A-LevelBiologyNucleic acids and protein synthesis9700/21 · May/June 2019 · Q69 Marks

The DNA in the nucleus is known as nuclear DNA.

(a)(i)In the cells of the grasshopper, Chorthippus brunneus, 20% of the nucleotides in nuclear DNA contain thymine. Calculate the percentage of nucleotides in the nuclear DNA of C. brunneus that contain guanine and explain your answer in terms of the structure of DNA. percentage explanation[3]
(a)(ii)State another location, other than the nucleus, where DNA occurs in cells of C. brunneus.[1]
(b)(i)Fig. 6.1 is a diagram of a molecule of tRNA. The region labelled R shows detail of part of the tRNA molecule. Complete Fig. 6.1 by writing the sequence of bases in the region labelled R.[1]
(b)(ii)State the name of region Q and explain the role of region Q in translation. name explanation[3]
(b)(iii)State the function of region P.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

30%; A anywhere in the answer
bases, are paired / are complementary ; A with ref. to binding
A hydrogen bonds between, A and T/C and G
A thymine or T pairs with adenine or A/cytosine or C pairs with guanine or G
calculation / explanation for 30% ; e.g. A+T = 40%, C+G = 60%, half of 60% = 30%
mitochondria / mitochondrion (in cytoplasm);
R whole answer if anything else is first or second in answer
R 'mitochondria and / or cytoplasm'
G
G
U
C;
anticodon;
any two from:
Q/anticodon, binds / AW, to, codon on mRNA ;
I ref. to complementary bases alone
idea that specificity ensures correct primary structure (of polypeptide / protein);
A correct amino acid sequence (of polypeptide / protein)
site of attachment of (specific) amino acid (to tRNA) / amino acid binding site ;

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