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
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:
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.
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