Transcript 7. Protein Synthesis and Translation

Chapter 21 Nucleic Acids and
Protein Synthesis
21.7
Protein Synthesis: Translation
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
1
tRNA Activation
The activation of tRNA
 occurs when a
synthetase uses energy
from ATP hydrolysis to
attach an amino acid to a
specific tRNA
 prepares each tRNA to
use a triplet called an
anticodon to complement
a codon on mRNA
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
2
Initiation of Protein Synthesis
For the initiation of protein synthesis,
 an mRNA attaches to a ribosome
 the start codon (AUG) binds to a tRNA with
methionine
 the second codon attaches to a tRNA with the next
amino acid
 a peptide bond forms between the adjacent amino
acids at the first and second codons
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3
Translocation
During translocation,
 the first tRNA detaches from the ribosome
 the ribosome shifts to the adjacent codon on the
mRNA
 a new tRNA/amino acid attaches to the open
binding site
 a peptide bond forms, and the empty tRNA
detaches
 the ribosome shifts down the mRNA to read the
next codon
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Protein Synthesis
Translation
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Termination of Protein Synthesis
The termination of protein synthesis occurs when
 a polypeptide with all the amino acids for a protein
is synthesized
 the ribosome reaches a “stop” codon: UGA, UAA,
or UAG
 there is no tRNA with an anticodon for the “stop”
codons
 the polypeptide detaches from the ribosome
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Learning Check
Match the following:
1) activation
3) translocation
2) initiation
4) termination
A. Ribosomes move along mRNA, adding amino acids
to a growing peptide chain.
B. A completed peptide chain is released.
C. A tRNA attaches to its specific amino acid.
D. A tRNA binds to the AUG codon of the mRNA on the
ribosome.
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Solution
Match the following:
1) activation
3) translocation
2) initiation
4) termination
3 A. Ribosomes move along mRNA, adding amino
acids to a growing peptide chain.
4 B. A completed peptide chain is released.
1 C. A tRNA attaches to its specific amino acid.
2 D. A tRNA binds to the AUG codon of the mRNA on
the ribosome.
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Summary of Protein Synthesis
To summarize protein synthesis:
 An mRNA attaches to a ribosome.
 Molecules of tRNA bonded to specific amino acids
attach to the codons on mRNA.
 Peptide bonds form between an amino acid and the
peptide chain.
 The ribosome shifts to each codon on the mRNA
until it reaches the STOP codon.
 The polypeptide chain detaches to function as an
active protein.
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Copyright © 2010 Pearson Education, Inc.
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Overview of Protein Synthesis
General, Organic, and Biological Chemistry
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Learning Check
The following section of DNA is used to build an mRNA
for a protein: 3′—GAA—CCC—TTT—5′
A. What is the corresponding mRNA sequence?
B. What are the anticodons on the tRNAs?
C. What is the amino acid order in the peptide?
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Solution
The following section of DNA is used to build an mRNA
for a protein: 3′—GAA—CCC—TTT—5′
A. What is the corresponding mRNA sequence?
5′—CUU—GGG—AAA—3′ mRNA
B. What are the anticodons for the tRNAs?
mRNA codons: CUU GGG AAA
tRNA anticodons: GAA CCC UUU
C. What is the amino acid order in the peptide?
mRNA: 5′—CUU—GGG—AAA—3′
peptide: Leu — Gly — Lys
General, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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