Transcript Chapter 8

Chapter 8
Section 8.5: Translation
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Objectives
• SWBAT describe how mRNA codons are
translated into amino acids.
• SWBAT summarize the process of protein
synthesis.
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Vocabulary
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Translation
Codon
Stop codon
Start codon
Anticodon
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The Process of Translation
• Translation is the process that converts, or
translates, an mRNA message into a
polypeptide.
– One or more polypeptide chains make up a
protein.
• While DNA and RNA only use four nucleotides
each in their codes, the language of proteins
uses 20 amino acids.
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Triplet Code
• A codon is a threenucleotide RNA
sequence that codes
for an amino acid.
• The genetic code
matches each codon
to its amino acid or
function (the
start/stop codons).
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Triplet Code
Methionine
is the start
codon while
there are
three stop
codons.
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Triplet Code – for Amino Acids
• A change in the order
in which codons are
read changes the
resulting protein.
• Regardless of the
organism, codons
code for the same
amino acid.
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Anticodon
• An anticodon is a set of
three nucleotides that
is complementary to an
mRNA codon (a codon
of CCC binds with an
anticodon of GGG).
• An anticodon is carried
by a tRNA.
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Ribosomes (rRNA)
• The large and small
ribosomal subunits
pull mRNA through
the ribosome,
reading it one codon
at a time.
• The large subunit
has three binding
sites for tRNA’s
anticodon.
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Translation
For translation to begin, tRNA binds to a start codon and signals the ribosome to
assemble.
A complementary tRNA molecule binds to the exposed codon, bringing its amino
acid close to the first amino acid.
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Translation
• The ribosome helps form a polypeptide bond between the amino
acids.
• The ribosome pulls the mRNA strand the length of one codon.
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Translation
• The now empty tRNA molecule exits the ribosome.
– A complementary tRNA molecule binds to the next exposed
codon.
– Once the stop codon is reached, the ribosome releases the
protein and disassembles.
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