Module 1 - Unit 2

  • Created by: S.L.S_10
  • Created on: 12-04-15 12:43

Protein Synthesis - Transcription

Transcription = the creation of a single-stranded mRNA molecule copied from the DNA coding strand. 

Proteins are assembled in the cytoplasm on ribosomes. There are no amino acids in the DNA molecule so a copy of the genetic code has to be made, which can pass through the nuclear pore in the the cytoplasm. The copy is Messenger RNA (mRNA). 

Proteins assembled in the cytoplasm = Internal use (used by the cell - soluble proteins)
Proteins assembled on the RER = External use (use outside the cell - secrectory and membrane proteins)

1) The specific gene on the DNA molecule that is to be copied unzips. The hydrogen bonds between the complementary base pairs breaks and free activated RNA nucleotides in the nucleoplasm temporarily bind to the exposed bases, by hydrogen bonds. 
2) Uracil --> Adenine, Guanine --> Cytosine and Adenine --> Thymine on the TEMPLATE strand. 
3) The sugar-phosphate groups are bonded together to form the sugar-phosphate backbone.
4) RNA polymerase catalyses the binding of RNA nucleotides to the exposed bases. 
5) The two extra phosphates released release energy for the bonding of adjacent nucleotides
6) The mRNA molecule is complementary to the nucleotide base sequence on the template strand of the DNA and is a copy of the coding strand of the length of DNA
7) The mRNA molecule leaves the nucleus through a pore in the nuclear envelope and attaches to a ribosome.

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