Question

Describe the characteristics of genetic code.

Answer 1

Genetic code is the full set of relationships between codons and amino acids (or stop signals). It is basically the way through which the A, C, G and T are strung together.

Complete Answer:
Genetic code is the sequence of nucleotides in DNA and RNA that determines the amino acid sequence of proteins.
i) Commaless: Genetic code is commaless. This means that the arrangement of triplet codons on m-RNA is one after another without a gap.
ii) Non-ambiguous nature: Each codon specifies a particular amino acid. The only exception is AUG which codes for methionine and GUG and codes for valine. But in the absence of AUG, GUG can also code methionine.
iii) Degenerate nature: There are 61 codons for 20 amino acids. But some amino acids are coded by more than one codon. Hence it is said to be degenerated. e.g. GGG, GGA, GGC and GGU all code for glycine.
iv) Polarity: Genetic code could be read only in 5'-3'direction on m-RNA. This polarity is the important aspect of the genetic code. It also has start and stop signals. Start or initiation codon is AUG while UAG, UAA, UGA are the stop or termination codes.
v) Universality: Genetic code is universal for all the organisms from simple bacteria to complex organisms.

Note: The codons in an mRNA can be read during translation. It can be read by beginning with a start codon and continuing until a stop codon is reached. mRNA codons are read from 5' to 3', and they specify the order of amino acids in a protein from N-terminus (methionine) to C-terminus.