Fatty Acid Metabolism

Which of the following is not a role of lipids in microbial cells?

• component of membranes

• carrier in LPS and peptidoglycan synthesis

• alternative forms of energy

• protective coat of many organisms

• none of the above

Answer explanation

All listed roles are indeed functions of lipids in microbial cells. They are components of membranes, carriers in LPS and peptidoglycan synthesis, alternative energy sources, and protective coats. Thus, 'none of the above' is correct.

Which of the following is not a product of lipid catabolism?

• amino acids

• fatty acids

• glycerol

• ketone bodies

• all the above

Answer explanation

Amino acids are products of protein catabolism, not lipid catabolism. Lipid catabolism primarily produces fatty acids, glycerol, and ketone bodies.

Which of the following is not true about beta-oxidation of fatty acids?

• It involves the sequential removal of two-carbon units

• It generates acetyl-CoA as a primary product

• It directly produces glucose as an end product

• All the above

• It occurs in the cytoplasm of a bacterial cell

Answer explanation

Beta-oxidation does not produce glucose; it primarily generates acetyl-CoA. The process involves removing two-carbon units and occurs in the mitochondria of eukaryotes, not the cytoplasm of bacteria.

True or False. In beta-oxidation, activation of fatty acid to give a fatty acyl adenylate is necessary.

• True

• False

Answer explanation

True. In beta-oxidation, the activation of fatty acids to form fatty acyl adenylate is essential for their subsequent breakdown into acetyl-CoA units.

Which of the following is true about the oxidation of odd-numbered fatty acids?

• It exclusively occurs in the cytoplasm of cells

• It requires the addition of oxygen molecules in every step

• all the above

• It results in the production of only acetyl-CoA molecules

• It produces propionyl-CoA as one of its final products

Answer explanation

The oxidation of odd-numbered fatty acids produces propionyl-CoA as a final product, unlike even-numbered fatty acids which only yield acetyl-CoA. Thus, the correct statement is that it produces propionyl-CoA.

Which of the following is true about the oxidation of odd-numbered fatty acids via the methylcitrate pathway in microorganisms?

• The pathway produces succinate as an intermediate, allowing entry into the citric acid cycle.

• The methylcitrate pathway only occurs in the presence of high oxygen levels.

• It converts propionyl-CoA directly into acetyl-CoA without any intermediate steps.

• all the above

• Methylcitrate synthase is a key enzyme that initiates the conversion of propionyl-CoA in this pathway.

Answer explanation

Methylcitrate synthase is crucial in the methylcitrate pathway, initiating the conversion of propionyl-CoA. The other statements are incorrect regarding the pathway's intermediates and conditions.

Which of the following is true about the oxidation of unsaturated fatty acids by microorganisms?

• all the above

• Microorganisms can only oxidize saturated fatty acids and cannot process unsaturated ones.

• Double bonds in unsaturated fatty acids are removed before oxidation begins.

• Unsaturated fatty acids are oxidized in the same manner as saturated fatty acids without any modifications.

• Unsaturated fatty acids require additional enzymes like enoyl-CoA isomerase for complete oxidation.

Answer explanation

Unsaturated fatty acids require additional enzymes like enoyl-CoA isomerase for complete oxidation, as their double bonds necessitate specific modifications during the oxidation process.

Which of the following enzymes is commonly involved in the oxidation of unsaturated fatty acids by microorganisms?

• Citrate synthase

• Enoyl-CoA isomerase

• Succinyl-CoA synthetase

• Acetyl-CoA carboxylase

Answer explanation

Enoyl-CoA isomerase is crucial for the oxidation of unsaturated fatty acids, as it converts cis double bonds to trans, allowing for further degradation. The other enzymes listed are not directly involved in this specific process.

Why do microorganisms need additional enzymes to oxidize unsaturated fatty acids?

• Unsaturated fatty acids have double bonds that must be rearranged for complete oxidation.

• Unsaturated fatty acids are too large to enter the cell without modification.

• Unsaturated fatty acids cannot release energy through oxidation.

• Double bonds are converted into saturated bonds before beta-oxidation can occur.

Answer explanation

The presence of double bonds in unsaturated fatty acids requires microorganisms to use specific enzymes, like enoyl-CoA isomerase and 2,4-dienoyl-CoA reductase, to modify and align the bonds for successful beta-oxidation.

How many rounds of beta-oxidation are needed to completely oxidize a fatty acid with 16 carbon atoms?

• 4 rounds

• 5 rounds

• 7 rounds

• 8 rounds

Answer explanation

For a fatty acid with an even number of carbon atoms (like 16), beta-oxidation removes two-carbon units per round. Therefore, 7 rounds of beta-oxidation are needed to completely oxidize a 16-carbon fatty acid. The 7th and final round will release two (2) two-carbon units.