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Control of gene expression

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by

Omar Hossam

on 23 October 2012

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Transcript of Control of gene expression

Control of specific gene expression to understand the molecular basis of cell differentiation we need to know how gene can be expressed in a cell-specific manner and how gene get switched on in one cell and not in another Control of transcription by general and tissue specific transcription factor The transcription of a gene is initiated when RNA polymerase binds tightly to the promoter region, with the associated protein it unwinds the DNA helix and start synthesis. Experiment shows that ENHANCER Elements are additional control sites in the DNA which are located at some distance from the start of the transcription that responsible for tissue specific gene expression.

the enhancer elements have different types and position from gene to gene, may be away from the starting point of the transcription by thousands of base pairs, or sited upstream of the gene before the start of the transcription point In Eukaryotic cells, RNA polymerase binding require the co-operation of set of transcription factor which form initial complex with the RNA polymerase at the promoter. the transcription regulators fall into 2 main Groups:

1-General Regulators ( required for the transcription of a wide range of genes and found in almost all cell types )

2-Specific Regulators ( required for specific gene expression or specific set of genes that are tissue specific ) there is an important feature in the control of transcription regulation is the interaction between the enhancers them selves and with other protein and small molecules.

There is an example that 2 ubiquitous transcription factor FOS and JUN . External signals The pattern of gene expression of the cell can be influenced by external signals, such as Steroid hormones that can enter the cell. ( protein growth factors work on the membrane receptor).

Steroid Hormones Effect as a signal:
-Testosterone produced by the testes in mammals and differentiate between male and female. - In insects the Steroid hormone ecdysone responsible for Metamorphosis and induce differentiation in wide variety of cells.

in these cases we see that the hormones can tun a whole of variety of genes in the cell on or off. Storied Hormone signaling A rather different Type of signal transduction pathway which that the signal at the cell surface leads to translocation of transcription factors that are stored as inactive cytoplasmic complex into the nucleus.

these signaling process is specific for protein hormones and growth factors. protein hormone signal transduction models of cell differentiation interaction of transcription factors 3 systems muscle(master genes)
hematopoisis
neural cells differentiation of muscles All blood cells are dived from pluripotant stem cells colony stimulating factor can
direct the differentiation of
neutrophils and macrophages neural crust cells
give several cell types steroid hermon and polypeptide
growth factors specify chromaffin
cells and sympathetic neurons nuclei of different cells can
support egg development
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