Wednesday, January 4, 2012


s the complexity of organisms is increasing the mode of gene regulationmust be complex to control the process of gene expression.
For the process of cell specialization and cell regularity it needs the process of gene regulation for eukaryotic organisms.
The process of gene expression itself is very complex in case of eukaryotic organisms.
Transcription and translation are considered as the basic steps in the process of gene expression
In eukaryotes because of the presence of nucleus seperates transcription from translation in a way not seen in prokaryotes.
Regulation occur at the following steps thus regulating the process of gene regulation in eukaryotes if included
A)At the time of transcription B)While RNA processing C)During the process of m RNA longetivity
These are the major steps when the eukaryotic regulation occur.
Steps involved mRNA processing are A)Addition of 5'cap B)Addition of 3'poly(A)tail C)Removal of introns .
Usually the regulation process occur in any of these steps.
The regulation at this step of transcription /RNA processing is divided into two types. A)Whether RNA must process B)Which exons are retained m RNA.
Regulation step at RNA process indicates/ determines whether the m RNA gets translated/ not .
During this type of regulation of RNA does not get processed it will be transported out of nucleus and will not be translated forever.
In the second type of regulation i.e., which exons are retaived affects the function of the protein produced
Exon shuffling is a process in which some genes have exons that can be exchanged thus by this process the polypeptide produced could have a different function lather than the actual function , this production may some times even cause the premature stopin g of cooling.
Longetivity is the step of degradation of RNA after being processed i.e., the life time of RNA .
The regulation at this step results in the required gene product to be formed rather than other gene product .
For example of two mRNA?s of same langetivity are present and one is made to degrade an hour late than first one by following the process of gene regulation it results in the production of the required ploypeptide more in amount than the other
This is one of the major regulatory step in eukaryotes in which although the mRNA is ready because of this step of regulation the expression of the product cannot occur.
ex: Although mRNA is ready in the egg it does not get expressed until it gets matured.
Instead of repressors and operon system that are present in prokaryotes activation /other wise transcriptional factors paly a major role in transcription control /regulation.
Regulation can be brought by
A)Altering the rate at which RNA transcripts processed.
B)Altering the rate at which mRNA gets degraded
C)Altering the efficiency of translation.
Transcriptional factors are the important protein complexes that help RNA polymerase in binding to DNA.
There are five major types of transcription factor that palys a role in the gene expression like zinc finger proteins , helix turn helix protein , lucin zipper proteins-binding DNA ,helix loop helix-usually then get dimerized.
Steroid receptors In ligand binding thus regulating the activity.
These transcriptional factors which are named as activators ,promoters, enhancers paly a major role in the regulation of the eukaryotic gene expression.
The transcriptional factors whose binding increases the rate of transcription of the gene are called enhancers .
Usually these are located thousand of box pairs away from the gene they control.
Enhancers are usually located upstream ,down stream or even with in the gene they control.
Enhancers binding proteins in addition to their DNA binding site have sites that bind to transcription factors assembled the proteins of the gene .
The length of these enhancer is very short and these enhancers bind to the protein to enhance the transcription levels of genes.
Enhances donot directly act on the promoter region but are bound by activator proteins which usually help in transcribing of genes.
HACNS contributed in evolution keeps in modification in the ankle and foot thus allows human to walk.
Most of the enhancers are located upstream.
Some more enhancers include ECOLI
It is usuallu located 120 bp from the start site contain sites for nitrogen regulatory protein C.
Yeast GAL1 and Gal0 genes
These are some of the enhancers which usually enhance the process of transcription.
Quite Opposite factors to enhances are silencers usually on binding of a transcriptional factor to these of causes the gene expression to be repressed .

These are the regulatory regions located upstream towards 5?region of a gene.
Promoter usually regulates where ,when,and to what level of gene is to be expressed.
Promoter are the regions where the RNA polymerase binds these allowing the process of gene expression to proceed.
In eukaryotes RNA polymerase cannot recognize the promoter by itself then it needs the help of some transcriptional factors which aid in binding to the DNA .

These promoter usually contain specific DNA sequences that are recognized by protein known as transcription factors.
Promoters are processed in both prokaryotes and eukaryotes.
Prokaryotic promoter are the short sequences at -10and -35 positions
These are present upstream from the transcription start site.
Sequence of promoter which is at -10 is called the box with TATAAT nucleotides.
Where are sequence at -35 usually consists of six nucleotides TTGACA.
Eukaryotic promoters cause the DNA to bend back on itself which allows for placement of regulatory sequences.
TATA box lies very close to transcriptional sole in eukaryotes .
Promoters are on broad classified into two types .They are core promoters proximal promoters
This is placed approximately at -34 ,core promoter acts as a binding site RNA polymer.
Uusally this is upstream of the gene that tends to contain primary regulatory elements
It is situated approximately at -250 and is specific for transcription factor binding sites.

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