Question

mention the characteristics of genetic code?

Answer 1

The code is a triplet codon:

The nucleotides of mRNA are arranged as a linear sequence of codons, each codon consisting of three successive nitrogenous bases, i.e., the code is a triplet codon. The concept of triplet codon has been supported by two types of point mutations: frame shift mutations and base substitutions.

Frameshift mutations:

Evidently, the genetic message once initiated at a fixed point is read in a definite frame in a series of three letter words. The framework would be disturbed as soon as there is a deletion or addition of one or more bases.

When such frame shift mutations were intercrossed, then in certain combinations they produce wild type normal gene. It was concluded that one of them was deletion and the other an addition, so that the disturbed order of the frame due to mutation will be restored by the other

 Base substitution:

If in a mRNA molecule at a particular point, one base pair is replaced by another without any deletion or addition, the meaning of one codon containing such an altered base will be changed. In consequence, in place of a particular amino acid at a particular position in a polypeptide, another amino acid will be incorporated.

The code is non-ambiguous:

Non-ambiguous code means that a particular codon will always code for the same amino acid. In case of ambiguous code, the same codon could have different meanings or in other words, the same codon could code two or more than two different amino acids. Generally, as a rule, the same codon shall never code for two different amino acids.

However, there are some reported exceptions to this rule: the codons AUG and GUG both may code for methionine as initiating or starting codon, although GUG is meant for valine. Likewise, GGA codon codes for two amino acids glycine and glutamic acid.

The code is degenerate:

More than one codon may specify the same amino acid; this is called degeneracy of the code. For example, except for tryptophan and methionine, which have a single codon each, all other 18 amino acids have more than one codon. Thus, nine amino acids, namely phenylalanine, tyrosine, histidine, glutamine, asparagine, lysine, aspartic acid, glutamic acid and cysteine, have two codons each. Isoleucine has three codons. Five amino acids, namely valine, proline, threonine, alanine and glycine, have four codons each. Three amino acids, namely leucine, arginine and serine, have six codons each

Answer 2

Answer:

1. degenerate
2. universal
3. triplet nature