Antibiotics and antibiotic resistance

Overview

Recall questions on how different antibiotics attack a bacterium, why viruses are unaffected, the cell differences that make selective toxicity possible, how resistance spreads, and the hospital-acquired strains.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is an antibiotic?

   Model answer

   An antibiotic is a chemical, originally obtained from a microorganism, that kills bacteria or prevents them from growing.

2. 2

   Why do antibiotics have no effect on a viral infection?

   Model answer

   Viruses have no cell wall, no ribosomes of their own and no metabolism, so none of the structures an antibiotic targets are present; they use the host cell's machinery instead.

3. 3

   How does penicillin kill a bacterium?

   Model answer

   It inhibits the enzymes that cross-link the peptidoglycan of the cell wall, so a growing cell builds a weak wall, water enters by osmosis and the cell bursts.

4. 4

   Which structure do tetracycline and erythromycin act on, and with what effect?

   Model answer

   They bind to the bacterial 70S ribosome, blocking translation so the cell can no longer synthesise proteins.

5. 5

   Name an antibiotic that inhibits nucleic acid synthesis and state how it works.

   Model answer

   Ciprofloxacin inhibits DNA gyrase, the enzyme that unwinds bacterial DNA, so the DNA cannot be replicated.

6. 6

   State three differences between prokaryotic and eukaryotic cells that let an antibiotic harm bacteria without harming human cells.

   Model answer

   Bacteria have a peptidoglycan cell wall which human cells lack entirely, they have 70S ribosomes rather than the 80S ribosomes of human cytoplasm, and their DNA is circular and free in the cytoplasm rather than linear and enclosed in a nucleus.

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