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Regulation
1. Overview of the various regulatory mechanisms observed in bacteria (figs 1 and 2
handout).
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Regulation at the level of gene structure (flagella phase variation, methylation of
DNA, degree of supercoiling).
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Control at the transcriptional level (sigma subunit, negative/positive regulatory
proteins).
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mRNA stability
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Control at the level of translation (translation initiation).
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Regulating the activity of a protein/enzyme (attenuation of translation, allosteric
enzymes, covalent modification).
Lectures will focus on regulatory mechanisms in which the central theme is that control is
mediated by low molecular substances which are either synthesized by the cell or present
in the environment. These low MW molecules, called EFFECTOR MOLECULES or
ligands, interact with specific protein molecules, called ALLOSTERIC PROTEINS, and
alter the properties of these proteins, i.e., maltose binding protein and MCP II.
2. Definition of constitutive, inducible, and repressible enzyme systems.
3. The Lactose Operon (an inducible enzyme system). Fig. 8.14
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Definition of an operon
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Diauxic growth: Fig. 8.18
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Graduitous inducers
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Operon regulated by a negative (lac repressor) and positive regulatory protein
(catabolite activator protein, CAP). Figs. 3 and 4
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Model to explain regulation at level of transcription.
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Catabolite repression and how explain. Fig 5
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How does the maltose operon differ from the lac operon?
4. Tryptophan Operon
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Feedback (end-product) inhibition of anthranilate synthetase (first enzyme
committed to tryp biosynthesis). Fig. 8.5
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Repression- tryp repressor. Fig. 8.13
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Attentuation: Fig. 8.25
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organization of tryp genes. Fig 6
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leader region (region between operator and first structual gene). Fig 6 and 7
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162 nucleotides with a transcriptional termination site at 3' end.
encodes for a short polypeptide chain (14 amino acid) which has two tryp codons.
base pairing that can occur within this region
impact that specific base pairing has on transcription
how translation effects transcription of tryp genes (model). State of translation
determine if tryp genes are transcribed.
5. Regulation of key enzymes in branched biosynthetic pathways. Fig 9
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sequential feedback inhibition.
isofunctional inhibition (isozymes).
concerted feedback inhibition.
cumulative feedback inhibition.
What is the difference between concerted and cumulative feedback inhibition.
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combined activation and inhibition.
6. Regulation of glutamine synthetase: an example of cumulative feedback inhibition and
covalent modification by adenylation. Fig 8 (Fig. 8.6 text)
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Glutamine synthetase (GS) composed of 12 identical subunits, each subunit
having 8 distinct allosteric sites (96 potential allosteric sites).
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To have cumulative feedback inhibition GS must be covalently modified by the
addition of an adenyl group (AMP from ATP) to each subunit. When fully adenylated,
GS is less active and more susceptable to cumulative feedback inhibition.
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Adenylating enzyme, AMP-adenyl transferase, also removes adenyl groups! How
does cell avoid futile recycling of ATP?
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Protein PII, a protein subject to covalent modification by uridyl transferase (UMP
from UTP). What controls if PII is modified or not? and how does this impact the
acitivity of GS?
7. Flagella phase variation. Fig 10
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ability to switch between making two types of flagellin proteins (subunit that
makes up filament component of flagellum).
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inversion of a region of DNA that contains promoter region for H2 flagellin gene
and H1 repressor.
revised 10/13/06