Download Chap 11 – Regulation of Eukaryotic Gene Expression

Chapter 11
How Genes Are Controlled
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Regulation of Eukaryotic Gene Expression
 Prokaryotes and eukaryotes employ regulatory
proteins that
– bind to specific segments of DNA and
– either promote or block the binding of RNA polymerase,
turning the transcription of genes on and off.
 In eukaryotes, activator proteins seem to be more
important than repressors. Thus, the default state for
most genes seems to be off.
 A typical plant or animal cell needs to turn on and
transcribe only a small percentage of its genes.
© 2012 Pearson Education, Inc.
Regulation of Eukaryotic Gene Expression
 Eukaryotes also need to regulate gene expression
during embryonic development
 Differentiation = cell specialization, in structure and
function
– is controlled by turning specific sets of genes on or off.
 Almost all of the cells in an organism contain an
identical genome.
 The differences between cell types are due to
selective gene expression.
© 2012 Pearson Education, Inc.
Figure 11.12
Root of
carrot plant
Single cell
Root cells cultured
in growth medium
Cell division
in culture
Plantlet
Adult plant
Figure 11.7
Chromosome
Chromosome
DNA unpacking
Other changes to the DNA
DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of a cap and tail
Splicing
Tail
Cap
mRNA in nucleus
Flow through
NUCLEUS nuclear envelope
CYTOPLASM
mRNA in cytoplasm
Breakdown of mRNA
Brokendown
mRNA
Translation
Polypeptide
Polypeptide
Cleavage, modification,
activation
Active
protein
Active protein
Breakdown
of protein
Amino
acids
DNA Packaging and Modification
 Eukaryotic chromosomes undergo multiple levels of folding
and coiling
– Nucleosomes are formed when DNA is wrapped around histone
proteins.
DNA double
– helix
Each
(2-nm diameter)
nucleosome bead includes DNA plus eight histones.
Metaphase
chromosome
Nucleosome
(10-nm diameter)
Tight helical
fiber (30-nm
diameter)
Linker
“Beads on
a string”
Histones
Supercoil
(300-nm diameter)
700 nm
DNA Packaging and chemical modifications can
affect gene expression
 DNA packing can prevent gene expression by preventing
RNA polymerase from contacting the DNA.
 More tightly compacted DNA - less likely DNA will be
transcribed
 Euchromatin - transcriptional active regions of DNA
 Heterochromation - transcriptional silent (highly
compacted)
Animation: DNA Packing
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DNA Packaging and chemical modifications can
affect gene expression
 Methylation of DNA
– Certain enzymes can add a methyl group to DNA bases,
without changing the sequence of the bases.
– Methylation generally inhibits gene expression
– Example: X-Chromosome inactivation
© 2012 Pearson Education, Inc.
DNA packaging and chemical modifications can
affect gene expression
 X-chromosome inactivation
– In female mammals, one of the two X chromosomes is
highly compacted and transcriptionally inactive.
– An inactivated X chromosome is called a Barr body.
© 2012 Pearson Education, Inc.
Figure 11.2B
Early Embryo
Adult
Two cell populations
X chromosomes
Allele for
orange fur
Cell division
and random
X chromosome Active X
inactivation Inactive X
Allele for
black fur
Inactive X
Active X
Orange
fur
Black fur
Figure 11.7
Chromosome
Chromosome
DNA unpacking
Other changes to the DNA
DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of a cap and tail
Splicing
Tail
Cap
mRNA in nucleus
Flow through
NUCLEUS nuclear envelope
CYTOPLASM
mRNA in cytoplasm
Breakdown of mRNA
Brokendown
mRNA
Translation
Polypeptide
Polypeptide
Cleavage, modification,
activation
Active
protein
Active protein
Breakdown
of protein
Amino
acids
Regulation of Transcription
 Eukaryotic RNA polymerase requires the assistance
of proteins called transcription factors.
 Transcription factors recruit RNA polymerase to
gene’s promoter
 Activator proteins, which bind to DNA sequences
called enhancers and help increase rate of gene
transcription.
 Silencers are repressor proteins that
– may bind to DNA sequences and
– inhibit transcription.
Animation: Initiation of Transcription
© 2012 Pearson Education, Inc.
Figure 11.3
Enhancers
Promoter
Gene
DNA
Activator
proteins
Transcription
factors
Other
proteins
RNA polymerase
Bending
of DNA
Transcription
Figure 11.7
Chromosome
Chromosome
DNA unpacking
Other changes to the DNA
DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of a cap and tail
Splicing
Tail
Cap
mRNA in nucleus
Flow through
NUCLEUS nuclear envelope
CYTOPLASM
mRNA in cytoplasm
Breakdown of mRNA
Brokendown
mRNA
Translation
Polypeptide
Polypeptide
Cleavage, modification,
activation
Active
protein
Active protein
Breakdown
of protein
Amino
acids
Regulation of mRNA Processing
 Alternative RNA splicing
Animation: RNA Processing
– produces different mRNAs from the same transcript,
– results in the production of more than one polypeptide from the same
gene
Exons
1
DNA
2
4
3
Introns
RNA
transcript
5
Introns
Tail
Cap
1
2
5
4
3
RNA splicing
or
mRNA
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1
2 3
5
1
2 4
5
Figure 11.7
Chromosome
Chromosome
DNA unpacking
Other changes to the DNA
DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of a cap and tail
Splicing
Tail
Cap
mRNA in nucleus
Flow through
NUCLEUS nuclear envelope
CYTOPLASM
mRNA in cytoplasm
Breakdown of mRNA
Brokendown
mRNA
Translation
Polypeptide
Polypeptide
Cleavage, modification,
activation
Active
protein
Active protein
Breakdown
of protein
Amino
acids
11.6 Later stages of gene expression are also
subject to regulation
 After mRNA is fully processed and transported to
the cytoplasm, gene expression can still be
regulated by
– breakdown of mRNA,
– initiation of translation,
Animation: Blocking Translation
Animation: mRNA Degradation
– protein activation, and
Animation: Protein Degradation
– protein breakdown.
Animation: Protein Processing
© 2012 Pearson Education, Inc.
Figure 11.7
Chromosome
Chromosome
DNA unpacking
Other changes to the DNA
DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of a cap and tail
Splicing
Tail
Cap
mRNA in nucleus
Flow through
NUCLEUS nuclear envelope
CYTOPLASM
mRNA in cytoplasm
Breakdown of mRNA
Brokendown
mRNA
Translation
Polypeptide
Polypeptide
Cleavage, modification,
activation
Active
protein
Active protein
Breakdown
of protein
Amino
acids
Figure 11.6
Folding of the polypeptide
and the formation of
S—S linkages
Cleavage
S S
Initial polypeptide
(inactive)
Folded polypeptide
(inactive)
S S
Active form
of insulin
11.7 Review: Multiple mechanisms regulate gene
expression in eukaryotes
 These controls points include:
1. chromosome changes and DNA unpacking,
2. control of transcription,
3. control of RNA processing including the
– addition of a cap and tail and
– splicing,
4. flow through the nuclear envelope,
5. breakdown of mRNA,
© 2012 Pearson Education, Inc.
11.7 Review: Multiple mechanisms regulate gene
expression in eukaryotes
6. control of translation, and
7. control after translation including
– cleavage/modification/activation of proteins and
– breakdown of protein.
© 2012 Pearson Education, Inc.