2. Genetic code and ribosomes

Figure 8: Degenerate or redundant codons

Figure 8: Degenerate or redundant codons

2.1 Characteristics of the genetic code

Properties

The promoter is the DNA region bound by RNA polymerase, prior to the start of RNA synthesis. It is made up of one or several conserved sequences marking the beginning of a gene and regulating the level of transcription.

a. Universal: The code is the same for all living organisms.

b. Non-overlapping, unpunctuated:

  • All the nucleotides are used.
  • Each nucleotide is used for a single codon.

c. Degenerate or redundant:

  • 20 different amino acids enter into the composition of proteins.
  • There are 64 different codons.
  • A given amino acid may be encoded by several different codons called synonymous codons.

Note: Generally, in synonymous codons, only the 3rd base varies.