patient presents with low blood levels of glucose and ketones in plasma during fasting, accompanied by a high level of plasma free fatty acids.A urine analysis reveals high levels of dicarboxylic acids.The patient is most likely to benefit from:

Accepted Answer

This is a defect in b-oxidation.The high dicarboxylic acid levels are suggestive of medium-chain acyl-CoA dehydrogenase deficiency, rather than a defect of the carnitine shuttle.This condition leads to fasting hypoglycemia because gluconeogenesis requires adenosine triphosphate (ATP) from fatty acid oxidation during fasting, both for its energy requirement and as an activator of pyruvate carboxylase.

Question 11

A patient presents with low blood levels of glucose and ketones in plasma accompanied by high fatty acid levels.A urine analysis reveals high levels of dicarboxylic acids.This patient will most likely benefit from:

Accepted Answer

Dicarboxylic acids are formed by microsomal ω-oxidation from medium-chain fatty acids.Therefore, the dicarboxylic acids suggest that the patient has medium-chain acyl-CoA dehydrogenase deficiency, rather than a defect in the carnitine shuttle.Regular carbohydrate intake is important for preventing fasting hypoglycemia.

Question 12

The oxidation of fatty acids in the liver during fasting produces large amounts of acetyl-CoA, the reduced form of nicotinamide adenine dinucleotide (NADH), and ATP.All of these products affect carbohydrate metabolism by:

Accepted Answer

Through this mechanism, fatty acid oxidation takes precedence over carbohydrate oxidation during fasting.

Quiz 23: The Metabolism of Fatty Acids and Triglycerides