1. Which of the following is the rate limiting enzyme in glycolytic pathway?

A. Glucose 6 phosphate
B. pyruvate carboxylase
C. Phosphoglucomutase
D. Phosphofructokinase

Answer- Option D

Phosphofructokinase is the enzyme involved in the rate limiting step of glycolysis, in which fructose 6 phosphate is converted to fructose 1,6 bisphosphate.

2. Which of the following is not true about competitive inhibition of enzymes

A. The inhibitor is structural analogue of the substrate
B. Reversible
C. Vmax is decreased
D. Km is increased

Answer: C (Vmax is decreased)

Competitive inhibition

• Drug structurally similar to the substrate
• Competes with the substrate for catalytic binding site of the enzyme
• Reversible
• Increase the rate constant Km and Vmax is unchanged. ie higher concentration of the substrate is required to achieve ½ maximal reaction velocity . If substrate concentration is increased, it can displace the drug and same maximum reaction velocity can be attained.

Example: Physostigmine and Neostigmine compete with Acetyl choline for cholinesterase.

3. Immunoglobulin that mediates primary immune response

A. IgA
B. IgE
C. IgM
D. IgD

Answer: C

The IgM (M stands for macroglobulin) class is the largest antibody molecule and, in serum, consists of a pentamer (five monomers) whose tail segments are connected by a glycoprotein. It is the first, albeit short-lived, immunoglobulin to appear in the circulation after antigenic stimulation.

PROVIDES PRIMARY ANTIBODY RESPONSE

4. All the following are products formed from tyrosine except

A. Melanin
B. Serotonin
C. Epinephrine
D. Dopamine

Answer- B

Serotonin is derived from tryptophan. Derivatives of tyrosine are dopamine, norepinephrine,
epinephrine, thyroid hormones and melanin.

5. Which of the following lipoprotein transport cholesterol from liver to peripheral
tissues?

A. Chylomicron
B. very low density lipoprotein
C. Low density lipoprotein
D. high density lipoprotein

Answer- C

Lipoproteins:-

• HDL- Transport cholesterol from tissues to liver
• LDL- transport cholesterol from liver to tissues; highest concentration of cholesterol, role in Coronary heart disease.
• Chylomicrons- transport exogenous triacylglycerol to various tissues, highest percentage of triacylglycerol
• VLDL- transport endogenous triacylglycerol to various tissues

6. Mechanism of action of diphtheria toxin is by

A. Increasing adenylate cyclase activity
B. Blocking the production and release of acetylcholine at NMJ
C. Inactivating elongation factor EF-2
D. Causing lysis of erythrocytes

Answer- C

Diphtheria toxin inactivates the elongation factor (EF 2) needed for protein synthesis. Specifically it transfers the ADP ribose moiety of NAD to EF 2 and inactivates EF 2 resulting in inhibition of cellular protein synthesis and ultimately cell death by apoptosis.

7. Vincent’s angina is caused by

A. Staphylococcus aureus
B. Leptotrichia buccalis
C. Streptococcus viridans
D. Haemophilus Influenza

Answer- B

Vincent’s angina also known as acute necrotizing ulcerative gingivitis, trench mouth or Vincent stomatitis, is an acute and painful infection of the tooth margins and gums .

8. Selective media for isolation of mycobacterium tuberculosis is

A. Loefflers serum slope
B. Lowenstein-Jensen medium
C. Thayer martin medium
D. Wilson blair medium

Answer: B

This medium is used for primary isolation of mycobacterium species.

9. The antibody responsible for anaphylactic reaction is

A. IgG
B. IgA
C. IgD
D. IgE

Answer: D

Anaphylaxis is an acute, life-threatening hypersensitivity disorder defined as a generalized, rapidly evolving, multi-systemic allergic reaction. Anaphylactic reactions were classified as IgE-mediated responses, that involves the release of numerous chemical mediators from the degranulation of basophils and mast cells after re-exposure to a specific antigen.

10. Germ tube formation is shown by

A. Candida kefyr
B. Candida tropicalis
C. Candida parapsilosis
D. Candida albicans

Answer- D

Candida albicans exhibit Reynold’s Braude phenomenon- Formation of germ tubes within 2hrs when incubated in human serum at 370C.