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genetics > chapter 12 part 1 > Flashcards

chapter 12 part 1 Flashcards

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Biology 101 flashcards
1
Q

constitutive (continuous) transcription

A

occurs for genes needed continuously to perform tasks (housekeeping genes) & are needed for the life of the cell

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2
Q

constitutive genes

A

actively expressed all the time

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3
Q

inducible genes

A

expressed only when their proteins are needed by the cell

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4
Q

regulated transcription (inducible)

A

needed in genes only needed for responses to changing environmental conditions or during certain phases of growth
-induces control of both initiation & amount of transcription

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5
Q

what is the major means of regulating gene expression in bacteria?

A

transcriptional regulation

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6
Q

what does transcriptional regulation control?

A

results from interactions between DNA-binding proteins & regulatory sequences of DNA

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7
Q

negative control of transcription

A

controls binding of a repressor proteins to a regulatory DNA sequence & preventing transcription
-bind to dna sequences called operators through a DNA-binding domain
-binding blocks transcription
-can be turned on or off by binding other components

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8
Q

positive control of transcription

A

involves binding of an activator protein to regulatory DNA & initiating gene transcription
-also have a dna-binding domain
-binding to dna causes rna polymerase to initiate transcription
-turned on or off

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9
Q

how many domains to acitvator/repressor proteins (TFs) have & what are they?

A

at least two
-dna binding domain & allosteric domain

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10
Q

what does the dna binding domain do?

A

it locates & binds operator dna sequence or other target dna sequences

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11
Q

what does the allosteric domain bind?

A

a molecule or protein, which causes a change in conformation of the dna-binding domain, altering its function
-turns dna binding on or off
-this is properly called allostery

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12
Q

what are the four categories of gene regulation

A

negative inducible, negative repressible, positive inducible, positive repressible

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13
Q

inducible

A

the effector molecule causes transcription to START

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14
Q

repressible

A

the effector molecule causes transcription to STOP

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15
Q

repressor

A

negative control

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16
Q

activator

A

positive control

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17
Q

all four catrgories of gene regulation require what?

A

allosteric effector/inducer/inhibitor/co-repressor molecule

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18
Q

negative inducible

A

-TF is a repressor
-binding of the effector molecule to the TF causes transcription to START
-effector molecule is an inducer
-lac operon in ex

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19
Q

negative repressible

A

-TF is a repressor
-binding of the effector molecule to the TF causes transcription to STOP
-effector molecule is a co-repressor
-trp operon is an ex

20
Q

positive inducible

A

-TF is an activator
-binding of the effector molecule to the TF causes transcription to START (co-activator)
-effector molecule is an inducer

21
Q

positive repressible

A

-TF is an activator
-binding of the effector molecule to the TF causes transcription to STOP
-effector molecule is an inhibitor

22
Q

what is the most common structural feature of homodimers in bateria?

A

the helix-turn-helix (HTH) motif, in which two alpha-helical regions interact with the DNA sequences

23
Q

what are the recognition & stabilizing helix separated by?

A

a turn in each polypeptide

24
Q

operons
-Genes in an operon nearly always participate in the same metabolic or biosynthetic pathway

A

clusters of genes undergoing coordinated transcriptional regulation by a shared regulatory region

25
Q

where are operons commonly found?

A

in bacterial genomes

26
Q

can operons be activated or repressed to control activity of a set of genes?

A

yes!
-switching mechanisms are typically responsive to environmental cues

27
Q

what operon of e. coli is responsible for producing three proteins needed for use of lactose

A

lactose (lac) operon

28
Q

what is the principle energy source for e.coli & most organisms?

A

glucose
-this monosaccharide is metabolized directly by the glycolysis pathway

29
Q

_________ is one of the many sugars that can serve as an alternate carbon source; its utilization is controlled by the lac operon, which is an inducible operon system

A

lactose
-inducible systems are turned on only when an inducer compound (lactose in this case) is available

30
Q

what is lactose made of?

A

glucose & galactose

31
Q

what bacteria phenotype can grow on media containing lactose as the only sugar?

A

lac +
-they do this by producing a gated channel (permease) at the cell membrane that allows lactose to enter the cell & the enzyme beta-galactosidase to break the beta-galactose linkage

32
Q

what does the breakdown of lactose also produce?

A

allolactose which acts as an inducer compound

33
Q

what does the lac operon consist of

A

multipart regulatory region & three structural genes

34
Q

how many binding sites does the regulatory region have?

A

-promoter (P) that binds to rna polymerase
-operator (O) (LacO) that binds the lac repressor protein
-the CAP binding site

35
Q

where are the regulatory regions located

A

immediately upstream of the start of transcription of the structural genes

36
Q

lac operon structural genes

A

-lacZ-encodes beta-galactosidase
(cleaves lactose into glucose & galactose)
-lacY- encodes a permease
(helps transport lactose into the cell
-LacA- encodes transacetylase
(dont know function)

37
Q

how are the lac operon structural genes transcribes?

A

as a single, polycistronic mRNA, which is translated to produce the three distinct polypeptides

38
Q

where is the lacl gene?

A

next to, but not part of, the lac operon

39
Q

lacl gene

A

constitutively expressed (made all the time)

40
Q

what does lacl encode?

A

lac repressor protein

41
Q

lac repressor protein

A

-is a homo-tetramer
-has a dna-binding domain that binds the the lacO sequence (operator)
-has an allosteric domain that binds the inducer- allolactose

42
Q

how does the lactose operator bind to the operator?

A

reversibly
-when allolactose is around, it can come off

43
Q

what does permease do

A

allows lactose into the cell, if permease gene is always off, we don’t let lactose in

44
Q

how would we make allolactose if we dont have a permease?

A

we never would make allolactose

45
Q

since there is a very low basal level of transcription from the operon, what does it make this system?
repressor stays on & every once in a while, it comes off randomly & the rna polymerase gets by… makes a low level basal transcription rate always

A

negative inducible control

46
Q

when lactose is + & glucose is -, what do we need to use as an energy source?

A

lactose
if lactose is around, we make allolactose which binds to the allosteric domain of the lac repressor

47
Q

what does the formation of the inducer-repressor complex alter?

A

the dna-binding domain of the repressor & prevents it binding the operator
-negative control (repression) is removed
-transcription of lac operon is induced

genetics (37 decks)

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