Biochemistry MCQs Set 2
26. Competitive inhibition increases:
A. Vmax
B. Km
C. Enzyme concentration
D. Product formation
Correct Answer: B. Km
Explanation: In competitive inhibition, the inhibitor competes with the substrate for the active site. This effectively lowers the affinity of the enzyme for its substrate, requiring more substrate to reach half-maximal velocity (Vmax), thus increasing the Km (Michaelis constant). The Vmax remains unchanged.
27. Diagnostic enzymes for liver damage include:
A. CK
B. LDH
C. ALT
D. Amylase
Correct Answer: C. ALT
Explanation: Alanine aminotransferase (ALT) is primarily found in the liver. When hepatocytes are damaged or die, ALT leaks into the bloodstream, making it a sensitive biomarker for liver injury in small animals.
28. Fat-soluble vitamins include:
A. B and C
B. A, D, E, K
C. B1,B2,B6
D. C and K
Correct Answer: B. A, D, E, K
Explanation: Vitamins A, D, E, and K are fat-soluble, meaning they are absorbed along with fats and can be stored in the liver and adipose tissue. This storage capacity increases the risk of toxicity compared to water-soluble vitamins (B and C).
29. Vitamin D deficiency causes:
A. Scurvy
B. Rickets
C. Night blindness
D. Pellagra
Correct Answer: B. Rickets
Explanation: Rickets is a disease in young animals caused by a deficiency in Vitamin D, calcium, or phosphorus, leading to soft, deformed bones. In adults, the same deficiency causes osteomalacia.
30. Vitamin K is essential for:
A. Vision
B. Bone formation
C. Blood clotting
D. Nerve function
Correct Answer: C. Blood clotting
Explanation: Vitamin K is a cofactor for the enzyme that activates clotting factors II, VII, IX, and X in the liver. A deficiency leads to prolonged clotting times and spontaneous hemorrhage.
31. Iron deficiency leads to:
A. Rickets
B. Anemia
C. Goiter
D. Tetany
Correct Answer: B. Anemia
Explanation: Iron is the central component of the heme group in hemoglobin. A deficiency results in iron-deficiency anemia, characterized by small, pale red blood cells (microcytic, hypochromic).
32. Calcium metabolism is regulated by:
A. Insulin
B. Thyroxine
C. Parathyroid hormone
D. Cortisol
Correct Answer: C. Parathyroid hormone (PTH)
Explanation: PTH increases blood calcium levels by stimulating bone resorption, increasing renal calcium reabsorption, and activating Vitamin D to increase intestinal absorption. Calcitonin works oppositely to lower blood calcium.
33. Hormones act through receptors located in:
A. Cell wall
B. Cytoplasm or membrane
C. Mitochondria only
D. Nucleus only
Correct Answer: B. Cytoplasm or membrane
Explanation: Water-soluble hormones (like insulin) bind to cell membrane receptors, while lipid-soluble hormones (like steroids) pass through the membrane to bind with receptors in the cytoplasm or nucleus.
34. Second messenger of adrenaline is:
A. ATP
B. cAMP
C. DNA
D. NADH
Correct Answer: B. cAMP
Explanation: Adrenaline binds to G-protein coupled receptors, activating adenylate cyclase, which converts ATP into cyclic AMP (cAMP). cAMP then triggers various intracellular responses.
35. Insulin lowers blood glucose by:
A. Glycogen breakdown
B. Increasing gluconeogenesis
C. Promoting glucose uptake
D. Increasing lipolysis
Correct Answer: C. Promoting glucose uptake
Explanation: Insulin stimulates the translocation of glucose transporters (GLUT4) to the cell membranes of muscle and adipose tissue, allowing glucose to enter cells and leave the bloodstream.
36. DNA is composed of:
A. Amino acids B. Fatty acids C. Nucleotides D. Sugars only
Correct Answer: C. Nucleotides
Explanation: The basic building blocks of DNA are nucleotides, each consisting of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases (A, T, C, G).
37. Complementary base pairing in DNA is:
A. A–C, G–T
B. A–T, G–C
C. A–G, C–T
D. U–A, G–C
Correct Answer: B. A–T, G–C
Explanation: In DNA, Adenine always pairs with Thymine via two hydrogen bonds, and Guanine pairs with Cytosine via three hydrogen bonds. This ensures the uniform width of the double helix.
