Biochemistry MCQs Set 4
76. Oxidative phosphorylation is uncoupled by:
A. ATP
B. Cyanide
C. 2,4-dinitrophenol
D. Oxygen
Correct Answer: C. 2,4-dinitrophenol Explanation: Uncouplers like 2,4-dinitrophenol (DNP) collapse the proton gradient across the inner mitochondrial membrane. This allows electron transport to continue without the production of ATP, dissipating energy as heat instead. Cyanide is an inhibitor, not an uncoupler, as it stops the electron transport chain entirely.
77. Major site of detoxification in the body is:
A. Kidney
B. Lung
C. Liver
D. Spleen
Correct Answer: C. Liver Explanation: The liver is the primary metabolic hub for processing toxins, drugs, and metabolic waste (like ammonia). It utilizes specialized enzyme systems to convert fat-soluble toxins into water-soluble substances for excretion.
78. Cytochrome P450 enzymes are involved in:
A. Protein synthesis
B. Phase I detoxification
C. Glycolysis
D. Urea formation
Correct Answer: B. Phase I detoxification Explanation: Cytochrome P450 enzymes are heme-containing proteins that catalyze oxidation reactions. They are the most critical enzymes in Phase I metabolism, making lipophilic compounds more polar to prepare them for Phase II conjugation.
79. Elevated ALT and AST indicate damage to:
A. Kidney
B. Heart
C. Liver
D. Brain
Correct Answer: C. Liver Explanation: Both ALT (Alanine Aminotransferase) and AST (Aspartate Aminotransferase) are leakage enzymes. While AST is also found in muscle, elevated levels of both—particularly ALT in dogs and cats—are classic indicators of hepatocellular necrosis or damage.
80. Which parameter is used to assess kidney function?
A. ALT
B. Urea
C. Bilirubin
D. Albumin
Correct Answer: B. Urea Explanation: Blood Urea Nitrogen (BUN) and Creatinine are the primary biomarkers for renal health. Because the kidneys are responsible for excreting urea, a rise in blood levels (azotemia) suggests a decrease in the glomerular filtration rate.
81. Hypocalcemia in dairy cows is commonly known as:
A. Ketosis
B. Milk fever
C. Bloat
D. Acidosis
Correct Answer: B. Milk fever Explanation: Milk fever (Parturient Paresis) occurs around calving when the sudden demand for calcium in milk exceeds the cow’s ability to mobilize calcium from her bones, resulting in muscle weakness and recumbency.
82. The major volatile fatty acid responsible for milk fat synthesis is:
A. Propionate
B. Butyrate
C. Acetate
D. Lactate
Correct Answer: C. Acetate Explanation: Acetate is the primary Volatile Fatty Acid (VFA) produced during the fermentation of roughage. It is the major precursor for de novo fatty acid synthesis in the mammary gland, directly impacting milk fat percentage.
83. Propionate in ruminants is primarily used for:
A. Fat synthesis
B. Protein synthesis
C. Glucose synthesis
D. Ketone formation
Correct Answer: C. Glucose synthesis Explanation: Propionate is the only glucogenic VFA. It is transported to the liver and serves as the major substrate for gluconeogenesis, providing the ruminant with nearly all of its blood glucose.
84. Which compound acts as an antioxidant vitamin?
A. Vitamin B₁
B. Vitamin C
C. Vitamin K
D. Vitamin D
Correct Answer: B. Vitamin C Explanation: Vitamin C (Ascorbic acid) and Vitamin E are potent antioxidants. They neutralize free radicals and reactive oxygen species, protecting cellular membranes and DNA from oxidative damage.
85. Albumin is synthesized in the:
A. Kidney
B. Spleen
C. Liver
D. Bone marrow
Correct Answer: C. Liver Explanation: Albumin is the most abundant plasma protein and is exclusively synthesized by the liver. Decreased serum albumin (hypoalbuminemia) often indicates chronic liver disease or protein-losing nephropathy/enteropathy.
86. Deamination of amino acids mainly occurs in:
A. Muscle
B. Brain
C. Liver
D. Kidney
Correct Answer: C. Liver Explanation: Oxidative deamination (the removal of the amino group from an amino acid) primarily occurs in the liver via the enzyme glutamate dehydrogenase, releasing ammonia for the urea cycle.
87. Which amino acid transports ammonia from muscle to liver?
A. Glutamate
B. Alanine
C. Glycine
D. Serine
Correct Answer: B. Alanine Explanation: In the Glucose-Alanine Cycle, muscle tissue exports nitrogen in the form of Alanine. Once it reaches the liver, it is converted back to pyruvate (for glucose synthesis) and ammonia (for urea synthesis).
