Gene expression

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Gene expression, or simply expression, is the process by which a gene's DNA sequence is converted into the functional proteins of the cell. Non-protein coding genes (e.g. rRNA genes, tRNA genes) are not translated into protein.

Gene expression is a multi-step process that begins with transcription of DNA into messenger RNA (mRNA). Transcription is followed by post transcriptional modification of the amount and timing of appearance of the functional product of a gene. After this, mRNA leaves the cell nucleus. mRNA is then translated by the ribosome to produce a polypeptide. Further changes may then occur through post-translational modification.

Any step of gene expression may be modulated, from the transcription step to post-translational modification of a protein. Gene regulation gives the cell control over structure and function, and is the basis for cellular differentiation, morphogenesis and the versatility and adaptability of any organism.

1 Overexpression
2 Gene networks and expression
3 Techniques
4 See also
5 External links

[edit] Overexpression

In the laboratory, the protein encoded by a gene is sometimes expressed in increased quantity. This can come about by increasing the number of copies of the gene or increasing the binding strength of the promoter region.

Often, the DNA sequence for a protein of interest will be cloned or subcloned into a plasmid containing the lac promoter, which is then transformed into the bacterium Escherichia coli. Addition of IPTG (a lactose analog) causes the bacteria to express the protein of interest. However, this strategy does not always yield functional protein, in which case, other organisms or tissue cultures may be more effective. As for example the yeast, Saccharomyces cerevisiae, is often preferred to bacteria for proteins that undergo extensive Posttranslational modification. Nonetheless, bacterial expression has the advantage of easily producing large amounts of protein, which is required for X-ray crystallography or nuclear magnetic resonance experiments for structure determination.

[edit] Gene networks and expression

Main article: Gene regulatory network

Genes have sometimes been regarded as nodes in a network, with inputs being proteins such as transcription factors, and outputs being the level of gene expression. The node itself performs a function, and the operation of these functions have been interpreted as performing a kind of information processing within cell and determine cellular behaviour.