In genetics, missense mutations or nonsynonymous mutations are types of point mutations where a single nucleotide is changed to cause substitution of a different amino acid. This in turn can render the resulting protein nonfunctional. Such mutations are responsible for diseases such as Epidermolysis bullosa, sickle-cell disease, and SOD1 mediated ALS(Boillée 2006, p. 39). This article is about the general scientific term. ... A point mutation, or substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide. ... Phenylalanine is one of the standard amino acids. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Sickle-cell disease is a group of genetic disorders caused by sickle hemoglobin (Hgb S or Hb S). ... Structure of the monomeric unit of human superoxide dismutase 2 The enzyme superoxide dismutase (SOD, EC 1. ... Amyotrophic lateral sclerosis (ALS, sometimes called Lou Gehrigs Disease, Maladie de Charcot or motor neurone disease) is a progressive, fatal, neurodegenerative disease caused by the degeneration of motor neurons, the nerve cells in the central nervous system that control voluntary muscle movement. ...

For example, in sickle-cell disease, the 17th nucleotide of the gene for the beta chain of hemoglobin found on chromosome 11 is erroneously changed from the codon GAG (for glutamic acid) to GTG (which codes valine), so the 6th amino acid is incorrectly substituted. A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... Structure of hemoglobin. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... RNA codons. ... Glutamic acid (Glu, E), is the protonated form of glutamate (the anion). ... Valine is an amino acid that cannot be synthesized by humans, so it is considered an essential amino acid for human life. ...

Not all missense mutations lead to appreciable protein changes. An amino acid may be replaced by an amino acid of very similar chemical properties, in which case, the protein may still function normally; this is termed a neutral or "quiet" mutation. When an amino acid may be encoded by more than one codon (so-called "degenerate coding") a mutation in a codon may not produce any change in translation; this would be a synonymous mutation and not a missense mutation. A synonymous substitution (also called a silent substitution) is the evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the amino acid sequence produced is not modified. ...

References

Boillée, Séverine (2006), "ALS: A Disease of Motor Neurons and Their Nonneuronal Neighbors", Neuron 52 (1): 39-59, <http://www.sciencedirect.com/science/article/B6WSS-4M1VCW9-5/2/3d402a1231badda0241595636cb5ad7e>.

See Also

• point mutation