What is meant by gene expression and what does control of gene expression mean?

Gene expression refers to genes being ‘turned on’ and producing a product. The product could be an enzyme, a structural protein, or a control molecule. Studies of gene expression typically measure the production of mRNA. Most mechanisms that control gene expression do so by controlling transcription, the synthesis of mRNA. However there are other mechanisms for controlling the rate of protein synthesis that occur downstream (between transcription and translation). Several of these are described in this animation.

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Make sure to use a PC to watch this: http://highered.mheducation.com/sites/9834092339/student_view0/chapter16/control_of_gene_expression_in_eukaryotes.html

1) Transcriptional gene control

https://www.ndsu.edu/pubweb/~mcclean/plsc731/cis-trans/cis-trans6.htm

Any discussion of a promoter and its relevant sequences must consider these sequences and any proteins that may bind to them. Therefore the transcription initiation complex is composed of promoter sequences and DNA binding proteins. These two components of transcription are normally described as cis-acting elements and trans-acting factors.

Cis-acting elements - DNA sequences in the vicinity of the structural portion of a gene that are required for gene expression

Trans-acting factors - factors, usually considered to be proteins, that bind to the cis-acting sequences to control gene expression

2)Translational gene control 

Coming soon

3) Post-translational gene control

Coming soon

DNA - RNA - Protein are formed by replication of DNA , transcription of DNA and translation of mRNA this is knowns as Central dogma of molecular biology. a gene have specific DNA sequence which code for a specific protein by the process of central dogma. when a gene gives protein to do their function it is called gene expression. this mechnaism is very accurate. when a protein produced by gene it do only do required function i.e. only in limit we can say. this is because of gene function in control so this is called gene control.

1) Transcriptional gene control - DNA form RNA in the regulation this is called transcriptinal gene control. this is controlled by various transcriptinal factor. these factor are promoter operator etc. control may be positive or negative. promoter are the site where RNA polymerase bind and operator recognize repressor proteins that bind to a stretch of DNA. for example The enhancer for the promoter of the gene for the delta chain of the gamma/delta T-cell receptor for antigen (TCR) is located close to the promoter for the alpha chain of the alpha/beta TCR (on chromosome 14 in humans). A T cell must choose between one or the other. There is an insulator between the alpha gene promoter and the delta gene promoter that ensures that activation of one does not spread over to the other

2- Translational gene control -refers to the control of the levels of protein synthesized from its mRNA. The corresponding mechanisms are primarily targeted on the control ofribosome recruitment on the initiation codon, but can also involve modulation of the elongation or termination of protein synthesis. example - regulation at the level of termination is fuctional translational readthrough of the lactate dehydrogenase gene LDHB.

3) Post-translational gene control-  Proteins are synthesized by ribosomes translating mRNA into polypeptide chains, which may then undergo PTM to form the mature protein product. this is come under the post translational modification.Post-translational modifications can occur on the amino acid side chains or at the protein's C- or N- termini. this is all about in brief

The central dogma of molecular biology explains how genetic information flows in a biological system. It deals with the sequential and unidirectional order of information. It states that the information flows from DNA (Deoxyribo Nucleic Acid) in the nucleus to RNA (Ribo Nucleic Acid) and from RNA to proteins, in cytoplasm, and the flow is unidirectional.

In other words, the dogma says the following concepts:

DNA can be copied to DNA (DNA replication)

DNA can be copied into mRNA (transcription)

mRNA can encode for proteins (translation)

This concept says that a biopolymer’s sequence is used as a template for the construction of another biopolymer faithfully.

Gene expression means synthesis of proteins from a DNA sequence guided by mRNA. Genes are not always expressed or are expressed at a certain level in the cells. Some genes may be expressed only when the protein product is required by the cells, or when the protein product is not required, gene expression is stopped. Such a switch on and off mechanism of genes is called control of gene expression.

Genes contain certain regions which act as control sites for their expression. A promotor, enhancer, silencer, transcription start site, are all examples of regulatory sites.

Transcriptional gene control is the control or regulation of gene expression at the level of transcription or synthesis of the mRNA. It is the most feasible method for the cell to control gene expression. Repression, CpG methylations, is the examples of transcriptional regulations.

Translational control is the regulation of gene expression at the level of mRNA, like alternate splicing. SiRNA mediated regulation is another example of translational control.

The control of levels of active protein is called post-translational gene control. It is achieved by protein modification like phosphorylation or sequestration or proteolysis.

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