Regulation of gene expression
Gene expression is a process in which the genetic code of a gene aids protein synthesis to produce cell structures. Structural genes are responsible for the coding of amino acid sequences. Because of its role in the human body, gene expression is a tightly controlled process. Proper control of this process is necessary to ensure production of the correct amount of proteins, which the body requires. Thus, regulation of gene expression is important as slight disruptions in the process could result into severe effects, including cancer.
How regulation of gene expression occurs
The needs of the cell largely determine how gene expression is regulated in human body. If the cell were in an environment that requires particular gene products, the expression for that particular cell would increase. Furthermore, cells may produce particular gene products because of external signals or cellular damage. A good example of gene expression regulation is the control of insulin expression to check the level of blood glucose. It is also seen in control of cyclin expression to enhance normal development of the cell cycle. As such, gene regulation plays a major role in determining the overall structure of the cell. It also determines the function, cell differentiation, morphology, and adaptability to the surrounding environment.
Gene expression occurs in two stages, which are transcription and translation. Transcription is whereby genes use enzyme RNA polymerase to synthesize messenger RNA (mRNA) and process the resulting mRNA molecule. On the other hand, translation as a process where mRNA direct protein synthesis and post-translational process that follows. Notably, some genes initiate the production of various forms of RNA, which participate in translation. Examples of these are transfer RNA (tRNA) and ribosomal RNA (rRNA). For these processes to occur effectively and produce appropriate results, regulation of gene expression is necessary.
Gene Control Regions
A structural gene has several components including exons and introns. Exons are responsible for the coding of amino acids and determine the amino acid sequence of the protein. These sections of the gene also feature in the final and developed mRNA molecule. On the other hand, introns are parts of the gene even though they are not responsible amino acids coding. In addition, they are always spliced from mRNA molecule before translation takes place.
Common gene control areas are start site, promoter, enhancers and silencers. A start site refers to the site where transcription takes place. It must have good conditions to allow the process go on uninterruptedly. A promoter is a region that occurs a hundred nucleotides upstream of the gene. Even though this region is not transcribed into mRNA, it plays an important role in regulation of the gene. Transcription factors cleave to particular nucleotide sequences in this region and enhance the binding of RNA polymerases.
On other hand, enhancers are regions where activators bind. Activators are transcription factors, responsible for increasing the rate of transcription, which in turn affects regulation of gene expression. The sites may exist as thousands of nucleotides, stemming from different coding sequences or from an intron. Notably, there are conditional enhancers, which only work in the presence of specific conditions or transcription factors. The last component comprises of the silencers. Repressors bind in this region to depress or disrupt the process of transcription.
Importance of regulation of gene expression
Gene expression sometimes denotes the transcription phase, which we have discussed in the previous section. The amount and type of mRNA molecules present in a cell is a pointer to the function of the cell in the body of a human being. In every second, thousands of transcripts form in every cell. Thus, the control of gene expression starts at the initial stage of protein production, which is the initiation of transcription. MRNA becomes an essential control point since many proteins can come from a single mRNA molecule.
In addition, transcription offers additional regulation of gene expression for eukaryotes in the presence of a nucleus. In prokaryotes, translation takes place before completion of the transcript because of the nearness of ribosome to the mRNA molecule. While this is the case, in eukaryotes, transcripts change in the nucleus before they move to the cytoplasm for translation.
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References:
http://www2.le.ac.uk/departments/genetics/vgec/schoolscolleges/topics/geneexpression-regulation
http://www.nature.com/scitable/topic/gene-expression-and-regulation-15
http://www.news-medical.net/health/Regulation-of-Gene-Expression.aspx