regulation of prokaryotic gene expression Flashcards

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1
Q

what are housekeeping genes

A

genes that are always switched on
(genes that produce proteins involved in making amino acids, transcription, translation etc)

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2
Q

most regulation of gene expression in bacteria is:

A

transcriptional control - no mRNA synthesis

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3
Q

negative control of transcription

A

binding of a repressor protein to a regulatory DNA sequence preventing transcription of a gene

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4
Q

positive control of transcription

A

binding of an activator protein to a regulatory DNA sequence, inititiates transcription

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5
Q

what is an operon

A

cluster of bacterial genes undergoing transcriptional regulation
-genes in an operon participate in the same metabolic/biosynthetic pathway

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6
Q

how is lac operon an inducible operon system

A

turned on only when inducer compound is available = lactose

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7
Q

lac operon - what is the structural gene region -

A

has 3 protein coding genes - lacZ, lacY, lacA

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8
Q

lac operon - what is the regulatory region -

A

-CAP binding site
-promoter that binds RNA polymerase
-operator that binds lac repressor protein

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9
Q

structural gene region - what do the 3 genes encode

A
  1. lac Z - encodes B galactosidase, cleaves bond between lactose to form galactose and glucose
  2. lac Y - encodes lactose permease - uptake of lactose from the environment
  3. lac A - encodes transacetylase

3 genes transcribed as mRNA, then translated to 3 polypeptides

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10
Q

lacl gene produces the ……….. protein next to the lac operon

A

lac repressor protein that then binds to the operator of lac operon and allolactose binds to it (inducer)

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11
Q

breakdown of lactose produces small amount of ….. - inducer compound. slightly modified version of lactose

A

allolactose

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12
Q

when there’s no lactose present - lac operon expressed at very low levels
what happens

A

lac repressor protein binds to operator (lacO) sequence inhibiting transcription

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13
Q

when there’s lactose present - lac operon expressed - transcription
what happens

A

B-galactosidase produces allolactose which binds to lac repressor forming inducer-repressor complex
-repressor protein is now inactive because it is bound to allolactose so can’t bind to the operator
-RNA polymerase binds to promotor and carries out transcription

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14
Q

when there’s lactose present (no glucose) - cAMP is high or low

A

high cAMP binds to CAP
CAP-CAMP then binds to the lac promoter region stimulating a high level of transcription

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15
Q

when there’s no lactose present (glucose) - cAMP is high or low

A

low cAMP - prevents transcription

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16
Q

mutation in lacl gene -

A

mutant lac repressor protein can’t bind to operator region
-lac operon consitutively expressed - B-galactosidase always present

17
Q

mutation in operator region (lacO) -

A

lac repressor protein can’t bind to mutated operator sequence
-lac operon constitutively expressed - B galactosidase always present

18
Q

mutation in laclS (super lac repressor)

A

mutant repressor protein cannot bind to allactose
-so binds to operator constitutively
-SO transcription never happens even when there’s lactose

19
Q

arabinose released in intestine after plant is eaten but not absorbed by intestine - it is a

A

carbon source for gut E.coli if glucose is absent

20
Q

E.coli arabinose operon - contains

A

genes required for metabolism of arabinose

21
Q

ara operon has a …. regulatory protein (araC) that carries out both positive and negative transcriptional regulation

A

single

22
Q

arabinose operon - what happens when there’s no arabinose

A

araC protein monomers bind to araI and araO2, monomers link to one another forming DNA loop
-DNA loop stops RNA polymerase and CAMP-CAP binding to promoter, so ara operon is not expressed

23
Q

arabinose operon - what happens when there is arabinose

A

arabinose breaks the connection between araC proteins at araI and araO2
-opens up DNA loop
-2nd araC-arabinose complex binds to araI and interacts with RNA pol
-CAP-CAMP binds CAP binding site - RNA pol binds to promotor and initiates transcription

24
Q

correct order of steps that can be used to identify a gene whose mutation causes a genetic disorder

A

map the mutation to the arm of a chromosome, fine map the position of the mutation using other known genetic markers on that arm, identify candidate genes, use DNA sequencing to determine mutations

25
Q

how often do E.coli replicate under optimal growing conditions

A

every 20 minutes

26
Q

genetic exchange in bacteria can be mediated by bacteriophage. what is this type of horizontal gene transfer called

A

transduction

27
Q

where does lac repressor bind

A

the operator lacO is found in the regulatory region and is where the lac repressor protein binds

28
Q

what does lacA encode

A

transacetylase

29
Q

what does lacZ encode

A

B-galactosidase

30
Q

what does lacY encode

A

lactose permease - uptake of lactose from the environment