Translation (Part-I)

Introduction: mRNA is the random sequence of nucleotides differentiated by bases attached to them which are Uracil (U), Adenine (A), Cytosine (C), and Guanine (G). Three nucleotides together code for specific amino acid and are called as codons. For example, GAU codes for Asparagine, GGU codes for glycine and so forth. These are called genetic codes. Following is the Figure 30.1, showing genetic code for 20 amino acids.

Figure 30.1 :Genetic code

 

General features of Genetic code

• The genetic code is triplet code called as codon: It is known that we have only 4 types of nucleotides that make the whole genome. It is also known that each codon consists of 3 nucleotides which means there are 4³ = 64 possible amino acids. However, since there are only 20 amino acids it is obvious that more than one codon codes for single amino acid. This also illustrates wobble hypothesis.

• Each coding sequence has start and stop codon to initiate and terminate translation respectively. Usually start codon is AUG which code for methionine and stop codons are UAA, UAG, and UGA. In some cases, starting codons are GUG or UUG.