What are the processes of transcription?

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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! 

Lynsey R. GCSE Biology tutor, A Level Physical Education tutor, GCSE ...

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