Question 1

The elongation of fatty acids occurs

Accepted Answer

The elongation of fatty acids occurs in both mitochondria and microsomes. Mitochondria elongate long-chain fatty acids, producing even longer fatty acids or precursors for synthesis of complex lipids. Microsomes are another important site of fatty acid elongation, particularly for shorter chain fatty acids. The cytosol plays a role in fatty acid synthesis but not elongation specifically. The brain is not directly involved in the process of fatty acid elongation.

Question 2

The maximal velocity (Vmax) of the acetyl-CoA carboxylase reaction would be obtained when

Accepted Answer

Vmax is the maximum rate of an enzyme-catalyzed reaction when all active sites of the enzyme are fully occupied with substrate. This condition is achieved when the concentration of the substrates, acetyl-CoA, carbon dioxide, and ATP are all saturating. Therefore, choice B is the best answer.

Question 3

Which of the following is an intermediate in fatty acid synthesis in the cytoplasm?

Accepted Answer

Malonyl-CoA is an intermediate in fatty acid synthesis in the cytoplasm.

Question 4

Oxidation of an odd-numbered chain fatty acid can be expected to yield proportionately less ATP than that of an even-numbered chain fatty acid because

Accepted Answer

The oxidation of propionyl-CoA, which is produced from odd-numbered fatty acids, requires an ATP-dependent carboxylation step to convert it into succinyl-CoA, thus consuming ATP and reducing the net ATP yield.

Question 5

All of the following conditions or factors would promote de novo fatty acid synthesis EXCEPT

Accepted Answer

A high glucagon/insulin ratio promotes the mobilization of stored fats and inhibits de novo fatty acid synthesis, as glucagon signals the need for energy mobilization, while insulin promotes energy storage and synthesis, including fatty acid synthesis.

Question 6

Acetoacetate is NOT oxidized to C02 in

Accepted Answer

The liver produces acetoacetate but does not oxidize it to CO2 because it lacks the necessary enzymes for ketone body utilization.

Question 7

The most prevalent saturated fatty acid in animal fat is

Accepted Answer

Palmitic acid is the most prevalent saturated fatty acid in animal fat, comprising around 25-30% of the total saturated fatty acids. Myristic acid is the second most prevalent, comprising around 14-16%. Caprylic and lauric acid are shorter chain fatty acids and are found in smaller amounts in animal fat. Stearic acid is also a saturated fatty acid but is more prevalent in plant sources of fat.

Question 8

Which of the following participates with human palmitate synthase as part of the same polypeptide chain?

Accepted Answer

Human palmitate synthase is part of the fatty acid synthase complex, where acyl carrier protein (ACP) plays a crucial role in the elongation of the fatty acid chain by carrying the growing fatty acid as it is being synthesized. This process occurs on the same polypeptide chain as the palmitate synthase activity, making ACP the correct answer.

Question 9

Metabolic cleavage of acetoacetyl-CoA to two molecules of acetyl-CoA is catalyzed by a

Accepted Answer

Thiolase catalyzes the cleavage of acetoacetyl-CoA to form two molecules of acetyl-CoA. This enzyme plays a key role in the degradation of ketone bodies and fatty acids in the mitochondria. Dehydrogenases are enzymes that oxidize substrates by removing hydrogen atoms. Hydratases catalyze the addition of water molecules to double bonds. Synthetases are enzymes that catalyze the formation of new bonds using energy from ATP. Racemases are enzymes that catalyze the conversion of stereoisomers from one form to another.

Question 10

The mobilization of triglyceride fatty acids from adipose tissue and their subsequent oxidation by muscle mitochondria involves all of the following EXCEPT

Accepted Answer

Acyl carrier protein is not required for the mobilization and oxidation of triglyceride fatty acids. The other four factors, serum albumin, carnitine, hormone sensitive lipase, and acyl-CoA synthetase, are all involved in the process.

Question 11

Considering the principal pathways involved, how many of the carbon atoms of glucose could maximally contribute to the net synthesis of fatty acid?

