133299
Description
Mind Map by harry_bygraves, updated more than 1 year ago
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Created by harry_bygraves
over 11 years ago
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How transcription and
translation are regualted
- The genes that are expressed will be continually switched on and off in response to
signals from the cells external and internal enviroments. When the appropriate signals are
recieved, polymerases and other enzymes that transcribe DNA have to be mobilized into
action and locate the correct gene at the right time. After a gene has been transcribed, a
complex series of processes has to take place before the gene is properly expressed
- The effect of oestrogen on gene transcription.
Oestrogen, like other hormones, is transported in the
bloodstream and can reach almost any cell in the body. It
acts as a signal molecule iniating specific cellular
activites, but only in cells that have special oestrogen
receptors onto which it can bind.
- The binding of oestrogen to its receptor molecule is similar to that between a substrate and an enzyme;
both depend on complementary shapes. Being a steriod hormone, oestrogen is soluble in lipids and can
pass through the hydrophobic phospholipid part of the plasma membrane easily. The oestrogen moves
through the cytoplasm and into the nucleus, where it binds to its receptor protein molecule, activating it.
With the oestrogen attached, the active form of the receptor protein becomes a transcriptional factor. A
transcriptional factor is defined as a regulatory protein that binds to DNA and stimulates transcription of
specific genes into mRNA, which directs the synthesis of particular polypetides. In the case of
oestrogen, the oestrogen-receptor complex is the transcriptional factor for a number of different genes,
including those responsible for the development of female secondary characteristics and those involved
in repairing the uterine wall, during the oestrus cycle.
- In this way, oestrogen can have mulitple effects on the body
- In this way, oestrogen can have mulitple effects on the body
- Small interferring RNA (siRNA) consists of pieces of double-stranded RNA,
usually between 19 and 21 nuclotides long, with over hangs of 2 nucleotides
at each 3' end. They are key to a process called RNA interference, the
inhibition of gene expression at the translation stage. The targets for RNA
interference by naturally occuring siRNA's include RNA viruses.
- siRNA acts by having nucleotide sequences complementary to the targeted
mRNA. specific proteins guide siRNA to the target and the siRNA unwinds
so that one strand can combine with the targeted mRNA by complementary
base pairing. After combining, the siRNA interferes with the translation of
the mRNA into a polypeptide thereby stopping expression of the gene
- siRNA's with a tailor-made nucleotide sequence cna be
synthesised. Their ability to selectively silence specific
genes makes them valuable tools in both research and
medicine
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