Transcript 8.5 Translation

8.5 Translation
Notes: TRANSLATION
- Step 3 in Protein Synthesis
(Copy everything that is
underlined.)
8.5 Translation
KEY CONCEPT
Translation converts an mRNA message into a
“polypeptide”, or protein - a chain of amino acids.
8.5 Translation
Amino acids are coded by mRNA base sequences.
• Translation converts mRNA messages into “polypeptides”.
• A CODON is a sequence of three nucleotides in the mRNA.
– Each codon codes for an Amino Acid.
codon for
methionine (Met)
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Picture 
codon for
leucine (Leu)
8.5 Translation
Amino Acids are the building blocks
(subunits/monomers) of proteins.
8.5 Translation
• The Genetic Code matches each codon to its amino acid.
The genetic code matches each RNA codon with its amino acid or function.
– There is 1
start
codon(methi
onine)
– There are 3
stop codons
8.5 Translation
• What Amino Acid does each of the following Codons “code
for”?
The genetic code matches each RNA codon with its amino acid or function.
•
•
•
•
AUG?
AAA?
CUU?
GAC?
8.5 Translation
Answers:
• AUG = methionine
(START)
• AAA = lysine
• CUU = leucine
• UGA = STOP
The genetic code matches each RNA codon with its amino acid or function.
8.5 Translation
• A change in the order in which codons are read changes
the resulting protein = mutation.
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Diagrams
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• In all organisms, codons code for the same amino acid.
(DNA is the “universal code”.)
8.5 Translation
• Mutation can be caused by …
– Insertion or deletion of one or more nucleotides
– Substitution of one or more nucleotides.
• This causes a “Frame Shift” – or shift in the way the mRNA
is read (by the ribosome).
8.5 Translation
Amino acids are linked to become a protein.
• Anticodon - a set of three nucleotides that is
complementary to an mRNA codon.
- an anticodon is carried by a tRNA.
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Diagram

8.5 Translation
• Ribosomes consist of two subunits (parts).
– Large subunit has three binding sites where tRNA
molecules attach.
– Small subunit binds to the mRNA.
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Diagram
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8.5 Translation
Steps of translation: (see handout of slides 12 & 13)
1. tRNA binds to a start codon and signals the ribosome to
assemble.
2. A complementary tRNA molecule binds to the exposed
codon, bringing its Amino Acid close to the first amino acid.
8.5 Translation
3. The ribosome helps form a “polypeptide” bond
between the Amino Acids.
4. The ribosome pulls the mRNA strand the length of one
codon.
8.5 Translation
5. Empty tRNA molecule exits the ribosome.
6. A complementary tRNA molecule binds to the next
exposed codon.
7. At the stop codon, the ribosome releases the
protein and disassembles.