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Question 18N.3.SL.TZ0.10

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Date November 2018 Marks available [Maximum mark: 6] Reference code 18N.3.SL.TZ0.10
Level SL Paper 3 Time zone TZ0
Command term Describe, Explain, Identify, State Question number 10 Adapted from N/A
10.
[Maximum mark: 6]
18N.3.SL.TZ0.10

A section of mRNA contains the start codon for translation of a polypeptide by the ribosomes.

(a)

Identify the nucleotides of the start codon for the polypeptide.

[1]

Markscheme

AUG ✔

(b)

State the chemical difference between the 5' end and the 3' end of a DNA strand.

[1]

Markscheme

5′ end contains a phosphate group «on carbon 5»
OR
3′ carbon contains a hydroxyl/OH group «on carbon 3» ✔

(c)

Within the base sequence shown in the diagram, the sequence for the stop codon UGA appears. Explain the reasons for translation continuing beyond this point in the mRNA.

[2]

Markscheme

a. the gene code occurs in triplets ✔

b. the stop codon would not be part of the reading frame ✔

c. the code for a polypeptide would contain more codons ✔

(d)

Describe how bioinformatics can help identify genes within the DNA of an organism.

[2]

Markscheme

a. bioinformatics is the application of computer technology to biological information
OR
information is stored in a database
OR
bioinformatics is used in analyzing genomes ✔

b. allows for searches/comparisons/analysis of ORF/open reading frame ✔

c. the computer searches for a start codon and a stop codon «and within a distance of 60+ codons» ✔

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