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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	Outline	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.

[2]

a.

Outline the effect of mutating the LpxC inhibitor.

[1]

b.

Predict the results obtained with disc 1 in a Gram-positive bacterial lawn.

[1]

c.

Markscheme

a. the antibiotic/ampicillin diffuses out

b. killing bacteria/inhibiting growth of bacteria

c. zone of inhibition/clearing formed

a.

lipid A production/synthesis is not inhibited so bacteria can grow
OR
bacteria grow/are not affected since inhibitor function is lost

b.

no inhibition of growth, since Gram-positive do not have lipid A in membrane/OWTTE

c.

Examiners report

[N/A]

a.

[N/A]

b.

[N/A]

c.

Syllabus sections

Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics) » B.1 Microbiology: organisms in industry

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Option B: Biotechnology and bioinformatics » Option B: Biotechnology and bioinformatics (Core topics)

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