Coding DNA

Immediately in front of the gene is a region of non-coding DNA. It is described as non-coding because it does not code for the amino acid sequence of the protein. The enzyme RNA polymerase binds to this region, positioning it at the beginning of the gene.

Coding DNA provides instructions for a protein’s structure; some non-coding DNA helps control whether a gene is expressed. The two kinds of variant can therefore affect a characteristic by different routes.

In coding DNA, the sequence of nucleotide bases provides instructions for joining amino acids in a particular order to make a protein. The bases are read in groups of three: each triplet codes for an amino acid. The resulting amino-acid chain then folds into the protein’s particular three-dimensional shape.