Accepted Answer

During fatty acid synthesis, each acetyl-CoA molecule contributes two carbon atoms to the growing fatty acid chain. The process begins with the conversion of glucose to acetyl-CoA via glycolysis and the citric acid cycle. From one molecule of glucose, two molecules of pyruvate are produced during glycolysis. These pyruvate molecules are then decarboxylated and oxidized, producing two molecules of acetyl-CoA that can be used for fatty acid synthesis. Therefore, only the carbons derived from these two acetyl-CoA molecules (4 carbons in total) can contribute to the net synthesis of fatty acids, making answer B the correct choice.

Question 12

Which enzyme or process requires the presence of acetyl-CoA in the cytosol?

Accepted Answer

ATP: citrate lyase is involved in the process that requires the presence of acetyl-CoA in the cytosol, as it cleaves citrate into oxaloacetate and acetyl-CoA, which is a crucial step in the synthesis of fatty acids and cholesterol in the cytosol.

Question 13

An increased synthesis of acetoacetate and 3-hydroxybutyrate by the liver

Accepted Answer

The increased synthesis of acetoacetate and 3-hydroxybutyrate by the liver is sustained by increased triacylglycerol hydrolysis in adipose tissue. This process releases fatty acids that are then taken up by the liver and converted to ketone bodies (acetoacetate and 3-hydroxybutyrate). This is a response to decreased glucose availability, such as during prolonged fasting or a low-carbohydrate diet, and provides an alternative metabolic fuel source for the brain and other tissues.

Question 14

Triglycerides

Accepted Answer

Triglycerides represent the main component of storage lipids, are composed of three fatty acids in ester linkage to a glycerol molecule, and are the most abundant members of the acyl glycerols or neutral fats. Therefore, all of the other answers are correct.

Question 15

The conversion of n moles of acetyl-CoA to 1 mole of palmitoyl-CoA (C16:0) requires

Accepted Answer

The conversion of n moles of acetyl-CoA to 1 mole of palmitoyl-CoA (C16:0) requires 7 moles of ATP. This is because palmitoyl-CoA synthesis involves seven rounds of condensation reactions, with each cycle requiring one molecule of acetyl-CoA and one molecule of malonyl-CoA. The conversion of malonyl-CoA to acetyl-CoA involves several steps that require ATP hydrolysis. Therefore, a total of 7 ATP molecules are consumed during the conversion of n moles of acetyl-CoA to 1 mole of palmitoyl-CoA (C16:0).

Question 16

The process of long chain fatty acid oxidation in liver is regulated in part by the interaction of

Accepted Answer

The regulation of long chain fatty acid oxidation in the liver is mainly controlled by the malonyl-CoA-Carnitine acyltransferase complex, which is composed of two enzymes: Carnitine acyltransferase I (CAT I) and Carnitine acyltransferase II (CAT II). Malonyl-CoA is an inhibitor of CAT I, which catalyzes the transfer of acyl groups from CoA to carnitine, thus allowing fatty acids to enter mitochondria for beta-oxidation. Therefore, Choice D is the correct answer.

Question 17

Medium-chain triacylglycerols may be an appropriate dietary supplement for an individual with a deficiency of

Accepted Answer

Medium-chain triacylglycerols can be directly absorbed into the bloodstream and transported to the liver without the need for carnitine, which is required for the transport of long-chain fatty acids into mitochondria for oxidation. Therefore, they are beneficial for individuals with carnitine deficiency.

Question 18

Which of the following statements about triacylglycerols is not true?

Accepted Answer

Triacylglycerols are primarily transported in the blood as components of lipoproteins, not bound to albumin. Albumin primarily binds free fatty acids in the bloodstream.

Question 19

Propionyl carboxylase is an enzyme required for the oxidation of

Accepted Answer

Propionyl carboxylase is required for the oxidation of fatty acids with an odd number of carbon atoms.

Question 20

A portion of the NADPH necessary for fatty acid biosynthesis is provided by:

Accepted Answer

Both the oxidative decarboxylation of malate by the malic enzyme and the pentose phosphate pathway provide NADPH necessary for fatty acid biosynthesis.

Quiz 17: Lipid Metabolism I: Synthesis, Storage, and Utilization of Fatty Acids and Triacylglycerols