Q.67 To which one of the following groups, the antibiotics kanamycin, streptomycin and gentamicin
belong
(A) cephalosporins (B) macrolides (C) aminoglycosides (D) quinolones
Kanamycin, streptomycin, and gentamicin are all aminoglycoside antibiotics that bind bacterial 30S ribosomal subunits to inhibit protein synthesis. They do not belong to cephalosporins, macrolides, or quinolones. The correct answer is (C) aminoglycosides.
Correct Answer
(C) Aminoglycosides
Antibiotic Class Characteristics
Aminoglycosides feature amino sugars linked to an aminocyclitol core (e.g., 2-deoxystreptamine in gentamicin/kanamycin; streptidine in streptomycin), targeting aerobic Gram-negatives like Pseudomonas via concentration-dependent killing and poor oral absorption (parenteral use). They cause nephro-/ototoxicity via ROS in kidney/cochlea.
Option Analysis
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(A) Cephalosporins: Wrong. Beta-lactams (e.g., cefotaxime) inhibit cell wall synthesis via PBPs; no ribosomal action.
-
(B) Macrolides: Wrong. Large lactone rings (e.g., erythromycin) block 50S peptidyl transferase; Gram-positive focus.
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(C) Aminoglycosides: Correct. Kanamycin/streptomycin/gentamicin prototypical; all 30S binders with similar spectra/toxicity.
-
(D) Quinolones: Wrong. DNA gyrase/topoisomerase IV inhibitors (e.g., ciprofloxacin); bactericidal, urinary/GI use.
Introduction to Kanamycin Streptomycin Gentamicin Classification
Kanamycin streptomycin gentamicin aminoglycosides classification is essential GATE Life Sciences microbiology, where Q.67 tests recognition of 30S ribosomal inhibitors vs other classes. Aminoglycosides uniquely target protein synthesis in Gram-negatives with shared toxicity profiles.
Aminoglycoside Core Features
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Structure: Aminosugars + aminocyclitol (streptomycin lacks 2-deoxystreptamine).
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MOA: 30S binding → mistranslation, membrane damage.
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Spectrum: Aerobic GNB (Pseudomonas for gentamicin); synergistic with beta-lactams.
Q.67 Class Comparison Table
| Class | Examples | Target | Key Difference |
|---|---|---|---|
| Cephalosporins | Cefotaxime | Cell wall | PBP inhibition |
| Macrolides | Erythromycin | 50S ribosome | Gram+ focus |
| Aminoglycosides | Kanamycin, streptomycin, gentamicin | 30S ribosome | Correct |
| Quinolones | Ciprofloxacin | DNA gyrase | No protein effect |
Why Aminoglycosides for GATE?
Kanamycin (kanR selection), streptomycin (TB), gentamicin (Pseudomonas) frequently tested together. High-yield: All nephrotoxic, once-daily dosing.
Exam Mastery Tips
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Mnemonic: “Amino-Gents Stream Kan” (gentamicin, streptomycin, kanamycin).
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Distinguish: Aminoglycosides (30S) vs macrolides (50S).
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PYQ pattern: Group drugs by shared core/structure.
Master kanamycin streptomycin gentamicin aminoglycosides for perfect pharmacology scores.
