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Third mRNA base (3 end of codon)
First mRNA base (5 end of codon)
Fig. 17-5
Second mRNA base
the mechanism of translation
Amino
acids
Polypeptide
Ribosome
tRNA with
amino acid
attached
tRNA
Anticodon
Codons
5
mRNA
3
Fig. 18-3a
trp operon
Promoter
Promoter
Genes of operon
DNA
trpR
Regulatory
gene
mRNA
Protein
5
trpE
3
Operator
Start codon
mRNA 5
RNA
polymerase
Inactive
repressor
(a) Tryptophan absent, repressor inactive, operon on
E
trpD
trpC
trpB
trpA
B
A
Stop codon
D
C
Polypeptide subunits that make up
enzymes for tryptophan synthesis
Fig. 18-2
Precursor
trpE gene
Enzyme 1
trpD gene
Enzyme 2
trpC gene
trpB gene
Enzyme 3
trpA gene
Tryptophan
(a) Regulation of enzyme
activity
(b) Regulation of enzyme
production
Fig. 18-3a
trp operon
Promoter
Promoter
Genes of operon
DNA
trpR
Regulatory
gene
mRNA
Protein
5
trpE
3
Operator
Start codon
mRNA 5
RNA
polymerase
Trp
repressor
(a) Tryptophan absent, repressor inactive, operon on
E
trpD
trpC
trpB
trpA
B
A
Stop codon
D
C
Polypeptide subunits that make up
enzymes for tryptophan synthesis
Fig. 18-3b-2
DNA
No RNA made
mRNA
Protein
Active
repressor
Tryptophan
(corepressor)
(b) Tryptophan present, repressor active, operon off
The actual structure of the Trp Repressor
Fig. 18-4b
The lac operon
lac operon
DNA
lacZ
lacI
3
mRNA
5
mRNA 5
-Galactosidase
Allolactose
(inducer)
lacA
RNA
polymerase
Protein
Lac Repressor
lacY
Inactive
repressor
(b) Lactose present, repressor inactive, operon on
Permease
Transacetylase
Fig. 18-4a
Regulatory
gene
Promoter
Operator
lacI
DNA
lacZ
No
RNA
made
3
mRNA
5
Protein
RNA
polymerase
Active
repressor
(a) Lactose absent, repressor active, operon off
Fig. 18-4b
lac operon
DNA
lacZ
lacI
3
mRNA
5
lacA
RNA
polymerase
mRNA 5
-Galactosidase
Protein
Allolactose
(inducer)
lacY
Inactive
repressor
(b) Lactose present, repressor inactive, operon on
Permease
Transacetylase
Fig. 18-5
Promoter
Operator
DNA
lacI
lacZ
CAP-binding site
RNA
polymerase
binds and
transcribes
Active
CAP
cAMP
Inactive
CAP
Inactive lac
repressor
Allolactose
(a) Lactose present, glucose scarce (cAMP level
high): abundant lac mRNA synthesized
Promoter
DNA
Operator
lacI
CAP-binding site
Inactive
CAP
lacZ
RNA
polymerase less
likely to bind
Inactive lac
repressor
(b) Lactose present, glucose present (cAMP level
low): little lac mRNA synthesized
Fig. 18-5
Promoter
Operator
DNA
lacI
lacZ
CAP-binding site
RNA
polymerase
binds and
transcribes
Active
CAP
cAMP
Inactive
CAP
Inactive lac
repressor
Allolactose
(a) Lactose present, glucose scarce (cAMP level
high): abundant lac mRNA synthesized
Promoter
DNA
Operator
lacI
CAP-binding site
Inactive
CAP
lacZ
RNA
polymerase less
likely to bind
Inactive lac
repressor
(b) Lactose present, glucose present (cAMP level
low): little lac mRNA synthesized
Fig. 18-6
Signal
NUCLEUS
Chromatin
Chromatin modification
Levels of gene regulation in eukaryotes
DNA
Gene available
for transcription
Gene
Transcription
RNA
Exon
Primary transcript
Intron
RNA processing
Tail
Cap
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing
Active protein
Degradation
of protein
Transport to cellular
destination
Cellular function
Fig. 18-6
Signal
NUCLEUS
Chromatin
Chromatin modification
Levels of gene regulation in eukaryotes
DNA
Gene available
for transcription
Gene
Transcription
- Trancriptional activation in
eukaryotes
RNA
Exon
Primary transcript
Intron
RNA processing
Tail
Cap
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing
Active protein
Degradation
of protein
Transport to cellular
destination
Cellular function
Fig. 18-8-1
A Eukaryotic Gene
Enhancer
(distal control elements)
Poly-A signal
sequence
Proximal
control elements
Termination
region
Exon
Intron
Exon
Intron
Exon
DNA
Upstream
Promoter
Downstream
Fig. 18-9-1
Activators
Promoter
DNA
Enhancer
Distal control
element
TATA
box
Gene
Fig. 18-9-2
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA
box
General
transcription
factors
DNA-bending
protein
Group of
mediator proteins
Fig. 18-9-3
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA
box
General
transcription
factors
DNA-bending
protein
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
Transcription
initiation complex
RNA synthesis
Fig. 18-10
Enhancer
Control
elements
Promoter
Albumin gene
Crystallin gene
LIVER CELL
NUCLEUS
LENS CELL
NUCLEUS
Available
activators
Available
activators
Albumin gene
not expressed
Albumin gene
expressed
Crystallin gene
not expressed
(a) Liver cell
Crystallin gene
expressed
(b) Lens cell
Fig. 18-6
Signal
NUCLEUS
Chromatin
Chromatin modification
Levels of gene regulation in eukaryotes
DNA
Gene available
for transcription
Gene
Transcription
- Eukaryotes can control the
availability of DNA for
expression by altering the
extent of DNA packing
RNA
Exon
Primary transcript
Intron
RNA processing
Tail
Cap
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing
Active protein
Degradation
of protein
Transport to cellular
destination
Cellular function
Fig. 16-21a
Nucleosome
(10 nm in diameter)
DNA
helix
in diameter)
double
(2 nm
H1
Histones
DNA, the double helix
Histones
Histone tail
Nucleosomes, or “beads on
a string” (10-nm fiber)
Figure 18.7
Histone
tails
Amino acids
available
for chemical
modification
DNA
double
helix
Nucleosome
(end view)
(a) Histone tails protrude outward from a nucleosome
Acetylated histones
Unacetylated histones
(b) Acetylation of histone tails promotes loose chromatin
structure that permits transcription
Fig.
