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Chapter 9
• Gene Expression and Regulation
Copyright © 2006 Pearson Prentice Hall, Inc.
9.1 How Is the Information in
DNA Used in a Cell?
• 9.1.1 Most Genes Contain Information
for the Synthesis of a Single Protein
• 9.1.2 RNA Intermediaries Carry the
Genetic Information for Protein
Synthesis
– Table 9.1 A Comparison of DNA and RNA
(p. 126)
Copyright © 2006 Pearson Prentice Hall, Inc.
Copyright © 2006 Pearson Prentice Hall, Inc.
9.1 How Is the Information in
DNA Used in a Cell?
• 9.1.3 Overview: Genetic Information Is
Transcribed into RNA, Then Translated
into Protein
– Figure 9.1 Genetic information flows from
DNA to RNA to protein (p. 126)
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gene
DNA
(nucleus)
(cytoplasm)
(a) Transcription
messenger RNA
(b) Translation
ribosome
protein
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9.2 What Is the Genetic
Code?
• 9.2.1 A Sequence of Three Bases
Codes for an Amino Acid
– Table 9.2 The Genetic Code (Codons of
mRNA) (p. 127)
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Copyright © 2006 Pearson Prentice Hall, Inc.
9.3 How Is the Information in
a Gene Transcribed into
RNA?
• 9.3.1 Transcription Begins When RNA
Polymerase Binds to the Promoter of a
Gene
– Figure 9.2 Transcription is the synthesis of
RNA from instructions in DNA (p. 128)
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DNA
gene 1
gene 2
gene 3
Initiation
DNA
RNA
polymerase
promote
r
RNA polymerase binds to the promoter region of DNA near the beginning of a gene, separating the double helix near
the promoter.
Elongation
RNA
DNA template strand
RNA polymerase travels along the DNA template strand, catalyzing the addition of ribose nucleotides into an RNA
molecule. The nucleotides in the RNA are complementary to the template strand of the DNA.
Termination
termination signal
At the end of a gene, RNA polymerase encounters a sequence of DNA called a termination signal. RNA polymerase
detaches from the DNA and releases the RNA molecule.
Conclusion of transcription
RNA
After termination, the DNA completely rewinds into a double helix. The RNA molecule is free to move from the
nucleus to the cytoplasm for translation, and RNA polymerase may move to another gene and begin transcription
once again.
Copyright © 2006 Pearson Prentice Hall, Inc.
DNA
gene 1
gene 2
gene 3
Initiation
DNA
RNA
polymerase
promoter
RNA polymerase binds to the promoter region of DNA near the beginning of a gene, separating the double helix near
the promoter.
Copyright © 2006 Pearson Prentice Hall, Inc.
Elongation
RNA
DNA template strand
RNA polymerase travels along the DNA template strand, catalyzing the addition of ribose nucleotides into an RNA
molecule. The nucleotides in the RNA are complementary to the template strand of the DNA.
Copyright © 2006 Pearson Prentice Hall, Inc.
Termination
termination signal
At the end of a gene, RNA polymerase encounters a sequence of DNA called a termination signal. RNA polymerase
detaches from the DNA and releases the RNA molecule.
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Conclusion of transcription
RNA
After termination, the DNA completely rewinds into a double helix. The RNA molecule is free to move from the
nucleus to the cytoplasm for translation, and RNA polymerase may move to another gene and begin transcription
once again.
Copyright © 2006 Pearson Prentice Hall, Inc.
9.3 How Is the Information in
a Gene Transcribed into
RNA?
• 9.3.2 Elongation Generates a Growing
Strand of RNA
– Figure 9.3 RNA transcription in action (p.
129)
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RNA transcription
gene
RNA
molecules
DNA
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9.3 How Is the Information in
a Gene Transcribed into
RNA?
• 9.3.3 Transcription Stops When RNA
Polymerase Reaches the Termination
Signal
• 9.3.4 Transcription Is Selective
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9.4 What Are the Functions of
RNA?
