“genetic code”的概念、定义、翻译、参考文献-科学参考

genetic code

Chemistry

A set of rules by which genetic information in nucleic acids is translated into proteins. The information exists in the form of base sequences of messenger RNA, with each amino acid being given by three consecutive RNA bases. Each of these triplets, which are known as codons, is non-overlapping. As there are four types of base in RNA, there are 43434 = 64 possibilities for triplets. Furthermore, as there are about 20 amino acids that commonly occur in proteins, this means that there are several triplets that code for each amino acid. This results in redundancy but not ambiguity. In addition to there being codons for specifying amino acids, there are also codons called start codons and stop codons that start and stop the process of protein construction. The nature of the genetic code was elucidated by Francis Crick and many others in the second half of the 1950s and 1960s. There have been many theories as to how the code evolved into the form that it has, but no consensus on this has yet emerged.

Biology

The means by which genetic information in DNA controls the manufacture of specific proteins by the cell. The code takes the form of a series of triplets of bases in DNA, from which is transcribed a complementary sequence of codons in messenger RNA (see transcription). The sequence of these RNA codons determines the sequence of amino acids during protein synthesis. There are 64 possible codes from the combinations of the four bases present in DNA and messenger RNA and 20 amino acids present in body proteins; also some codons have other functions (see start codon; stop codon; wobble). Hence, the code is redundant: i.e. any given amino acid can be encoded by more than one codon. However, it is not ambiguous—each codon specifies only one amino acid. See illustration.

The genetic code

First base in codon		Second base in codon		Third base in codon
U		C	A	G
U	UUU Phe	UCU Ser	UAU Tyr	UGU Cys	U
	UUC Phe	UCC Ser	UAC Tyr	UGC Cys	C
	UUA Leu	UCA Ser	UAA (stop codon)	UGA (stop codon)^*	A
	UUG Leu	UCG Ser	UAG (stop codon)	UGG Trp	G
C	CUU Leu	CCU Pro	CAU His	CGU Arg	U
	CUC Leu	CCC Pro	CAC His	CGC Arg	C
	CUA Leu	CCA Pro	CAA Gin	CGA Arg	A
	CUG Leu	CCG Pro	CAG Gin	CGG Arg	G
A	AUU lle	ACU Thr	AAU Asn	AGU Ser	U
	AUC lle	ACC Thr	AAC Asn	AGC Ser	C
	AUA lle	ACA Thr	AAA Lys	AGA Arg^†	A
	AUG Met (start codon)	ACG Thr	AAG Lys	AGG Arg	G
G	GUU Val	GCU Ala	GAU Asp	GGU Gly	U
	GUC Val	GCC Ala	GAC Asp	GGC Gly	A
	GUA Val	GCA Ala	GAA Glu	GGA Gly	A
	GUG Val	GCG Ala	GAG Glu	GGG Gly	G

^* UGA encodes tryptophan in mitochondrial DNA

^† AGA is a stop codon in mitochondrial DNA