Fig.15-18
18-7
Paternal
chromosome
Normal Igf2 allele
is expressed
Maternal
chromosome
Normal Igf2 allele
is not expressed
(a) Homozygote
DNA
doubleIgf2
helix
Mutant
allele
inherited from mother
Histone
tails
Wild-type mouse
(normal size)
Amino
acids
available
for chemical
modification
Mutant Igf2 allele
inherited from father
(a) Histone tails protrude outward from a
nucleosome
Normal
size mouse
Dwarf mouse
(wild type)
Normal Igf2 allele
is expressed
Unacetylated histones
(mutant)
Mutant Igf2 allele
is expressed
Acetylated histones
Mutant Igf2 allele
Normal Igf2 allele
is
not
expressed
is not
expressed
(b) Acetylation of histone tails promotes
loose
chromatin structure that permits transcription
(b) Heterozygotes
Fig. 15-8
X chromosomes
Early embryo:
Two cell
populations
in adult cat:
Active X
Allele for
orange fur
Allele for
black fur
Cell division and
X chromosome
inactivation
Active X
Inactive X
Black fur
Orange fur
Fig. 18-6
Signal
NUCLEUS
Chromatin
Chromatin modification
Levels of gene regulation in eukaryotes
DNA
Gene available
for transcription
Gene
Transcription
-Alternative splicing can be
generated
RNA
Exon
Primary transcript
Intron
RNA processing
Tail
Cap
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing
Active protein
Degradation
of protein
Transport to cellular
destination
Cellular function
Fig. 18-11
Alternative splicing Exons
DNA
Troponin T gene
Primary
RNA
transcript
RNA splicing
mRNA
or
The DSCAM gene (Drosophila): ~38,000 possible splice variants
Fig. 18-6
Signal
NUCLEUS
Chromatin
Chromatin modification
Levels of gene regulation in eukaryotes
DNA
Gene available
for transcription
Gene
Transcription
- Proteins can be selectively
degraded
RNA
Exon
Primary transcript
Intron
RNA processing
Tail
Cap
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing
Active protein
Degradation
of protein
Transport to cellular
destination
Cellular function
Fig. 18-12
Ubiquitin ligase
Ubiquitin
Proteasome
Protein to
be degraded
Ubiquitinated
protein
Proteasome
and ubiquitin
to be recycled
Protein entering a
proteasome
Protein
fragments
(peptides)
Fig. 12-17b
Degraded
cyclin
G2
checkpoint
Cyclin is
degraded
MPF
Cdk
Cyclin
(b) Molecular mechanisms that help regulate the cell cycle
Cyclin accumulation
Cdk
Fig. 12-6d
Metaphase
Anaphase
Metaphase
plate
Spindle
Centrosome at
one spindle pole
Telophase and Cytokinesis
Cleavage
furrow
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Fig. 18-6
Signal
Levels of gene regulation in eukaryotes
NUCLEUS
Chromatin
Chromatin modification
Small, non-coding RNAs can
affect gene regulation at
multiple levels
DNA
Gene available
for transcription
Gene
Transcription
RNA
Exon
Primary transcript
Intron
RNA processing
Tail
Cap
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
mRNA in cytoplasm
Degradation
of mRNA
Translation
Polypeptide
Protein processing
Active protein
Degradation
of protein
Transport to cellular
destination
Cellular function
Nematodes with a GFP transgene
Nematodes with a GFP transgene
Treated with GFP dsRNA
dsRNA can reduce gene expression for generations
Fig. 18-13
Hairpin
miRNA
Hydrogen
bond
Dicer
miRNA
5 3
(a) Primary miRNA transcript
mRNA degraded
miRNAprotein
complex
Translation blocked
(b) Generation and function of miRNAs
Fig. 18-13
Hairpin
miRNA
Hydrogen
bond
Dicer
miRNA
5 3
(a) Primary miRNA transcript
mRNA degraded
miRNAprotein
complex
Translation blocked
(b) Generation and function of miRNAs
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