Use real CAIE Biology questions to translate mutated codons, trace frameshifts or premature stops, and explain how amino-acid changes alter protein folding and function.
Cathelicidin LL-37 is a cell signalling compound that stimulates many different cells in humans. One role of cathelicidin LL-37 is stimulating the production of endothelial cells in the formation of capillaries during wound healing.
Mutations of DNA base sequences in a gene can affect the primary structure of proteins.
Use the information in Table 5.1 and Table 5.2 to suggest the effect on the primary structure of cathelicidin LL-37 of:
the substitution of the base T with the base A in the middle of the triplet at position 5
(TTC to TAC) change from phe to tyr (at position 5) ;
I 'tyr' unqualified
the deletion of base T in the triplet at position 2
Marking guidance:
allow two marks for new sequence is leu arg val ile ser ser gly asp leu ;;
or allow any two from:
I refs to frameshift
1 sequence after, first amino acid / first leu, is different ;
R 'after position 2'
A 'from position 2 onwards'
2 any example ;
e.g. amino acid (at position 2) is arg
3 shortened polypeptide / early chain termination ;
the insertion of base G between bases G and T in the triplet at position 3 .
any two from:
peptide is 3 amino acids in length / shortened polypeptide ;
stop codon in position 4 ;
(third) amino acid is still, gly(cine) / the same ;
Use Table 5.2 to explain why some mutations have no effect on the primary structure of a protein.
any two from:
1 (most) amino acids have more than one, triplet / codon ;
2 any correct example(s) from Table 5.2 ;
if award this then award mp1 as well
3 genetic code is, degenerate / redundant ;
R degenerative / degenerated
4 idea that 64 / 61, possible codons for 20 different amino acids ;
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