Gene expression controlled by transcription factors in eukaryotes.

In eukaryotic organisms...

every cell has the same genome, but they all use it differently as different genes are expressed in different cells at different times.

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What are transcription factors?

Proteins or short, non-coding pieces of RNA. They may aid or inhibit the binding of RNA polymerase to DNA promoter regions to activate or suppress gene expression.

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What do tumour suppressors and proto-oncogenes do?

help regulate cell division by coding for transcription factors.

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First step of how transcription factors work:

genes in DNA can be transcribed into mRNA

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Second step:

transcription is initiated by the enzyme RNA polymerase and transcription factors binding to the DNA.

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Third step:

they bind to an area called the promoter region-a section of DNA adjacent to the gene to be transcribed.

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Fourth step:

the RNA polymerase and transcription factors (transcription initiation complex) must form and correctly attach to the DNA for transcription to proceed.

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First step of switching genes ON using transcription factors:

Some TF are always present in all cells whilst some are only synthesised in particular cells or at a particular stage of development.Many are created in an inactive form and made active by signal molecules eg. hormones and growth factors.

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How can the action of transcription factors be regulated by other molecules?

molecules like oestrogen(lipid soluble, steroid molecule) can diffuse through plasma membrane of cell and bind to a site on a TF.The active site on the TF will have a complimentary shape to oestrogen. This can change the shape of the TF.

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What does this do to the TF?

It activates the TF, meaning it can get inside the nucleus through a nuclear pore and can now bind to part of the DNA that it needs to bind to, then activate transcription. This is done by increasing the affinity of RNA polymerase to the promoter reg

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Second step:

the gene remains switched off until all the required transcription factors are present in their active forms.The TIC can then form and attach to the promoter region successfully.

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Switching genes OFF using transcription factors:

Transcription can be prevented by protein repressor molecules attaching to the promoter region. This blocks the attachment sites for TF &/or stops the TIC from binding.

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What can protein repressor molecules also bind to, to prevent transcription?

can also bind to transcription factors, stopping the transcription initiation complex from forming.

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Gene expression controlled by transcription factors in eukaryotes.

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