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Synthesising a polypeptide:
1
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2
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This tRNA carries a specific amino acid
(methionine)
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4
...


In summary, the DNA sequence of triplets that make up a gene determine the sequence of codons on mRNA
...
They then in turn determine the sequence of amino acids in the polypeptide
...


A tRNA molecule with a complementary anticodon (UGC) pairs
with the next codon on the mRNA (ACG)
...

Translation
The ribosome moves along the mRNA, bringing together two
tRNA molecules at any one time, each pairing up with the corresponding two codons on the mRNA
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6
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7
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8
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9
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10
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At this point, the ribosome, mRNA and

Assembling a protein:

Sometimes a single polypeptide chain is a functional protein
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What happens to the polypeptide next
depends on the protein being made but usually involves:
•

the polypeptide is coiled or folded, producing its secondary
structure
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•

Different polypeptide chains, along with any non-protein
groups, are linked to form the quaternary structure
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They did so by making synthetic mRNA and using this to
make polypeptides
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cell extracts with the necessary components to make polypeptides were obtained and treated with DNase
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Synthetic mRNA was added to the extract and all 20 amino acids attached to their appropriate tRNA
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One amino acid was radioactively labelled with Carbon 14 (14C)
while the remaining 19 had normal, non-radioactive carbon 12
(12C)
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The extracts were incubated and the polypeptide produced was
later extracted
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The radioactivity level of the polypeptide produced in each case
was measured
...
The
remaining 17 gave ambiguous results

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