Curricular Resources > 1999 Volume V > Unit 2 (99.05.02) > Section 14

How Do You Know? The Experimental Basis of Chemical Knowledge

The Amazing DNA Molecule: Its History, Structure and Function

Monique Yvonne Gisser

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APPENDIX D

The Genetic Code

The genetic code is redundant. That is there are 64 possible combinations of the 4 different bases yet there are only 20 common amino acids. More than one codon will code for the same amino acid or function. This redundancy in the code is often called degeneracy.

Each codon is a segment of DNA. DNA is transcribed by RNA polymerase into messenger RNA, therefore sometimes you may see a genetic code where uracil (U) is substituted for thymine (T). Although this code presented uses the four DNA nitrogenous bases (A, C, G, and T), please note that it could be considered more appropriate to use the four RNA nitrogenous bases (A, C, G, and U) since the messenger RNA transcript is what is being decoded during translation.

(1st base)

(2nd)

(3rd)

A	AAA Lys	CAA Gln	GAA Glu	TAA stop	A
	AAC Asn	CAC His	GAC Asp	TAC Tyr	C
	AAG Lys	CAG Gln	GAG Glu	TAG stop	G
	AAT Asn	CAT His	GAT Asp	TAT Tyr	T

C	ACA Thr	CCA Pro	GCA Ala	TCA Ser	A
	ACC Thr	CCC Pro	GCC Ala	TCC Ser	C
	ACG Thr	CCG Pro	GCG Ala	TCG Ser	G
	ACT Thr	CCT Pro	GCT Ala	TCT Ser	T

G	AGA Arg	CGA Arg	GGA Gly	TGA stop	A
	AGC Ser	CGC Arg	GGC Gly	TGC Cys	C
	AGG Arg	CGG Arg	GGG Gly	TGG Trp	G
	AGT Ser	CGT Arg	GGT Gly	TGT Cys	T

T	ATA Ile	CTA Leu	GTA Val	TTA Leu	A
	ATC Ile	CTC Leu	GTC Val	TTC Phe	C
	ATG*Met	CTG Leu	GTG Val	TTG Leu	G
	ATT Ile	CTT Leu	GTT Val	TTT Phe	T

*ATG will code for either START if at the beginning of transcript or for Met if inside the transcript

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