Isoform

In biochemistry, an isoform refers to genes and their proteins that are created by gene duplications and occur several times in the genome, with some slight changes, or protein variants that are created by alternative splicing . In chemistry, isoform describes a molecule of identical composition, but different structure compared to a second. Some isozymes are isoforms if they not only have the same functions but also have a similar sequence (and genetic relationship). Related genes and pseudogenes that originate from a common gene ancestor through gene duplication are sometimes referred to as isoforms. The scientifically exact term for these genomic isoforms is paralogue .

properties

After a duplication, mutations can result in changes in both originally identical genes, which in some cases also affect the amino acid sequence of the protein. The sequence of a protein also changes in the case of an alternative splicing, for example if the protein is shortened or even more if the reading frame changes . The discovery of many isoforms explains the relatively small number of genes found in the Human Genome Project : the ability to produce many different gene products expands the diversity of the genome many times over. Gene isoforms can be examined using RT-PCR , screening of cDNA banks , Western blots and many other methods.

Examples

Glucokinase (liver; pancreas ) / hexokinase ( ubiquitous ),
Lactate dehydrogenases from skeletal muscle (M-type) or heart muscle (H-type); only the H4 ₄ enzyme is inhibited in the presence of NAD ⁺ and pyruvate .
Creatine kinases have two subunits. KKmm occur specifically in the skeletal muscle , KKbb in the brain and KKmb in the heart muscle . An increased level of the KKmb isoform in the blood indicates e.g. B. clearly indicates a heart attack .

literature

Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0815341062 .

Web links

Entry on Isoform in Flexikon , a Wiki of the DocCheck company

Individual evidence

↑ Guenter Kahl: The Dictionary of Genomics, Transcriptomics and Proteomics. John Wiley & Sons, 2015, ISBN 978-3-527-67864-8 , p. 1136.
↑ John M. Lackie: The Dictionary of Cell and Molecular Biology. Academic Press, 2012, ISBN 978-0-123-84932-8 , p. 344.

[Kahl-1] Guenter Kahl: The Dictionary of Genomics, Transcriptomics and Proteomics. John Wiley & Sons, 2015, ISBN 978-3-527-67864-8 , p. 1136.

[Lackie-2] John M. Lackie: The Dictionary of Cell and Molecular Biology. Academic Press, 2012, ISBN 978-0-123-84932-8 , p. 344.