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GENE REGULATION
11.1 Proteins interacting with DNA turn
prokaryotic genes on or off in response to
environmental changes
• Early understanding of gene control
Figure 11.1A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Colorized SEM 7,000
– Came from studies of the bacterium
Escherichia coli
The lac Operon
• In prokaryotes, genes for related enzymes
– Are often controlled together in units
called operons
The Lac operon produces proteins
responsible for lactose utilization – so
the cell can use lactose
So if you were a cell, and lactose was
present, would you want these genes turned
ON or OFF?
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Regulatory proteins bind to control sequences
in the DNA and turn operons on or off in
response to environmental changes
Operon turned off (lactose absent)
Regulatory
gene
OPERON
Promoter Operator
Lactose-utilization genes
DNA
mRNA
Protein
RNA polymerase
cannot attach to
promoter
Active
repressor
Operon turned on (lactose inactivates repressor)
DNA
RNA polymerase
bound to promoter
mRNA
Protein
Lactose
Figure 11.1B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Inactive
repressor
Enzymes for lactose utilization
Other Kinds of Operons
• The trp operon
– Is similar to the lac operon, but functions
somewhat differently
Promoter
Operator
Genes
DNA
Active
repressor
Active
repressor
Tryptophan
Inactive
repressor
Inactive
repressor
Lactose
Figure 11.1C
lac operon
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
trp operon
EUKARYOTIC GENE EXPRESSION
11.2 Differentiation yields a variety of cell types,
each expressing a different combination of genes
• In multicellular eukaryotes
– Cells become specialized as a zygote
develops into a mature organism
Figure 11.2
Muscle cell
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Pancreas
cells
Blood cells
Overview of Gene Regulation in Eukaryotes
NUCLEUS
DNA Packaging
Chromosome
DNA unpacking
Other changes to DNA
Gene
Transcription Regulation
Gene
Transcription
Exon
RNA transcript
Intron
Addition of cap and tail
Tail
Splicing
mRNA in nucleus
Cap
Flow through
nuclear envelope
mRNA in cytoplasm
CYTOPLASM
Breakdown of mRNA
Translation
Brokendown
mRNA
Post-Transcriptional
Modification
- Splicing and other
additions
mRNA degredation
Polypeptide
Cleavage / modification /
activation
Active protein
Breakdown
of protein
Brokendown
protein
ure 11.9
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Post-Translational
Modification
-Cleavage, addition
of functional groups
11.4 DNA packing in eukaryotic
chromosomes helps regulate
gene expression
Wound around clusters of
histone proteins, forming a
string of beadlike nucleosomes
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
11.6 Complex assemblies of proteins control
eukaryotic transcription
Proteins involved in Transcription Control:
Transcription Factors – act at site of the promoter
Activators – bind to the enhancer region of DNA
Enhancers
Promoter
Gene
DNA
Activator
proteins
Transcription
factors
Other
proteins
RNA polymerase
Bending
of DNA
Figure 11.6
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Transcription
11.7 Eukaryotic RNA may be spliced in more
than one way
• After transcription, alternative splicing
– May generate two or more types of
mRNA from the same transcript
Exons
DNA
RNA
transcript
or
RNA splicing
Figure 11.7
mRNA
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
RNAi – RNA Interference
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
11.8 Translation and later stages of gene
expression are also subject to regulation
• Once in the Cytoplasm:
– mRNA breakdown
– Post-translational modification by cleavage, or
addition of functional groups like phosphate
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Protein Activation
– Polypeptides may require alteration to
become functional
Folding of polypeptide and
formation of S—S linkages
Cleavage
S S
Initial polypeptide
(inactive)
Folded polypeptide
(inactive)
Figure 11.8
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
S S
Active form
of insulin
Protein Breakdown
• Some of the proteins that trigger metabolic
changes in cells
– Are broken down within a few minutes or
hours
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
11.9 Review: Multiple mechanisms regulate gene
expression in eukaryotes
NUCLEUS
Chromosome
DNA unpacking
Other changes to DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of cap and tail
Tail
Splicing
mRNA in nucleus
Cap
Flow through
nuclear envelope
mRNA in cytoplasm
CYTOPLASM
Breakdown of mRNA
Translation
Brokendown
mRNA
Polypeptide
Cleavage / modification /
activation
Active protein
Breakdown
of protein
Figure 11.9
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Brokendown
protein