| Date | November 2016 | Marks available | 1 | Reference code | 16N.3.HL.TZ0.9 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Predict | Question number | 9 | Adapted from | N/A |
Question
Lipid A is a phospholipid that makes up the external layer of the outer membranes of most Gram-negative bacteria. LpxC is an enzyme involved in the biosynthesis of lipid A. In this experiment, a lawn of the Gram-negative bacterium Escherichia coli was grown on a nutrient agar plate. Shortly after inoculation, before the lawn is formed, discs containing different test compounds were placed on top. The Petri dish shows the results after 24 hours incubation.
Outline the effect of disc 3 on the bacterial lawn.
Outline the effect of mutating the LpxC inhibitor.
Predict the results obtained with disc 1 in a Gram-positive bacterial lawn.
Markscheme
a. the antibiotic/ampicillin diffuses out
b. killing bacteria/inhibiting growth of bacteria
c. zone of inhibition/clearing formed
lipid A production/synthesis is not inhibited so bacteria can grow
OR
bacteria grow/are not affected since inhibitor function is lost
no inhibition of growth, since Gram-positive do not have lipid A in membrane/OWTTE
