Gene regulation:

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Lecture 37

• Gene regulation
• Control of gene expression.
• (Prokaryotic cells)

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Regulation of Gene Expression.
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Regulation depends on the type of metabolism.
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Turn-on a Catabolic Pathway.
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Turn-off a Anabolic Pathway.
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Transcription is regulated by binding of a
REGULATOR to a OPERATOR.
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Gene regulation in prokaryotes 1. By positive
control a. with induction of gene expression b.
with repression of gene expression 2. By negative
control a. with induction of gene expression b.
with repression of gene expression.
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REGULATORS are DNA-binding, Allosteric proteins.
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(Prokaryotic) Operon.
Structural genes
P
O
A
B
C
R
DNA
RNA
active regulator
protein
E1
E2
E3
inactive regulator
Function
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Example 1 Regulation of the Tryptophan Operon by
availability of tryptophan.
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Tryptophan operon
Without tryptophan
polymerase
Structural genes
P
O
Z
Y
A
R
inactive repressor
Function
With tryptophan
P
O
Z
Y
A
R
active repressor
Tryptophan
inactive repressor
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Example 1 Regulation of the Lactose Operon by
availability of lactose.
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Lactose operon
Without lactose
P
O
Z
Y
A
R
active repressor
polymerase
With lactose
Structural genes
P
O
Z
Y
A
R
inactive repressor
active repressor
Function
Lactose
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(Prokaryotic) Operon.
Structural genes
P
O
A
B
C
R
DNA
RNA
active regulator
protein
E1
E2
E3
inactive regulator
Function
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Gene regulation in prokaryotes 1. By positive
control a. with induction of gene expression b.
with repression of gene expression 2. By negative
control a. with induction of gene expression b.
with repression of gene expression.
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Tryptophan operon
Without tryptophan
polymerase
Structural genes
P
O
Z
Y
A
R
inactive regulator
Function
With tryptophan
P
O
Z
Y
A
R
active repressor
Tryptophan
inactive regulator
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Lactose operon
Without lactose
P
O
Z
Y
A
R
active regulator
polymerase
With lactose
Structural genes
P
O
Z
Y
A
R
inactive repressor
active regulator
Function
Lactose
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Example 3 Lactose Operon. Breakdown of lactose
more difficult than breakdown of glucose
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Example 3 Lactose Operon. Lactose Regulator and
CAP Regulator.
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cAMP structure.
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Example 3 Lactose Operon has two Operators
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Example 3 Lactose Operon. Lactose Regulator and
CAP Regulator Negative control and
Positive control with induction.
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Example 3 Lactose Operon. Lactose Regulator and
CAP Regulator Negative control and
Positive control with induction.
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Fig. 14-6, p. 312
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Example 3 Lactose Operon.
GLU LAC Transcription
NO NO
Yes NO
NO YES
YES YES
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Glucose low, cAMP high promotor activated
Glucose high, cAMP low, promotor not activated
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Glucose low Lactose not present
Glucose low Lactose present
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Prokaryotic Regulator - Operator Transcription
Factor - Response Element.
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Transcription Factors have a DNA-Binding Domain.
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Prokaryotic Regulator - Operator Transcription
Factor - Response Element.
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Transcription Factors have a DNA-Binding Domain.
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Three DNA-Binding Domains Helix-turn-Helix.
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Three DNA-Binding Domains Zinc-finger.
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Zinc finger.
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Transcription Factor with 3 Zn-finger domains
bound to DNA.
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Three DNA-Binding Domains Leucine zipper.
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(Helix-turn-helix)
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Lecture 38

• Gene regulation
• Eukaryotic cells,
• Transcription factors.

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Regulation of gene expression eukaryotes
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Organization of Eukaryotic Gene
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Regulation of gene transcription activation of a
TF by phosphorylation..
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Regulation of gene transcription activation of a
TF by removal of inhibitor..
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Eu-chromatin and Hetero-chromatin
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Common Bases
Methylated bases
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