• Figure 9.4 Cells synthesize three major
types of RNA (p. 130)
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Messenger RNA (mRNA)
Ribosome: contains
ribosomal RNA
(rRNA)
large
subunit
catalytic site
tRNA/amino acid
binding sites
small
subunit
Transfer RNA (tRNA)
tyr
attached
amino acid
anticodon
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Messenger RNA (mRNA)
Copyright © 2006 Pearson Prentice Hall, Inc.
Ribosome: contains
ribosomal RNA
(rRNA)
large
subunit
small
subunit
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catalytic site
tRNA/amino acid
binding sites
Transfer RNA (tRNA)
tyr
attached
amino acid
anticodon
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9.4 What Are the Functions of
RNA?
• 9.4.1 Messenger RNA Carries the
Code for a Protein from the Nucleus to
the Cytoplasm
• 9.4.2 Ribosomal RNA and Proteins
Form Ribosomes
• 9.4.3 Transfer RNA Molecules Carry
Amino Acids to the Ribosomes
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9.5 How Is the Information in
Messenger RNA Translated
into Protein?
• 9.5.1 Translation Begins When tRNA
and mRNA Bind to a Ribosome
– Figure 9.5 Translation is the process of
protein synthesis (p. 132)
Copyright © 2006 Pearson Prentice Hall, Inc.
Initiation:
amino acid
second tRNA binding site
catalytic site
met
met
tRNA
initiation
complex
methionine
tRNA
mRNA
large
ribosomal
subunit
first tRNA
binding
site
small
ribosomal
subunit
A tRNA with an attached methionine
amino acid binds to a small
ribosomal subunit, forming
an initiation complex.
The initiation complex binds to an
mRNA molecule. The methionine
(met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of
the mRNA.
The large ribosomal subunit binds
to the small subunit. The methionine
tRNA binds to the first tRNA site on
the large subunit.
Elongation:
catalytic site
The second codon of mRNA
(GUU) base-pairs with the
anticodon (CAA) of a second
tRNA carrying the amino acid
valine (val). This tRNA binds to
the second tRNA site on the
large subunit.
catalytic site
initiator
peptide tRNA detaches
bond
The catalytic site on the large subunit
catalyzes the formation of a peptide
bond linking the amino acids methionine
and valine. The two amino acids are now
attached to the tRNA in the second
binding position.
ribosome moves one codon to right
The "empty" tRNA is released and
the ribosome moves down the mRNA,
one codon to the right. The tRNA that
is attached to the two amino acids is
now in the first tRNA binding site and
the second tRNA binding site is empty.
Termination:
catalytic site
completed
peptide
stop codon
The third codon of mRNA (CAU)
base-pairs with the anticodon
(GUA) of a tRNA carrying the
amino acid histidine (his). This
tRNA enters the second tRNA
binding site on the large subunit.
The catalytic site forms a new
peptide bond between valine
and histidine. A three-aminoacid chain is now attached to
the tRNA in the second binding
site. The tRNA in the first site
leaves, and the ribosome moves
one codon over on the mRNA.
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This process repeats until a
stop codon is reached; the
mRNA and the completed
peptide are released from the
ribosome, and the subunits
separate.
Initiation:
amino acid
met
met
catalytic site
second tRNA
binding site
tRNA
initiation
complex
methionine
tRNA
mRNA
first tRNA
binding
site
large
ribosomal
subunit
small
ribosomal
subunit
A tRNA with an attached methionine
amino acid binds to a small
ribosomal subunit, forming
an initiation complex.
The initiation complex binds to an
mRNA molecule. The methionine
(met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of
the mRNA.
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The large ribosomal subunit binds
to the small subunit. The methionine
tRNA binds to the first tRNA site on
the large subunit.
amino acid
met
methionine
tRNA
initiation
complex
small
ribosomal
subunit
A tRNA with an attached methionine
amino acid binds to a small
ribosomal subunit, forming
an initiation complex.
Copyright © 2006 Pearson Prentice Hall, Inc.
met
tRNA
mRNA
The initiation complex binds to an
mRNA molecule. The methionine
(met) tRNA anticodon (UAC) basepairs with the start codon (AUG) of
the mRNA.
