Biochemistry End-of-Year 2020 — Past Paper OmpathStudy

Biochemistry EOY 2020 — Complete Question Paper All 100 questions transcribed from the source paper. The original had no printed answer key — every answer and explanation below has been composed from standard biochemistry and general-chemistry teaching to fill that gap (never left blank or guessed silently). Question 1 1.0 The synthesis of Thymidine Monosphosphate (TMP) requires all BUT one; A. Folic acid B. Fluorouracil C. NADPH D. Thymidylate synthase E. dihydrofolate reductase ✅ Answer: B. Fluorouracil Explanation: 5-Fluorouracil is a chemotherapy drug that INHIBITS thymidylate synthase; it is not a requirement for TMP synthesis. Folate, NADPH, thymidylate synthase and dihydrofolate reductase are all genuinely needed to convert dUMP to dTMP. --- Question 2 Which of the following statements is TRUE about Molisch’s test for carbohydrates? A. It is negative for non-reducing sugars B. It is negative for aldo sugars C. It is positive for all carbohydrates D. It is negative for reducing sugars E. It is negative for pentoses ✅ Answer: C. It is positive for all carbohydrates Explanation: Molisch's test (α-naphthol + concentrated H2SO4, forming a purple ring) is a general test positive for essentially all carbohydrates, since it depends on acid-catalysed dehydration to furfural/hydroxymethylfurfural. --- Question 3 Question text In reference to Lewis structures of PCl3 and SCl4; A. Dative bond exists in the latter but not in the former B. Both have a dative bond C. Both have a lone pair of electrons D. Dative bond exists in the former but not in the latter E. Each has three bonding pairs of electrons ✅ Answer: C. Both have a lone pair of electrons Explanation: Both PCl3 and SCl4 have exactly one lone pair on the central atom (P and S respectively), which is the one universally true structural fact among the options. --- Question 4 Question text The following are components of Coenzyme A, EXCEPT A. Ribose B. β-mercaptoethylamine C. Pantothenic acid D. 3’-phosphoadenosine diphosphate (3’-PADP) E. glutamate ✅ Answer: E. glutamate Explanation: Coenzyme A is built from pantothenic acid + β-mercaptoethylamine (pantetheine) linked to 3′-phosphoadenosine diphosphate (ADP with a 3′-phosphate) and its ribose. Glutamate is not part of its structure. --- Question 5 Question text Macromolecules’ three-dimensional structure is formed and maintained by the following noncovalent interactions, except. A. Hydrogen bonds B. Hydrophobic interactions C. Carbon-carbon bonds D. Ionic interactions E. Van der Waals interactions ✅ Answer: C. Carbon-carbon bonds Explanation: Carbon-carbon bonds are covalent, not noncovalent — 3D macromolecular structure is instead held together by hydrogen bonds, hydrophobic effects, ionic interactions and van der Waals forces. --- Question 6 Question text Saliva has a [H3O+] of 10-8 while compound B has pOH of 6. Which one is more acidic? A. Saliva, pH 8 B. Compound B, pH 8 C. Both have equal acidity, pH 8 D. Compound B, pH 6 E. Saliva, pH 6 ✅ Answer: C. Both have equal acidity, pH 8 Explanation: [H3O+]=10⁻⁸ M gives pH 8. pOH 6 gives pH = 14 − 6 = 8. Identical pH means identical acidity. --- Question 7 Question text A prosthetic group of a protein is a non-protein structure that is: A. Permanently associated with the protein. B. A part of the secondary structure of the protein. C. A substrate of the protein. D. Transiently bound to the protein E. A ligand of the protein. ✅ Answer: A. Permanently associated with the protein. Explanation: A prosthetic group is a non-protein component permanently/tightly bound to a protein (e.g. heme in hemoglobin), as opposed to a substrate or transiently-bound ligand. --- Question 8 Question text A solution with pH = 5 is than a solution with pH = 7. A. 200 times more basic B. 10 times more basic C. 10 times more acidic D. 100 times more acidic E. 2 times more basic ✅ Answer: D. 100 times more acidic Explanation: Each pH unit is a 10-fold difference in [H+]; pH 5 vs pH 7 is a 2-unit difference, i.e. 10² = 100 times more acidic. --- Question 9 Inadequate tryptophan in the diet can lead to low levels of; A. Pyridoxine B. Vitamin C C. Pantothenic acid D. Niacin E. Vitamin A ✅ Answer: D. Niacin Explanation: Tryptophan is a precursor for endogenous niacin (vitamin B3) synthesis, so dietary tryptophan deficiency can precipitate niacin deficiency (pellagra). --- Question 10 Glucokinase is to be found in the liver and in the pancreatic β-cells. Which of the following is NOT true about glucokinase? A. It is induced by insulin B. It is not inhibited by G-6-P C. Its affinity for glucose is higher than that of hexokinase D. Its Vmax value is higher than that of hexokinase E. Its Km is for glucose is higher than that of hexokinase ✅ Answer: C. Its affinity for glucose is higher than that of hexokinase Explanation: This is the false statement, which is what the question asks for: glucokinase actually has LOWER affinity for glucose (higher Km) than hexokinase, not higher. It is correctly