- Created by: Ahmra
- Created on: 04-03-13 12:37
Nature of the Genetic Code
DNA acts as a store of genetic information.
Chromosomes are divided up Into thousands of shorter sections called Genes.
The length of DNA making up a particular gene carries the information needed to make a particular protein.
This information is called the Genetic Code.
The code carried by DNA determines what reactions can take place in an organism . Genes control the formation of enzymes which are proteins.
By deterimining which enzymes are produced the DNA can determine the characteristics of an organism.
DNA is the starting point for protein synthesis since the sequence of bases on DNA , the Genetic Code, determines the primary structure of a protein ,that is ,the sequence by which various amino acids are joined together to form a particular polypeptide chain.
Why is the Code a Triplet Code ?
Each amino acid must have its own code of bases on the DNA.
There are four different bases in DNA ( Adenine, Thymine, Guanine and Cytosine ) but there are over 20 different amino acids.
If one base coded for one amino acid it would be possible to make only 4 amino acids. If two bases coded for one amino acid it would be possible to produce 16 different codes to make 16 amino acids.
Having three bases for each amino acid would give a permutation of 64 codes more than enough to make 20 different amino acids. As the code has three bases it is called a Triplet Code.
Amino acids are in fact coded by more than one DNA base triplet. Some codes do not code for amino acids at all. They are stop and start codes.
It is the sequence of bases in the DNA chain that codes for the sequence of amino acids in a polypeptide. The portion of DNA which codes for a whole polypeptide chain is called a Gene. One Gene = One Polypeptide Hypothesis.
Each amino acid is coded for three bases ( Triplet Code ) called a Codon. All Codons are Universal, that is, they are exactly the same for all living organisms. The Code is Non-Overlapping in that each triplet is read separately.