All Free Biochemistry MCQs with Answers

• A. Acetone
• B. Acetocetate
• C. Acetic acid
• D. Beta hydroxybutyric acid

Explanation: The three ketone bodies are acetoacetate, beta-hydroxybutyrate and acetone.

• A. Blood
• B. Kidney
• C. Spleen
• D. Liver

Explanation: Ketone-body formation, or ketogenesis, occurs mainly in the mitochondria of liver cells during fasting or carbohydrate deficiency.

• A. Mitochondria
• B. Microsomes
• C. Cytoplasm
• D. All of the above

Explanation: The principal site of fatty-acid beta-oxidation is the mitochondrial matrix, where fatty acyl-CoA is repeatedly shortened to acetyl-CoA.

• A. Glutamate
• B. Acetoacetate
• C. Cholesterol
• D. Glycine

Explanation: When fatty acid oxidation is high, liver acetyl-CoA accumulates and is diverted into ketogenesis, producing acetoacetate.

• A. Double unpaired electron in an outer orbit
• B. Single paired electron in an outer orbit
• C. Single unpaired electron in an outer orbit
• D. Double paired electron in an outer orbit

Explanation: A free radical contains at least one unpaired electron, commonly in its outer orbital, making it highly reactive.

• A. Cyclic GMP
• B. Calcium ions
• C. Cyclic AMP
• D. Prostacyclins

Explanation: Nitric oxide activates soluble guanylyl cyclase, increasing cyclic GMP, which mediates effects such as vascular smooth-muscle relaxation.

• A. Hypoxia stimulates pyruvate dehydrogenase by increased, 2, 3DPG
• B. Hypoxia stimulates release of all glycolytic enzymes from Band 3 on RBC membrane
• C. Hypoxia inhibits hexokinase
• D. Activation of the regulatory enzymes by high PH

Explanation: During hypoxia, deoxyhaemoglobin binds the cytoplasmic domain of band 3 and displaces glycolytic enzymes, increasing their access to the…

• A. Catalase
• B. Acetaldehyde dehydrogenase
• C. Alcohol dehydrogenase
• D. Enolase

Explanation: Alcohol dehydrogenase oxidises ethanol to acetaldehyde, using NAD+ as the electron acceptor.

• A. Creatinine
• B. Phosphates
• C. Xanthine
• D. Uric acid

Explanation: In humans, purine bases are degraded through hypoxanthine and xanthine to uric acid, the principal end product excreted in urine.

• A. Urea
• B. Glutamine
• C. Creatinine
• D. Uric Acid

Explanation: Brain tissue detoxifies ammonia by combining it with glutamate to form glutamine through glutamine synthetase.

• A. 1 Kcal
• B. 41 Kcal
• C. 410 Kcal
• D. 4100 Kcal

Explanation: Protein yields approximately 4.1 kcal per gram when metabolised, so 10 g provides about 41 kcal.

• A. Tyrosine transaminase
• B. Cystathionase
• C. Pheylalanine hydroxylase
• D. Homogentisate oxidase

Explanation: Alkaptonuria results from deficiency of homogentisate oxidase in tyrosine degradation, causing homogentisic acid to accumulate and darken…

• A. Carbamyl synthetase
• B. Urease
• C. Arginase
• D. Ornithine

Explanation: Carbamoyl phosphate synthetase I catalyses the first, committed step of the urea cycle in liver mitochondria, forming carbamoyl phosphate…

• A. Uric acid
• B. Glutamine
• C. Urea
• D. Creatinine

Explanation: In the liver, toxic ammonia is converted into relatively harmless urea through the urea cycle, allowing its excretion by the kidneys.

• A. Glucose
• B. Fatty acid
• C. Glycerol
• D. Beta hydroxy butyrate

Explanation: After prolonged starvation, the brain adapts to use ketone bodies, especially beta-hydroxybutyrate, reducing its dependence on glucose.

• A. 6alactosemia
• B. Alkaptonuria
• C. Homocystinuria
• D. Phenyl ketonuria

Explanation: Phenylketonuria, alkaptonuria, and homocystinuria result from inherited defects in amino-acid metabolism.

• A. It is a tripetide
• B. It converts hemoglobin to methemoglobin
• C. It conjugates xenobiotics
• D. It scavenges free radicals and superoxide ions

Explanation: Glutathione is a tripeptide that detoxifies xenobiotics and protects cells by reducing reactive oxygen species.

• A. Brain
• B. Kidney
• C. Liver
• D. Intestine

Explanation: Urea is formed mainly in the liver through the urea cycle, which converts toxic ammonia into a less toxic compound for renal excretion.

• A. Urease
• B. Uricase
• C. Glutaminase
• D. Arginase

Explanation: Arginase catalyses the final urea-cycle reaction, splitting arginine into urea and ornithine.

• A. Fumarate
• B. Succinate
• C. Ornithine
• D. Aspartate

Explanation: Argininosuccinate is cleaved in the urea cycle to produce arginine and fumarate.