User interface language: English | Español

Date November 2018 Marks available 2 Reference code 18N.3.sl.TZ0.12
Level SL Paper 3 Time zone TZ0
Command term Explain Question number 12 Adapted from N/A

Question

The structure of penicillin is shown in section 37 of the data booklet.

State the internal bond angles in the β-lactam ring and the expected bond angles for the same atoms in an open structure.

[2]
a.

Explain how the open β-lactam ring kills bacteria.

[2]
b.

Outline one effect of over-prescription of penicillin.

[1]
c.

State how the structure of penicillin can be changed to combat this effect.

[1]
d.

Suggest why human cells are not affected by penicillin.

[1]
e.

Markscheme

Accept “109º”.

a.

«irreversibly» binds/bonds to enzyme/transpeptidase

OR

inhibits enzyme/transpeptidase «in bacteria» that produces cell walls

OR

prevents cross-linking of bacterial cell walls ✔

 

cells absorb water AND burst

OR

cells cannot reproduce ✔

 

Accept “reacts with” for “bonds to” for M1.

Do not accept “cell membrane” for “cell wall” for M1.

Accept “cells burst due to osmotic pressure” for M2.

Accept “bacteria” for “cells” for M2.

b.

Any one of:

leads to «bacterial» resistance «to antibiotics»

OR

makes antibiotics less effective

OR

increased side effects due to larger dosages/over time ✔

 

increases proportion of resistant bacteria ✔

 

destroys useful/beneficial bacteria

OR

destroyed bacteria replaced by more harmful bacteria ✔

 

resistant bacteria pass on their mutation to next generation ✔

damage to ecosystems ✔

 

Accept “superbugs such as MRSA develop” but superbug must be identified.

Accept “immune” for resistant but do not accept “tolerance”

c.

«modify» side-chain ✔

 

Accept “«modify» R”.

d.

no cell walls

OR

humans do not have transpeptidase ✔

e.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.
[N/A]
d.
[N/A]
e.

Syllabus sections

Options » D: Medicinal chemistry » D.2 Aspirin and penicillin
Show 65 related questions
Options » D: Medicinal chemistry
Options

View options