Answer to Question #138517 in Genetics for man

Question

(c) The DNA molecule codes for the amino acids used to make proteins.

There are four different bases in DNA and 20 amino acids used to make proteins.

Use this information to show that a minimum of three bases on the DNA molecule is needed to code for each amino acid.

Answer 1

It has been established that amino acids are coded by three DNA bases starting from a fixed point; three bases are called a codon. Despite four bases, their arrangement gives rise to a set of 20 amino acids for protein synthesis. The coding sequences are not overlapping, as demonstrated below, to increase the fidelity of amino acid synthesis.

ATGCGTAAT → ATG (amino acid 1, aa1) CGT (aa2) AAT (aa3) etc.,

From the sequence above, the bases are read from base A, which acts as a starting point for amino acid synthesis. Another important feature of genetic code is that some amino acids are encoded by more than one codon since four bases (ATGC) give 64 possible codons, yet there are only 20 amino acids. Genetic code's degenerative nature gives rise to 3 stop codons and 61 codons specifying particular amino acids. The genetic code for all 64 codons is presented in reference below (Berg et al., 2002).

 

Reference

Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 5.5, Amino Acids Are Encoded by Groups of Three Bases Starting from a Fixed Point. Available from: https://www.ncbi.nlm.nih.gov/books/NBK22358/