RDN Nutritional Biochemistry 2

Question 1

Which enzyme is responsible for the rate-limiting step in fatty acid synthesis?

Accepted Answer

Acetyl-CoA carboxylase

Answer

Acetyl-CoA carboxylase catalyzes the conversion of acetyl-CoA to malonyl-CoA, which is the committed, rate-limiting step in de novo fatty acid synthesis.

Question 2

During prolonged fasting, the liver produces ketone bodies primarily from which substrate?

Accepted Answer

Acetyl-CoA from fatty acid beta-oxidation

Answer

During fasting, elevated fatty acid beta-oxidation generates excess acetyl-CoA that exceeds the TCA cycle capacity, leading to ketone body synthesis (ketogenesis) in liver mitochondria.

Question 3

Which B vitamin serves as a cofactor for transaminase (aminotransferase) enzymes involved in amino acid metabolism?

Accepted Answer

Pyridoxine (B6)

Answer

Pyridoxal phosphate (PLP), the active form of vitamin B6, is an essential cofactor for all transaminase reactions that transfer amino groups between amino acids and alpha-keto acids.

Question 4

What is the primary function of the pentose phosphate pathway in erythrocytes?

Accepted Answer

Generation of NADPH to maintain glutathione in reduced form

Answer

In red blood cells, the pentose phosphate pathway generates NADPH needed to keep glutathione reduced, protecting cells from oxidative damage caused by reactive oxygen species.

Question 5

Homocysteine accumulation in the blood is associated with deficiencies in which combination of nutrients?

Accepted Answer

Folate, vitamin B6, and vitamin B12

Answer

Folate, B6 (as PLP), and B12 are all required in the methionine cycle; deficiency of any one leads to impaired homocysteine remethylation or transsulfuration, causing hyperhomocysteinemia.

(RDN) Registered Dietitian Nutritionist Practice Test

(RDN) Registered Dietitian Nutritionist Practice Test

RDN Nutritional Biochemistry 2