D1.2.8 Features of the genetic code Notes

The Genetic Code is Universal and Degenerate

1. The genetic code is the set of rules by which the information in DNA is translated into proteins.
2. It is nearly universal, degenerate, and specific, ensuring that the right proteins are made at the right time.

Why a Triplet Code?

1. DNA is made up of four bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
2. Proteins, however, are made from 20 different amino acids.
3. So, how does a sequence of four bases code for 20 amino acids?

The Math Behind the Code

1. If each base coded for one amino acid, only four amino acids could be specified.
2. If two bases were used per amino acid, there would be $4^2 = 16$ combinations, still not enough.
3. Using three bases per amino acid provides $4^3 = 64$ combinations, more than enough to cover all 20 amino acids.

Why Is Degeneracy Important?

1. Error Tolerance: Degeneracy helps protect against mutations.
2. Flexibility: It allows for variations in the genetic code without drastically affecting protein function.

Universality of the Genetic Code

1. The genetic code is nearly universal.
2. This means that the same codons specify the same amino acids in almost all organisms, from bacteria to humans.

Why Is Universality Important?

1. Evolutionary Evidence: The universality of the genetic code suggests a common evolutionary ancestor for all life.
2. Biotechnology: It allows scientists to transfer genes between species.
3. For example, human insulin is produced in bacteria using recombinant DNA technology.

Exceptions to Universality

1. While the genetic code is mostly universal, there are rare exceptions.
2. For instance, in some mitochondria, the codon UGA, usually a stop codon, codes for the amino acid tryptophan.