Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 13
Gene Regulation
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Gene regulation in bacteria and
eukaryotes
• Bacterial cells
–Grow rapidly and have short life span
–Transcriptional-level control best
• Eukaryote cells
–Long life span
–Gene regulation complex
–Transcriptional-level control dominates, but
other levels important, also
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Gene regulation in bacteria
• Most organized into operons
–Gene complex plus linked DNA
–Each has single promoter region upstream
• Operator regulates transcriptional-level
control of operon
–When repressor protein binds to operator,
it prevents transcription
–Binds specifically to the lac operator
sequence
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Biology, Seventh Edition
CHAPTER 13 Gene Regulation
The lac
operon
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Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Genetic and biochemical characterization
of the lac operon
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Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Inducible, repressible, and
constitutive genes
• Inducible operon, such as lac operon,
normally turned off
• Repressible operon, such as the trp
operon, normally turned on
• Constitutive genes
–Neither inducible nor repressible
–Active at all times
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
The trp operon
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Negative regulators inhibit
transcription
• Repressible and inducible operons
• When repressor protein binds to the
operator, transcription is turned off
• Positive regulators stimulate
transcription
• Some inducible operons
• Regulated by activator proteins
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Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Positive
control of
the lac
operon
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
A regulon
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Gene regulation in eukaryotic
cells
• Not organized into operons
• Gene regulation occurs at the levels of
–Transcription
–mRNA processing
–Translation
–The protein product
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Eukaryotic promoters vary in
efficiency, depending on UPEs
• Promoter consists of
–RNA polymerase-binding site
–Upstream promoter elements (UPEs)
• Number and types of UPEs
determine efficiency
• Inducible eukaryotic genes
controlled by enhancers
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Regulation
of transcription
in eukaryotes
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Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Regulatory proteins
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Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Stimulation
of
transcription
by
an enhancer
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Chromosome organization may
affect gene expression
• Genes are inactivated by changes in
chromosome structure
• DNA methylation is mechanism that
perpetuates gene inactivation
• Multiple copies of some genes present in
one chromosome
• Gene amplification
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
• Differential mRNA processing
• Cells in each tissue produce own version
of mRNA
• For example, different forms of troponin,
a protein that regulates muscle
contraction, produced in different muscle
tissue
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 13 Gene Regulation
Differential mRNA processing
Copyright © 2005 Brooks/Cole — Thomson Learning