What are the processes of transcription?

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!