Give the charecterstics of genetic code only for 11th and 12th students
Answers
i. Genetic code is a triplet code: Sequence
of three consecutive bases constitute
codon, which specifies one particular
amino acid. Base sequence in a codon
is always in 5’ 3’ direction. In every
living organism genetic code is a triplet
code.
ii. Genetic code has distinct polarity :
Genetic code shows definite polarity i.e.
direction. It, therefore, is always read in
5’ 3’ direction and not in 3’ 5’
direction. Otherwise message will change
e.g. 5’ AUG 3’.
iii. Genetic code is non-overlapping : Code
is non overlapping i.e. each single base is
a part of only one codon. Adjacent codons
do not overlap. If non-overlapping, then
with 6 consequtive bases only two amino
acid molecules will be in the chain. Had it
been overlapping type, with 6 bases, there
would be 4 amino acid molecules in a
chain. Experimental evidence is in favour
of non-overlapping nature.
iv. Genetic code is commaless : There is
no gap or punctuation mark between
successive/ consecutive codons.
v. Genetic code has degeneracy : Usually
single amino acid is encoded by single
codon. However, some amino acids are
encoded by more than one codons. e.g.
Cysteine has two codons, while isoleucin
has three codons. This is called degeneracy
of the code. Degeneracy of the code is
explained by Wobble hypothesis. Here,
the first two bases in different codons are
identical but the third one, varies.
vi. Genetic code is universal : By and
large in all living organisms the specific
codon specifies same amino acid. e.g.
codon AUG always specifies amino acid
methionine in all organisms from bacteria
up to humans.
vii. Genetic code is non-ambiguous : Specific
amino acid is encoded by a particular
codon. Alternatively, two different amino
acids will never be encoded by the same
codon.
viii. Initiation codon and termination codon:
AUG is always an initiation codon in any
and every mRNA. AUG codes for amino
acid methionine. Out of 64 codons, three
codons viz. UAA, UAG and UGA are
termination codons which terminate/ stop
the process of elongation of polypeptide
chain, as they do not code for any amino
acid.
ix. Universal : Usually in all organisms the
specific codon specifies same amino acid.
x. Codon and anticodon : Codon is a part
of DNA e.g. AUG is codon. It is always
represented as 5’ AUG 3’.
Answer:
*Genetic code is comma-less
*Code is un-ambigous
*Code is universal
*Code is degenerated