Copyright © 2006 Pearson Prentice Hall, Inc.
catalytic site
first tRNA
binding
site
second tRNA binding site
large
ribosomal
subunit
The large ribosomal subunit binds
to the small subunit. The methionine
tRNA binds to the first tRNA site on
the large subunit.
Copyright © 2006 Pearson Prentice Hall, Inc.
Elongation:
catalytic site
catalytic site
peptide
bond
initiator
tRNA detaches
ribosome moves one codon to right
The second codon of mRNA
(GUU) base-pairs with the
anticodon (CAA) of a second
tRNA carrying the amino acid
valine (val). This tRNA binds to
the second tRNA site on the
large subunit.
The catalytic site on the large subunit
catalyzes the formation of a peptide
bond linking the amino acids methionine
and valine. The two amino acids are now
attached to the tRNA in the second
binding position.
Copyright © 2006 Pearson Prentice Hall, Inc.
The "empty" tRNA is released and
the ribosome moves down the mRNA,
one codon to the right. The tRNA that
is attached to the two amino acids is
now in the first tRNA binding site and
the second tRNA binding site is empty.
catalytic site
The second codon of mRNA
(GUU) base-pairs with the
anticodon (CAA) of a second
tRNA carrying the amino acid
valine (val). This tRNA binds to
the second tRNA site on the
large subunit.
Copyright © 2006 Pearson Prentice Hall, Inc.
peptide
bond
The catalytic site on the large subunit
catalyzes the formation of a peptide
bond linking the amino acids methionine
and valine. The two amino acids are now
attached to the tRNA in the second
binding position.
Copyright © 2006 Pearson Prentice Hall, Inc.
catalytic site
initiator
tRNA detaches
ribosome moves one codon to right
The "empty" tRNA is released and
the ribosome moves down the mRNA,
one codon to the right. The tRNA that
is attached to the two amino acids is
now in the first tRNA binding site and
the second tRNA binding site is empty.
Copyright © 2006 Pearson Prentice Hall, Inc.
Termination:
catalytic site
completed
peptide
stop codon
The third codon of mRNA (CAU)
base-pairs with the anticodon
(GUA) of a tRNA carrying the
amino acid histidine (his). This
tRNA enters the second tRNA
binding site on the large subunit.
The catalytic site forms a new
peptide bond between valine
and histidine. A three-aminoacid chain is now attached to
the tRNA in the second binding
site. The tRNA in the first site
leaves, and the ribosome moves
one codon over on the mRNA.
Copyright © 2006 Pearson Prentice Hall, Inc.
This process repeats until a
stop codon is reached; the
mRNA and the completed
peptide are released from the
ribosome, and the subunits
separate.
catalytic site
The third codon of mRNA (CAU)
base-pairs with the anticodon
(GUA) of a tRNA carrying the
amino acid histidine (his). This
tRNA enters the second tRNA
binding site on the large subunit.
Copyright © 2006 Pearson Prentice Hall, Inc.
The catalytic site forms a new
peptide bond between valine
and histidine. A three-aminoacid chain is now attached to
the tRNA in the second binding
site. The tRNA in the first site
leaves, and the ribosome moves
one codon over on the mRNA.
Copyright © 2006 Pearson Prentice Hall, Inc.
completed
peptide
stop codon
This process repeats until a
stop codon is reached; the
mRNA and the completed
peptide are released from the
ribosome, and the subunits
separate.
Copyright © 2006 Pearson Prentice Hall, Inc.
9.5 How Is the Information in
Messenger RNA Translated
into Protein?
• 9.5.2 Elongation Generates a Growing
Chain of Amino Acids
• 9.5.3 A Stop Codon Signals
Termination
– Figure 9.6 Complementary base pairing is
critical to decoding genetic information (p.
133)
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gene
DNA
etc.
complementary
DNA strand
template DNA
strand
etc.
codons
mRNA
etc.
anticodons
tRNA
etc.
amino acids
protein
methionine
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glycine
valine
etc.
gene
DNA
complementary
DNA strand
template DNA
strand
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etc.
etc.
codons
mRNA
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etc.
tRNA
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etc.
amino acids
protein
methionine
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glycine
valine
etc.