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Regulation of gene expression
Bio119
I. Why regulate enzymes?
A. An organism doesn’t need to make each protein encoded by every
gene on the chromosome.
B. The organism only needs a subset of these proteins, which will
depend on the condition.
C. Even a subset of these proteins need not be synthesized in the same
amounts.
D. Adaptation to specific environmental conditions can be
accomplished by altering the levels of mRNA available for
translation.
E. Based on energetics, controlling transcription prevents unnecessary
usage of nucleotide triphosphates (dNTP) and costly protein synthesis.
F. Regulation of metabolism can occur by:
II. Regulation of transcription (induction and repression):
A. Some enzymes are always made at the same levels.
1. This is called: __________________ expression
2. The enzyme is always present regardless of nutrients
available to the organism.
3. The control of mRNA levels is governed by:
B. However, many genes are transcriptionally regulated.
1. This occurs when other proteins control:
2. These proteins respond to signals from the environment of
the bacterial cell
3. Enzyme induction can occur when the presence of a
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substrate results in an enzyme being synthesized.
4. Control of enzyme induction can occur in two ways:
III.
Negative Regulation
A. Often carried out by: ________________
1. Repressors proteins __________ with the transcription of
genes.
2. Environmental signals can usually ___________ repression.
B. Repressors bind to ______________ sites in the promoter
sequence.
1. Usually located:
2. When the repressor binds:
3. When repressor is not bound:
C. Lactose usage by the lac operon (Figure 13.12)
1. Lactose catabolism is induced when:
2. ________ represses lac operon in the absence of:
3. Adding lactose causes:
4. This is mediated by a metabolite called:
D. Tryptophan biosynthesis is also negatively regulated but in a
different way than the lac operon.
1. Tryptophan biosynthesis is induced:
2. Tryptophan biosynthesis is repressed when:
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3. This occurs because:
4. Binding of ________ causes _________of trp transcription.
5.
6.
7. Once enough tryptophan is made:
IV.
Positive regulation
A. Often is carried out by activators
1. Protein that _______________ transcription in response to
environmental signal.
B. These regulators also bind to specific operator sites:
1. Operator positions are usually upstream of the -35 element.
2. Some can be 100’s of bases upstream for promoter. These
require:
3. Many Sigma 70 dependent promoters have well conserved:
4. An activator protein often helps:
C. Maltose regulon, genes controlled by MalT regulator and in
response to maltose and related sugars. (Fig 13.14)
1. The regulon contains four different operons involved in
uptake and metabolism of maltose and related sugars
2. MalT is usually inactive when it is made (MalTi)
3. MalT is activated when it binds _______________(MalTa)
4. MalT dependent promoters:
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5. MalT promoters also have:
6. When MalTa binds:
V. Global regulation (CCR example)
A. This occurs when one regulator controls transcription of a large
subset of genes and operons.
B. An example is carbon catabolism.
1. Also called carbon catabolite repression (CCR)
C. Glucose vs. other catabolites
1. Catabolites are:
2. E. coli will use glucose first because:
3. Lactose, maltose, and other catabolites require more energy
input for breakdown into monomers.
D. Gene regulation of catabolite operons and genes is mediated the
CRP (cAMP receptor protein) regulator (book calls it CAP, catabolite
activator protein).
E. CRP activation:
1.
2. Can function as both a repressor and activator depending on:
F. How does the bacterium make cAMP?
1. From an adenylate cyclase:
2. Adenlylate cyclase is activated when:
3. cAMP levels are high during:
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G. When glucose is present things are different:
1.
2.
VI.
H. How many genes are in the E. coli CRP regulon?
1. CRP can bind to ~200 promoters
2. This leads to the consequence of controlling >50% of the
transcriptional units (genes and operons) in E. coli.
Aerobic/Anaerobic regulation:
A. ArcAB, two component sensor and response regulator
1. ArcB:
2. ArcA:
3. ArcA-P control induces/repress aerobic metabolism.
B. FNR, senses oxygen directly with an iron sulfur cluster
1. Aerobic conditions:
2. Anaerobic conditions:
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