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Cambridge International A Level Biology Revision Guide

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Appendix 2: DNA and RNA triplet codes<br />

The table below shows all the possible triplets of bases in a DNA molecule and what each codes for. The three-letter<br />

abbreviation for each amino acid is, in most cases, the first three letters of its full name (Appendix 1).<br />

First position Second position Third position<br />

A G T C<br />

Phe<br />

Ser<br />

Tyr<br />

Cys<br />

A<br />

A<br />

Phe<br />

Ser<br />

Tyr<br />

Cys<br />

G<br />

Leu<br />

Ser<br />

STOP<br />

STOP<br />

T<br />

Leu<br />

Ser<br />

STOP<br />

Trp<br />

C<br />

G<br />

T<br />

C<br />

Leu<br />

Leu<br />

Leu<br />

Leu<br />

Ile<br />

Ile<br />

Ile<br />

Met<br />

Val<br />

Val<br />

Val<br />

Val<br />

Pro<br />

Pro<br />

Pro<br />

Pro<br />

Thr<br />

Thr<br />

Thr<br />

Thr<br />

Ala<br />

Ala<br />

Ala<br />

Ala<br />

His<br />

His<br />

Gln<br />

Gln<br />

Asn<br />

Asn<br />

Lys<br />

Lys<br />

Asp<br />

Asp<br />

Glu<br />

Glu<br />

Arg<br />

Arg<br />

Arg<br />

Arg<br />

Ser<br />

Ser<br />

Arg<br />

Arg<br />

Gly<br />

Gly<br />

Gly<br />

Gly<br />

A<br />

G<br />

T<br />

C<br />

A<br />

G<br />

T<br />

C<br />

A<br />

G<br />

T<br />

C<br />

The table below shows all the possible triplets of bases in a mRNA molecule and what each codes for.<br />

513<br />

First position Second position Third position<br />

U C A G<br />

Phe<br />

Ser<br />

Tyr<br />

Cys<br />

U<br />

U<br />

Phe<br />

Ser<br />

Tyr<br />

Cys<br />

C<br />

Leu<br />

Ser<br />

STOP<br />

STOP<br />

A<br />

Leu<br />

Ser<br />

STOP<br />

Trp<br />

G<br />

C<br />

A<br />

G<br />

Leu<br />

Leu<br />

Leu<br />

Leu<br />

Ile<br />

Ile<br />

Ile<br />

Met<br />

Val<br />

Val<br />

Val<br />

Val<br />

Pro<br />

Pro<br />

Pro<br />

Pro<br />

Thr<br />

Thr<br />

Thr<br />

Thr<br />

Ala<br />

Ala<br />

Ala<br />

Ala<br />

His<br />

His<br />

Gln<br />

Gln<br />

Asn<br />

Asn<br />

Lys<br />

Lys<br />

Asp<br />

Asp<br />

Glu<br />

Glu<br />

Arg<br />

Arg<br />

Arg<br />

Arg<br />

Ser<br />

Ser<br />

Arg<br />

Arg<br />

Gly<br />

Gly<br />

Gly<br />

Gly<br />

U<br />

C<br />

A<br />

G<br />

U<br />

C<br />

A<br />

G<br />

U<br />

C<br />

A<br />

G

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