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BIOL 202 > Lecture 25 > Flashcards

Lecture 25 Flashcards

1
Q

when are tissue/cell/time-specific genes controlled?

A

controlled at level of transcription

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2
Q

5 unique features of prokaryotic cells

A
  1. no nucleus –> transcription + translation occur simultaneously
  2. 1 circular chromosome
  3. fewer proteins associated with DNA
  4. no introns –> no splicing
  5. genes for 1 metabolic process organized in operon
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3
Q

what is a major point of gene regulation in prokaryotic cells?

A

transcription initiation

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4
Q

organization of a gene (5)

A
  1. promoter
  2. -35/-10 consensus sequence
  3. +1 nt = TSS
  4. ATG (Met)
  5. gene
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5
Q

what is the role of -35/-10 consensus sequence?

A

binding site for RNA pol

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6
Q

how is RNA pol recruited to -35/-10 promoter sequences?

A

sigma factor subunit of RNA pol scans DNA and binds the -35/-10 promoter sequences –> recruits + properly positions the rest of RNA pol at TSS

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7
Q

Describe the default state of prokaryotic gene

A

ON

sigma factor easily binds promoter since prokaryotic DNA is more simple and not wound in histones

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8
Q

positive regulation

A

activator binds activator-binding site upstream of promoter to allow RNA pol to bind and allow transcription

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9
Q

what happens when the activator is not bound to the activator-binding site?

A

there is low transcription

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10
Q

negative regulation

A

repressor binds operator downstream of promoter to block RNA pol and block transcription

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11
Q

what happens when the repressor is not bound to the operator?

A

RNA pol can bind promoter so transcription can occur

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12
Q

describe allosteric regulation on activator

A

effector binds activator –> activator changes conformation so it can bind DNA and activate transcription (gene ON)

no effector –> activator cannot bind DNA or activate transcription (gene OFF)

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13
Q

describe allosteric regulation on repressor

A

effector binds repressor –> repressor changes conformation so it cannot bind operator and stops repressing (gene ON)

no effector –> repressor binds operator and represses activation (gene OFF)

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14
Q

What is an inducer?

A

an effector that increases gene expression

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15
Q

what organism is the Lac operon found in?

A

E. coli

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16
Q

why must the lac operon be regulated?

A

energetically costly to produce mRNA and proteins –> better to only be active when lactose is available

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17
Q

2 enzymes involved in lac operon

A
  1. LacY –> PERMEASE
  2. LacZ –> beta-GALACTOSIDASE
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18
Q

organization of lac operon

A

REGULATORY COMPONENTS:
- repressor protein (not in operon)
- promoter
- operator

STRUCTURAL GENES (PROTEINS):
- LacZ
- LacY

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19
Q

3 characteristics of lac operon

A
  1. inducible
  2. under negative control
  3. under positive control
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20
Q

lac operon when there is NO LACTOSE

A

repressor protein is produced and binds operator –> RNA pol is blocked –> no transcription

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21
Q

lac operon when there IS LACTOSE

A

repressor protein is produced but lactose is effector that prevents it from binding operator –> RNA pol is active –> LacZ and LacY transcribed on 1 mRNA

22
Q

when is I expressed?

A

I = repressor protein

always expressed!! independent of lactose

23
Q

synthetic inducer of lac operon

A

IPTG

24
Q

3 main classes of mutations

A
  1. structural gene mutants
  2. uninducible mutants
  3. constitutive mutants
25
Q

what are structural gene mutations?

A

affect function of 1 enzyme, the other is inducible

26
Q

describe the production of beta-galactosidase and permease with Z+Y+ genotype (absence vs presence of lactose)

A

beta-galactosidase:
- no lactose = no activity
- lactose = activity

permease:
- no lactose = no activity
- lactose = activity

this is WT

27
Q

describe the production of beta-galactosidase and permease with Z-Y+ genotype (absence vs presence of lactose)

significance of these results?

