The 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 catalyzed 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 (actually of a polypeptide chain) 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 sequences of nucleotides in DNA to the sequences of amino acids in the polypeptide chain.

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

7. Each tRNA molecules 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 codons in a sequence.

8.The relation ship 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.