38. RNA contains which base instead of thymine?
A. Cytosine B. Guanine C. Uracil D. Adenine
Correct Answer: C. Uracil
Explanation: RNA differs from DNA by having the base Uracil instead of Thymine. Uracil is complementary to Adenine.
39. Translation occurs on:
A. Ribosomes B. Mitochondria C. Golgi apparatus D. Lysosomes
Correct Answer: A. Ribosomes
Explanation: Translation is the process where the code carried by mRNA is read by ribosomes to synthesize a specific protein.
40. ATP is mainly generated by:
A. Glycolysis only B. TCA cycle only C. Oxidative phosphorylation D. Pentose pathway
Correct Answer: C. Oxidative phosphorylation
Explanation: While glycolysis and the TCA cycle produce some ATP, the vast majority of cellular ATP is generated via oxidative phosphorylation in the electron transport chain.
41. Electron transport chain (ETC) is located in:
A. Cytoplasm B. Outer mitochondrial membrane C. Inner mitochondrial membrane D. Nucleus
Correct Answer: C. Inner mitochondrial membrane
Explanation: The ETC is embedded in the cristae (inner membrane) of the mitochondria, where it uses a proton gradient to drive ATP synthesis.
42. Free radicals cause damage by:
A. Oxidation B. Reduction C. Hydrolysis D. Condensation
Correct Answer: A. Oxidation
Explanation: Free radicals are highly reactive molecules with unpaired electrons that “steal” electrons from lipids, proteins, and DNA through oxidation, leading to oxidative stress and cell damage.
43. Antioxidant enzyme is:
A. Amylase B. Catalase C. Pepsin D. Trypsin
Correct Answer: B. Catalase
Explanation: Catalase is a crucial antioxidant enzyme that breaks down harmful hydrogen peroxide (H2O2) into water and oxygen.
44. Liver function test includes:
A. Creatinine B. ALT C. Urea D. Uric acid
Correct Answer: B. ALT
Explanation: As mentioned in question 27, ALT is a classic marker used in a liver function profile. Urea and Creatinine are primarily markers of kidney function.
45. Elevated serum creatinine indicates:
A. Liver disease B. Muscle injury C. Kidney dysfunction D. Anemia
Correct Answer: C. Kidney dysfunction
Explanation: Creatinine is a waste product of muscle metabolism excreted by the kidneys. If the kidneys are not filtering properly, creatinine levels in the blood rise.
46. Normal blood glucose in animals is regulated by:
A. Thyroxine B. Insulin and glucagon C. Cortisol only D. Aldosterone
Correct Answer: B. Insulin and glucagon
Explanation: Insulin lowers blood sugar after eating, while glucagon raises it during fasting by stimulating glycogen breakdown in the liver.
47. Rumen microbes convert carbohydrates into:
A. Glucose B. Lactose C. Volatile fatty acids (VFAs) D. Glycogen
Correct Answer: C. Volatile fatty acids (VFAs)
Explanation: In the rumen, microbial fermentation breaks down cellulose and starch into VFAs (primarily acetate, propionate, and butyrate), which are then absorbed through the rumen wall.
48. Major energy source for ruminants is:
A. Glucose B. Acetate C. Glycogen D. Lactate
Correct Answer: B. Acetate
Explanation: Unlike monogastric animals that rely on glucose, ruminants get up to 70% of their energy from VFAs. Acetate is the primary VFA circulating in the blood and used for energy and milk fat synthesis.
49. Microbial protein is digested in:
A. Rumen B. Reticulum C. Abomasum D. Omasum
Correct Answer: C. Abomasum
Explanation: Microbes that pass out of the rumen are killed and digested by acids and enzymes in the abomasum (the “true stomach”), providing the host with high-quality protein.
50. Phase I detoxification mainly involves:
A. Reduction and oxidation B. Conjugation C. Methylation D. Sulfation
Correct Answer: A. Reduction and oxidation
Explanation: The liver detoxifies substances in two phases. Phase I involves oxidation, reduction, or hydrolysis (often mediated by Cytochrome P450) to make the molecule more polar. Phase II involves conjugation.