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Cellular Control
Genetics…read more

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The genetic code
· A gene is a series of nucleotide bases, a length of
DNA, that codes for one or several polypeptides.
· Each gene has a specific place (locus) on a
· Each amino acid is coded for by three nucleotide
bases, called a codon.
· Most amino acids are coded for by more than one
· A few codons indicate the end of a gene and are
called stop codons.…read more

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The genetic code…read more

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· The coding strand is the strand of DNA that is
replaced by the RNA nucleotide bases.
· Transcription is the process by which mRNA, a
copy of the coding strand of DNA, is made.
· The template strand is the strand of DNA that
the RNA nucleotide bases bind to.
· The mRNA is complimentary to the DNA
template strand and a copy of the DNA coding
strand.…read more

Slide 5

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1. The gene `unzips' as the hydrogen bonds between
the base pairs are broken. This reaction is
catalysed by the enzyme RNA polymerase.
2. RNA nucleotides bind to their complimentary
bases (A-T, C-G, U-A) on the DNA template strand,
with hydrogen bonds.
3. The phosphoryl groups attached to the RNA
nucleotide bases are broken off and this releases
energy which is used to bind the next nucleotide
base pair…read more

Slide 6

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4. This continues as RNA polymerase moves along
the DNA, until it reaches a stop codon.
5. The RNA then `peels off' as the hydrogen bonds
between the base pairs are broken, producing a
single nucleotide strand.
6. The hydrogen bonds between the DNA strands
then reform.
7. The single nucleotide strand is called mRNA ­
messenger RNA ­ and moves out of the nucleus
through a nuclear pore to a ribosome where the
protein coded for is made in translation.…read more

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