A

beta-galactosidase:
- no lactose = no activity
- lactose = no activity (UNINDUCIBLE)

permease:
- no lactose = no activity
- lactose = activity (INDUCIBLE)

since both enzymes are in 1 operon, transcription can occur normally but someting directly affecting beta-galactosidase only

28
Q

what are uninducible mutants?

A

can’t make LacZ AND LacY in presence of IPTG –> failure of activation

29
Q

what are constitutive mutants?

A

make both LacZ and LacY even in absence of IPTG –> failure of repression

30
Q

what is a partial diploid?

A

prokaryote is haploid for everything except diploid for lac operon

31
Q

2 things that a partial diploid lets you test

A
  1. dominant vs recessive
  2. cis vs trans-acting factors
32
Q

what is a cis-acting factor?

A

mutation only affects transcription of genes on same DNA molecule –> mutation in REGULATORY element

33
Q

what is a trans-acting factor?

A

mutation also affects transcription of genes on the other DNA molecule –> mutation affects coding of DIFFUSIBLE PROTEIN

34
Q

what do P mutations affect? how do we know?

A

haploid E. coli with mutant P makes LacY and LacZ uninducible –> failure of activation

35
Q

do P mutations act in cis or trans? how do we know?

A

P mutations affect transcription of genes on the same DNA molecule –> cis

P-Z+Y+ / P+Z-Y- makes LacY and LacZ uninducible, since acting in cis the WT P cannot compensate for P-

36
Q

what do O mutations affect? how do we know?

A

haploid E. coli with mutant O makes LacY and LacZ constitutively active –> failure of repression

37
Q

do O mutations act in cis or trans? how do we know?

A

O mutations affect transcription on the same DNA molecule –> cis

O+Z+Y+/OcZ-Y- makes LacY and LacZ inducible only, since acting in cis the Oc cannot cause constitutive activity bc Z and Y are mutant

38
Q

what does it mean when O is constitutive?

A

repressor never bound so enzymes can be activated

39
Q

what are the 2 elements of the lac operon that are cis-acting?

A

promoter and operator

40
Q

what is the effect of the I mutation?

A

haploid E. coli with mutant I makes LacY and LacZ constitutively active –> failure of repression

41
Q

do I mutations act in cis or trans? how do we know?

A

I mutation affects both DNA molecules –> trans

I+Z-Y- / I-Z+Y+ makes LacY and LacZ inducible, since acting in trans the WT repressor can bind both DNA molecules

42
Q

what is the Is mutation?

A

super-repressor mutation –> operon becomes uninducible

43
Q

what happens if the genotype is IsZ+Y+ / I+Z+Y+?

A

I+ cannot complement for Is so Is on any DNA molecule makes all systems uninducible

44
Q

relationship of Is to I+

A

Is is dominant to I+

45
Q

how does Is block transcription?

A

mutation affects allosteric site so inducer cannot bind and repressor stays bound to DNA to block transcription

46
Q

what allows for positive regulation of the lac operon?

A

glucose

47
Q

if glucose and lactose are present, which will E. coli prefer to use?

A

glucose

48
Q

how does glucose allow for positive regulation

A

increased glucose = decreased cAMP

decreased cAMP = CAP can’t bind DNA

CAP can’t bind DNA = no transcription activation

49
Q

what is the role of CAP

A

Binds DNA to allow RNA pol to bind promoter

50
Q

what happens to the lac operon if:
- glucose is present / low cAMP
- no lactose

A

glucose is present = CAP can’t activate transcription

no lactose = repressor binds operator so no transcription

REPRESSION

51
Q

what happens to the lac operon if:
- glucose is present / low cAMP
- lactose is present

A

glucose is present = CAP can’t activate transcription

lactose = prevents repressor from binding operator so there’s some basal transcription

NO REPRESSION
NO ACTIVATION

52
Q

what happens to the lac operon if:
- no glucose / high cAMP
- lactose is present

A

no glucose = CAP can activate transcription

lactose = prevents repressor from binding operator

ACTIVATION

BIOL 202 (29 decks)

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