Genetic code

 GENETIC CODE:-

Agentic code is the genetic information in the form of triplet codons on the mRNA which is decoded in a polypeptide chain.

B. Properties of genetic code;
1. Code is triplet:
Suggested for the first time by Gamow and later on confirmed by Nirenberg. The sequence of three consecutive nucleotides makes one codon.
2. Code in non-overlapping:
A base in the m-RNA is never used for two different codons. That means the sequence of sin nitrogenous bases on the m-RNA represents only two codons. For e.g. the sequence UUU. UUC represents only two codons such as UUU & UUC.
3. Code is commaless:
No punctuation marks are present between the triplet codon arranged on m-RNA. It means that on m-RNA triplet codons are arranged in continuous manner or sequence from initiation codon to termination codon.
4. Code is non-ambiguous:
Generally a triplet codon specifies only one type of amino acid. This is called as non-ambiguity of genetic code.
GGA is ambiguous code which specifies two amino acids such as glycine & glutamic acid.
5. Code is universal:
A specific type of code specifies same amino acid in all the types of living organisms either prokaryotes or Eukaryotes.
6. Code is decipherate:
It is possible to know the exact nature of protein molecule because the different codons and the amino acids specified by them can be identified. This is decipheration of code.
7. Code is polarized:
Genetic code shows specific direction which is 5'-3'
8.Code is collinear:
The genetic code decides the sequence of codons on the m-RNA and the corresponding sequence of amino acids molecules in the polypeptide chain. It means that if the sequence of codons is changed the sequence of amino acids and the protein nature will change. This is called as collinearity of genetic code.

Codon & anticodon: -
 A. Codon: A sequence of three consecutive nucleotides present over strand which either specifies amino acid or terminates polypeptide is called as codon.
For e.g.
AUG is initiation codon which specifies methionine in Eukaryotes N-formyl Methionine in prokaryotes.
UAA is a termination codon which brings about termination of synthesis of polypeptide chain.
B. Anticodon: Sequence of three consecutive nucleotides present on central loop of t-RNA and pairs complimentarily with codons present on m-RNA during protein synthesis is called as anticodon or NODOC.
For e.g. If the codon on m-RNA strand is AUG its anticodon will be UAC.

Initiation codon:
It is the sequence of first three consecutive nucleotides present near 5’ end of m-RNA.
It initiates the process of protein synthesis by specifying first amino acid.
Generally, AUG serves as initiation codon. If AUG is absent, GUG serves as initiation codon.
Initiation codon specifies methionine in Eukaryotes and N-formyl methionine in prokaryotes.

Termination codon:

The sequence of three consecutive nucleotides present on m-RNA strand near 3' end is called as termination codon.
It brings about termination of synthesis of polypeptide chain at right stage.
These are also known as nonsense codon as they do not specify any amino acid.These are UAA, UGA & UAG.

WRITE DOWN ALL AMINON ACIDS IN ONE COLUMN AND THEN WRITE DIFFERENT CODONS SPECIFYING THEM. THIS WILL HELP YOU TO REMEMBER THIS TABLE EASILY.