DNA nonsense point mutation. Animation showing a nonsense point mutation in the replication of DNA (deoxyribonucleic acid). As the DNA unravels, a helicase enzyme (red) is shown moving along the helix, separating the complementary strands. Labels appear showing the genetic code, the sequence of the nucleotide bases along a strand (cytosine, C, blue; guanine, G, yellow; adenine, A, green; thymine, T, red). A DNA polymerase enzyme is shown replicating a new strand and making a mistake (red area). The new complementary strands are formed, completing the replication process and the animation zooms in on the mistake (a mutation). Adjacent groups of three bases, known as codons, code for the production of amino acids (the basis of proteins). The codon affected here is GGA (for the amino acid glycine). This has mutated to TGA, which is a stop codon. This truncates the protein production, causing abnormal shortening. This is known as a nonsense mutation, as opposed to mutations that produce change (a missense mutation) or no change (a silent mutation). |