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Degree: Human Biosciences (Bachelors) - Exeter University
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Transcription is the first stage of protein synthesis, it occurs in the NUCLEUS.
The main purpose is to make an mRNA (messenger RNA) copy of a gene - it is like a photocopy.
There are 4 main stages....
Number 1) RNA POLYMERASE ATTACHES TO THE DNA
-Transcription cannot start unless RNA polymerase binds to the beginning of the gene, the hydrogen bonds betweeen the two DNA strands break- unwinding the double helix structure.
-One of the strands from the double stranded DNA helix is used as a TEMPLATE.
2) A COMPLEMENTARY STRAND IS FORMED.
-Complementary base pairing occurs, this means A matches with U (Thymine switches to Uracil in RNA) and C matches with G.
-RNA polymerase lines up free nucleotides by the rule mentioned above.
3) RNA POLYMERASE MVOES DOWN THE STRAND
-it moves down the DNA strand and continues to add more free nucleotides until the strand has been created.
-the hydrogen bonds between the uncoiled structure reform and the double helix structure is recreated.
4) mRNA LEAVES THE NUCLEUS
-When RNA polymerase reaches a STOP codon, it stops transcription of the gene.
The RNA polymerase then detaches from the DNA.
-the mRNA moves out of the nucleus via a nuclear pore and attaches to a RIBOSOME in the cytoplasm....this is where TRANSLATION occurs!see more