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CSRI JRF NET Life Sciences June 2017 Model Question Paper Set- 4

biological significance of hydrogen bonds in water

CSIR JRF/NET Life Science Exam June 2017 (I)
Model Question Paper 4/5
(CSIR MCQ011: Practice Questions with Answer Key)

1.  Penicillin-resistant bacteria produce β-lactamase which inactivates penicillin by:

a.       Esterifying the carboxyl group
b.      Oxidizing S atom
c.       Hydrolyzing the side chain
d.      Hydrolyzing the C-N bond

Ans. (d)

β-lactamases or penicillinase are a class of enzymes produced by some bacteria which degrade penicillin antibiotic and thereby impart resistance against penicillin. All penicillin antibiotics contain a β-lactum ring structure which is essential for the antibiotic activity. The β-lactamase enzyme will degrade the β-lactum ring and thus inhibit the antibiotic properties.

2. Pseudo-murein is present in cell wall of:

a.       Streptococci
b.      Staphylococci
c.       Methanococci
d.      Micrococci

Ans. (c). Methanococci

Methanococci is an Archaebacteria.

Pseudo-murein or pseudo-peptidoglycan is a major cell wall component of some Archaebacteria. It is structurally different from the peptidoglycan of the true bacteria. However, it is functionally similar to the peptidoglycan wall of bacteria. Pseudo-murein is a hetero-polysaccharide of N-acetylglucosamine and N-acetyltalosaminuronic acid connected by β-1,3-glycosidic bonds. Lysozyme enzyme is unable to degrade the pseudo-murein cell wall.

Learn more: Comparison table of Bacteria, Archaea and Eukarya

3. Bacteria that can penetrate intact corneal epithelium is:

a.      Pseudomonas aeruginosa
b.      Staphylococus aureus
c.       Listeria monocytogenes
d.      Yersinia pestis

Ans. (b). Staphylococus aureus

4. Which of the following bacterial toxins does not have ADP-ribosyl transferase activity:

a.       Cholera toxin
b.      Diphtheria toxin
c.       Exotoxin A
d.      S aureus α toxin

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