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Biology Revision Presentation

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An individual's genetic
code is stored in his or her


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"One gene, one
theory states that each
gene on a chromosome
codes for a single

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Protein synthesis begins with
DNA in the nucleus.

The DNA acts as a template for
mRNA which is made using RNA
synthetase from the template
DNA strand.

This process is called

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in transcription the enzyme
DNA helicase works on the cistron
of the DNA breaking the hydrogen
bonds between the two base
strands exposing the nucleotides
in the region.

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RNA polymerase linked to the
template strand of DNA at the
start of the sequence that it
intends to copy.

The DNA is unzipped and
unwound at this point.

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free RNA nucleotides align
themselves with the template
strand following the
complementary pairings:

adenine - uracil,
cytosine - guanine.

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the RNA polymerase molecule
moves along the DNA adding RNA
nucleotides to the mRNA.

Following the RNA polymerase the
DNA 'zips up' and rewinds.

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The mRNA then carries the DNA
code out of the nucleus through a
nuclear pore.

Once in the cytoplasm the mRNA
attaches to a ribosome so that
can take place.

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Each ribosome is made up of two
subunits. Two tRNA molecules
which carry amino acids can be
associated with the ribosome at a

Translation begins with the the
ribosome attaching to the start
codon AUG on the mRNA.


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