Genetic Code

Genetic Code  - A recapitulation of the relationship between genes and proteins is desirable for an understanding of the genetic code.

1. All metabolic reactions are catalysed by specific enzymes. All enzymes are proteins

2. The action of an enzyme depends upon the sequence of amino acids constituting it

3. The one gene one enzyme hypothesis proposed by Beadle and Tatum in 1940s states that the synthesis of an enzyme is controlled by a particular gene

4. The gene; which is almost always a segment of a DNA strand, transcribes an mRNA strand, which in turn translates a polypeptide chain.

5) Messenger RNA thus acts as an intermediate in conveying information from the sequence of nucleotides in DNA to the sequence of amino acids in the polypeptide chain (Sequence Hypothesis)

6. Each amino acid is specified by a sequence of three bases (the codon) on mRNA

7. Each tRNA molecule has a sequence of three bases (the anticodon) which reads a codon of mRNA. Transfer RNA molecules thus serve as adaptors in proteins synthesis by reading mRNA co dons in a sequence (Crick's Adaptor Hypothesis)

8. The relationship between the sequence of bases in DNA | RNA and the sequence of amino acids in a polypeptide chain is called the genetic code. The code indicates which codons specify which amino acids.