RDN Nutritional Biochemistry 3 — Questions and Answers
Question 1: Which lipoprotein is primarily responsible for transporting dietary fat from the intestine to peripheral tissues?
- VLDL
- LDL
- Chylomicrons (Correct answer)
- HDL
Correct answer: Chylomicrons
Chylomicrons are assembled in intestinal enterocytes and transport dietary triglycerides, cholesterol, and fat-soluble vitamins via the lymphatic system to peripheral tissues.
Question 2: Pyruvate dehydrogenase complex requires five cofactors; which of the following is NOT one of them?
- Thiamin pyrophosphate (TPP)
- Lipoic acid
- FAD
- Pyridoxal phosphate (PLP) (Correct answer)
Correct answer: Pyridoxal phosphate (PLP)
The pyruvate dehydrogenase complex uses TPP, lipoic acid, FAD, NAD+, and CoA (derived from pantothenic acid) as cofactors, but does NOT require pyridoxal phosphate (PLP/B6).
Question 3: In the context of iron absorption, what effect does ascorbic acid (vitamin C) have?
- Converts ferric (Fe3+) to ferrous (Fe2+) form, enhancing absorption (Correct answer)
- Converts ferrous (Fe2+) to ferric (Fe3+) form, enhancing absorption
- Binds iron to form an insoluble complex, reducing absorption
- Increases hepcidin production to regulate iron storage
Correct answer: Converts ferric (Fe3+) to ferrous (Fe2+) form, enhancing absorption
Vitamin C reduces dietary non-heme iron from the ferric (Fe3+) to the more soluble ferrous (Fe2+) form, which is the form transported by DMT-1 across the intestinal epithelium.
Question 4: Which enzyme converts arachidonic acid into prostaglandins and thromboxanes?
- Lipoxygenase
- Cyclooxygenase (COX) (Correct answer)
- Phospholipase A2
- Delta-6-desaturase
Correct answer: Cyclooxygenase (COX)
Cyclooxygenase (prostaglandin H synthase) catalyzes the conversion of arachidonic acid into prostaglandin H2, the precursor for all prostaglandins and thromboxanes via the COX pathway.
Question 5: What is the net ATP yield from complete oxidation of one molecule of glucose via glycolysis, TCA cycle, and oxidative phosphorylation?
- 8 ATP
- 15 ATP
- 30-32 ATP (Correct answer)
- 38 ATP
Correct answer: 30-32 ATP
Using current P/O ratios (2.5 for NADH, 1.5 for FADH2), complete glucose oxidation yields approximately 30-32 ATP, lower than the older textbook value of 36-38.
Question 6: Which metabolic condition leads to increased production of VLDL by the liver?
- Prolonged fasting with low insulin
- Hyperglycemia and hyperinsulinemia in metabolic syndrome (Correct answer)
- Severe protein deficiency (kwashiorkor)
- High dietary fiber intake
Correct answer: Hyperglycemia and hyperinsulinemia in metabolic syndrome
Chronic hyperglycemia and elevated insulin in metabolic syndrome stimulate hepatic de novo lipogenesis and VLDL assembly, leading to hypertriglyceridemia and increased cardiovascular risk.
Question 7: Zinc is a required cofactor for which important antioxidant enzyme?
- Glutathione peroxidase
- Catalase
- Cu/Zn superoxide dismutase (Correct answer)
- Thioredoxin reductase
Correct answer: Cu/Zn superoxide dismutase
Cytosolic Cu/Zn superoxide dismutase requires both copper and zinc to dismutate superoxide radicals (O2•−) into hydrogen peroxide and oxygen, providing a key antioxidant defense.
RDN Nutritional Biochemistry 3
Which lipoprotein is primarily responsible for transporting dietary fat from the intestine to peripheral tissues?