Polypeptide Synthesis

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  • Created on: 09-04-13 15:25
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Polypeptide Synthesis
Transcription splicing translation
DNA pre-mRNA mRNA polypeptide
Transcription
1. The enzyme DNA helicase hydrolyses hydrogen bonds in a specific region of the DNA
molecule, causing the 2 strands of the DNA to separate and expose the bases.
2. The enzyme RNA polymerase moves along one DNA strand, the coding (or template)
strand, causing the exposed DNA nucleotides on this strand to join with individual
complimentary DNA nucleotides from the pool in the nucleus.
3. DNA bases = A,C,G,T RNA bases = A,C,G,U
4. RNA polymerase builds a strand of pre-mRNA. Only about 12 base pairs in the DNA are
separated at one time. The DNA molecule joins itself back together behind the RNA
polymerase.
5. When the RNA polymerase reaches a stop base triplet in the DNA it detaches and the
strand of pre-mRNA is complete.
Splicing
DNA is made up of exons and
introns. Exons code for protons
whilst introns do not. In eukaryotic
cells the introns are removed
from the pre-mRNA and the exons
are then joined together. This is
called splicing. The exons can be
joined together in a number of
ways so a single section of DNA
could lead to the production of a

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A splicing
error such as this is believed to cause Alzheimers disease.
Translation
mRNA arrives at a ribosome from the nucelus (via nucelic pores.) Translation takes place at the
ribosomes. Is in this stage in which the codons in the mRNA are converted into a sequence of amino
acids which make up a polypeptide chain.
1. The starting codon (Met)
attaches to the ribosome.
2. The tRNA molecue with a
complimentary anticodon moves to
the ribosome and pairs up with the
mRNA codon.…read more

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