Transcript DNA and the Genome

Translation
Unit 1: DNA and the Genome
Genetic code
Translation is the synthesis of protein
following the code with in the mature mRNA
transcript.
The mRNA is made of sequences of three
nucleotides (a triplet of bases) called
codons.
Each codon is code for one amino acid.
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DNA and
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DNA and
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tRNA
A further type of RNA is found in the
cell’s cytoplasm.
This is called tRNA (transfer RNA) and is
made of a single chain of nucleotides.
It is folded into a 3D structure, held
together by hydrogen bonds.
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DNA and
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Each tRNA has an attachment site for a
specific amino acid and a triplet of bases
known as an anticodon.
Many different types of tRNA are
present in cell, one or more for each type
of amino acid.
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The tRNA picks up its appropriate amino
acid and takes it to the ribosome to be
matched with the mRNA.
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Ribosomes
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Ribosomes are small, roughly spherical
structures found in all cells.
They contain the enzymes essential for
protein synthesis.
The ribosome’s function is to bring the
tRNA molecules bearing amino acids in
contact with the mRNA.
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Site P – holds the
tRNA carrying the
growing
polypeptide chain.
Site A – holds the
tRNA carrying the
next amino acid to
be joined to the
chain.
Site E – releases the
empty tRNA once it
has dropped off its
amino acid.
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The translation process
1. The ribosome binds to the 5’ end of the
mRNA so that the start codon (AUG) is
in site P.
2. Next a tRNA carrying the amino acid
methionine becomes attached to site P.
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3. The mRNA codon at site A bonds
complementary anticodon on the
appropriate tRNA bearing the correct
amino acid.
4. A peptide bond then forms between
these two amino acids.
5. The ribosome then moves along one codon.
6. The tRNA from Site P is move to Site E
and released.
7. Steps 3-6 then repeat until it reaches a
stop codon.
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DNA and
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Genome