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Date	November 2019	Marks available	1	Reference code	19N.2.SL.TZ0.2
Level	Standard level	Paper	Paper 2	Time zone	TZ0 / no time zone
Command term	Outline	Question number	2	Adapted from	N/A

Question

A short base sequence of mRNA and a table of the genetic code are shown below.

Sequence of mRNA

Table of the genetic code

The diagram shows a section of a polypeptide.

Outline the function of codons.

[1]

Determine the sequence of amino acids that could be translated from the sequence of mRNA.

[1]

b.i.

Determine the DNA base sequence transcribed to form this sequence of mRNA.

[1]

b.ii.

Suggest a hypothesis that accounts for the slightly different meaning of some codons in a very limited number of organisms.

[1]

Annotate the diagram to show a peptide bond between two amino acids.

[1]

d.i.

State the type of reaction that removes water while linking amino acids together to form polypeptides.

[1]

d.ii.

Outline the function of Rubisco and of spider silk in relation to their three-dimensional conformation.

[2]

Markscheme

«three bases on mRNA» coding for one amino acid «in a polypeptide» ✔

met-ser-arg-arg
OR
start-ser-arg-arg
OR
met-ser-arg-arg-stop
OR
start-ser-arg-arg-stop ✔

Do not accept peptides containing an amino acid/leu for the last codon.

b.i.

TAC TCG GCT TCC ATC GAC ✔

b.ii.

they occurred after the common origin of life OWTTE
OR
the genetic code is not «in fact» universal ✔

Look for alternatives.

any annotation between a C=O and the next NH ✔

e.g.

d.i.

condensation ✔

Do not accept anabolism alone.

d.ii.

Award [1] per correct row or correct column.

Examiners report

[N/A]

b.i.

[N/A]

b.ii.

[N/A]

d.i.

[N/A]

d.ii.

[N/A]

Syllabus sections

Core » Topic 2: Molecular biology » 2.7 DNA replication, transcription and translation

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