Biology 9700 · AS & A Level · Natural and artificial selection

Natural and artificial selection — practice question

Penicillin-binding proteins (PBPs) are proteins located in the cell surface membrane of bacteria. PBPs catalyse the last stages in the formation of a peptidoglycan cell wall.
(a)[2]

Using the information above, describe the probable molecular structure of a PBP.

(b)[3]

Penicillin-resistant mutants of the bacterium, Staphylococcus aureus, make a PBP, PBP2a, that does not bind strongly to penicillin. Suggest how the presence of PBP2a in the cell surface membrane gives S. aureus resistance to the effects of penicillin.

(c)[2]

Explain why penicillin has no effect on viruses.

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