The genetic code
The genetic code is a set of rules for translating information encoded in DNA into proteins through RNA in genes. The code is read 5' to 3' direction in a fixed reading frame beginning from the start codon (AUG).
The code has the following features:
- codes for a single amino acid whereby the bases are read in sets or groups of 3s called a TRIPLET CODE or CODON.Example is UUU for Phenylalanine, CGC for Arginine.
- is non-overlapping meaning that the triplets (group of 3s) are read separately. A deletion or insertion of bases can cause a frameshift mutation.
- is degenerate- more than one triplet can code for a particular amino acid. This occurs due to redundancy; there are four different bases read in groups of three to give 64 possible combinations but only 20 amino acids ( 43 = 64). Examples are; Serine has the following ( UCU, UCC, UCA, UCG, AGU, AGC), Glycine which has (GGU, GGC, GGA, GGG). These codons are called synonymous codon. However, some amino acid have only one codon which specifies it on the genetic code, example is tryptophan (UGG) and Methionine(AUG), also, the stop codon has three codons which specifies it (UGA, UAA, UAG)
- According Berg et al (2012), "the code lacks punctuation (comma)".
The genetic code is known as universal code but some alterations have been noticed recently. Example is human mitochondrial whereby UGA codes for tryptophan, AGA & AGG code for stop codon; this occurs because mitochondrial DNA encodes a distinct set of tRNAs.
- ↑ Hartl,&amp; Jones,. Genetics: analysis of genes and genomes, 7th Edition(2009) p.g 368. Jones &amp; Bartlett. ISBN 978-0-7637-7216-1
- ↑ Hartl,&amp; Jones,. Genetics: analysis of genes and genomes, 7th Edition(2009) p.g 370. Jones &amp; Bartlett. ISBN 978-0-7637-7216-1
- ↑ Berg JM, Tymoczko JL, &amp; Stryer L. Biochemistry, 7th Edition (2012) p.g 133. Pearson International. ISBN 1-4292-7635-5
- ↑ Berg JM, Tymoczko JL, &amp; Stryer L. Biochemistry, 7th Edition (2012). Pearson International. ISBN 1-4292-7635-5