88. Rate-limiting enzyme of cholesterol synthesis is:
A. Acetyl-CoA carboxylase
B. HMG-CoA reductase
C. Lipoprotein lipase
D. Cholesterol esterase
Correct Answer: B. HMG-CoA reductase Explanation: HMG-CoA reductase is the primary regulatory point for cholesterol production. Statin drugs work by inhibiting this specific enzyme.
89. LDL mainly transports:
A. Triglycerides
B. Cholesterol to tissues
C. Fat-soluble vitamins
D. Free fatty acids
Correct Answer: B. Cholesterol to tissues Explanation: Low-Density Lipoprotein (LDL) is often termed “bad cholesterol” because its role is to deliver cholesterol from the liver to peripheral tissues. Excessive levels can lead to lipid accumulation in vessels.
90. The biological value of a protein depends on:
A. Fat content
B. Amino acid composition
C. Digestibility only
D. Energy content
Correct Answer: B. Amino acid composition Explanation: Biological Value (BV) measures how efficiently the body can utilize a protein. This is determined by the completeness of its essential amino acid profile and how closely it matches the animal’s requirements.
91. Which hormone promotes lipolysis?
A. Insulin
B. Glucagon
C. Aldosterone
D. Thyroxine
Correct Answer: B. Glucagon Explanation: Glucagon (and adrenaline) stimulates hormone-sensitive lipase in adipose tissue to break down triglycerides into free fatty acids and glycerol for energy during fasting. Insulin inhibits this process.
92. Metabolic acidosis is characterized by:
A. Increased blood pH
B. Decreased blood pH
C. Increased bicarbonate
D. Decreased CO₂
Correct Answer: B. Decreased blood pH Explanation: Metabolic acidosis occurs when there is an accumulation of acids or a loss of bicarbonate, resulting in a drop in blood pH below the normal range (usually <7.35).
93. Which enzyme protects cells from hydrogen peroxide?
A. Superoxide dismutase
B. Catalase
C. Peroxidase
D. Oxidase
Correct Answer: B. Catalase Explanation: Catalase is a high-turnover enzyme that rapidly converts hydrogen peroxide (H2O2) into harmless water and oxygen, preventing the formation of more toxic hydroxyl radicals.
94. Which biochemical test estimates protein concentration?
A. Benedict’s test
B. Biuret test
C. Barfoed’s test
D. Molisch test
Correct Answer: B. Biuret test Explanation: The Biuret test uses copper ions in an alkaline solution to react with peptide bonds, producing a purple color. The intensity of the color is directly proportional to the protein concentration.
95. Creatine kinase (CK) is elevated in diseases of:
A. Liver
B. Kidney
C. Muscle
D. Pancreas
Correct Answer: C. Muscle Explanation: Creatine Kinase is an enzyme found in high concentrations in cardiac and skeletal muscle. It is the most specific indicator of muscle injury, inflammation, or physical trauma in veterinary diagnostics.
96. Which hormone increases blood calcium level?
A. Calcitonin
B. Parathyroid hormone
C. Insulin
D. Cortisol
Correct Answer: B. Parathyroid hormone (PTH) Explanation: As noted previously, PTH raises blood calcium by mobilizing it from bone and reducing its excretion. Calcitonin is its antagonist, helping to lower blood calcium.
97. Glucose absorption in intestine occurs mainly by:
A. Passive diffusion
B. Facilitated diffusion
C. Active transport
D. Endocytosis
Correct Answer: C. Active transport Explanation: Glucose is absorbed against its concentration gradient via Secondary Active Transport, using the SGLT1 (Sodium-Glucose Linked Transporter) protein, which couples glucose movement with sodium.
98. Which compound is a high-energy phosphate molecule?
A. AMP
B. ADP
C. ATP
D. cAMP
Correct Answer: C. ATP Explanation: Adenosine Triphosphate (ATP) is the universal energy currency of the cell. The energy is stored in the high-energy phosphoanhydride bonds between the phosphate groups.
99. Which condition results from prolonged protein deficiency?
A. Kwashiorkor
B. Rickets
C. Scurvy
D. Pellagra
Correct Answer: A. Kwashiorkor Explanation: Kwashiorkor is a condition of severe protein-energy malnutrition characterized by edema (swelling) and an enlarged liver, distinct from Marasmus, which is a general calorie deficiency.
100. The primary role of biochemistry in veterinary medicine is to:
A. Study microbes
B. Understand metabolic basis of disease
C. Diagnose parasites
D. Formulate vaccines
Correct Answer: B. Understand metabolic basis of disease Explanation: Biochemistry provides the foundation for understanding how health and disease are reflected at the molecular and metabolic level, enabling the diagnosis and treatment of conditions like diabetes, ketosis, and organ failure.