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GN 311 > Lecture 18 > Flashcards

Lecture 18 Flashcards

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1
Q

positive control

A
  • stimulation of transcription

- regulatory protein is activator

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2
Q

negative control

A
  • inhibition of transcription

- regulatory protein is repressor

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3
Q

structural genes

A

encode protein that are used in metabolism or biosynthesis or that play a structural role in the cell

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4
Q

constitutive or housekeeping genes

A

expressed continuously

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5
Q

regulatory genes

A

genes whose products, either RNA or proteins interact with other DNA sequences and affect the transcription or translation of those

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6
Q

regulatory elements

A
  • DNA sequences that are not transcribed but play a role in regulating genes and other DNA sequences.
  • affect the expression of sequences to which they are physically linked
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7
Q

domains

A

functional regions of 60-90 in DNA binding proteins with which there are characteristic motif structures

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8
Q

motif

A

characteristic structure that groups the DNA binding proteins

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9
Q

three motifs

A
  • helix-turn-helix
  • zinc fingers
  • leucine zipper
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10
Q

polycistronic

A

containing many bacterial genes that have a related function under the control of a single promotor

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11
Q

operon

A

a group of genes that are transcribed together along with additional sequences that control transcription

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12
Q

regulator gene

A
  • helps control transcription by the operon
  • not considered part of the operon
  • has its own promotor and produces a regulatory protein
  • regulatory protein binds to the operator and react with effectors
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13
Q

effectors

A

small molecules such as amino acids or sugars that are signals used by the cell to sense when a gene should be transcribed.

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14
Q

inducible operon

A
  • transcription normally off and needs to be turned on

- often in breakdown on precurose

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15
Q

repressible operon

A
  • transcription normally on and needs to be turned off

- usually control proteins that carry out biosynthesis of molecules needed in cells such as amino acids

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16
Q

negative inducible

A
  • regulatory genes encodes an active repressor that binds to the operator blocking transcription
  • inducer binds to repressor, alters shape of repressor, and prevents it from binding to mRNA.
  • transcription now turned on
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17
Q

allosteric

A

proteins which change shape when binding to another protein

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18
Q

negative repressible

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A
  • inactive repressor made

- corepressor must bind to repressor to stop transcription

19
Q

positive inducible

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A
  • inactive activator made

- inducer attaches to activator allowing transcription

20
Q

positive repressible

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A
  • active activator made

- repressor protein binds to block transcription

21
Q

lac operon background

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A
  • lactose cannot diffuse into E. Coli so must be transported by permease
  • must be broken down into glucose and galactose by beta-galactosidase - can also convert lactose to allolactose
  • negative inducible operon
  • lacZ encodes Beta-galactosidase
  • lacY encodes permease
  • lacA encdoes transacetylase
22
Q

when lactose is absent

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A
  • a few molecules of each protein are produced
23
Q

lactose present and glucose absent

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A
  • the rate of synthesis increases hugely
24
Q

coordinate induction

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A

the simultaneous synthesis of several proteins, stimulated by a specific molecule, the inducer

25
how the lac operon works
- allolactose (made by beta-galactosidase) acts as inducer - in absence of lactose, repressor is bound - in presence of lactose, some converted to allocates, which binds to the repressor and causes the repressor to be released
26
partial diploid
contains two copies of the lac operon
27
cis acting
able to control the expression of genes only on the same piece of DNA
28
trans acting
able to control expression of genes on other DNA molecules
29
lacI
- able to operate on either the plasmid or chromosomal copy of the operon - can transfer to either part of the diploid
30
lacI^s
- super repressor | - only deactivated by O^c
31
O^c
- repressor protein of any kind cannot bind | - only works on its gene though - cis acting
32
promotor mutations
- P- - interfere with binding of RNA polymerase to promotor so no Beta-galactosidase produced - cis-acting only
33
catabolite repression
- when glucose is available, genes that participate in the metabolism of other sugars are repressed - results from positive control
34
catabolism
break down molecules into smaller units and release energy
35
when glucose is low
high levels of cAMP binds to CAP which binds to promotor. RNA pol can now bind and transcription occurs
36
when glucose is high
no cAMP so CAP can't bind so RNA pol can't really bind and no transcription
37
trp operon overview
- negative repressible | - contains structural genes that help make tryptophan
38
tryptophan levels low
- RNA pol binds to the promotor and transcribes five structural genes into a single mRNA which is then translated.
39
tryptophan levels high
tryptophan binds to the repressor which activates it and now it binds to the operator so transcription turned off
40
attentuation
- transcription begins at the start site, but termination takes place prematurely, before the RNA polymerase even reaches the structural genes - premature termination of transcription also regulates the trp operon
41
attenuator
- base pairing of regions 3 and 4 with a string of uracil nucleotides - is a terminator - forms when tryptophan levels are high, causing transcription to be terminated before the trp structural genes can be transcribed
42
when tryptophan levels are high
- RNA pol transcribes DNA producing region 1 of 5' UTR - ribosome binds to 5' end of UTR and translates region 1 while region 2 transcribed - RNA pol transcribes region 3. ribosome doesn't stall at Trp codon - ribosome covers part of region 2, while region 4 and region 3 pair, producing attenuator
43
when tryptophan levels are low
- RNA pol transcribes DNA producing region 1 of 5' UTR - ribosome binds to 5' end of UTR and translates region 1 while region 2 transcribed - ribosome stalls at Trp codons in region 1 because tryptophan is low so it waits for it. region 2 not covered by ribosome when region 3 transcribed - region 3 transcribed and pairs with region 2, when region 4 transcribed, it cannot pair with region 3 because region 3 pairs with region 2. attenuator never forms and transcription continues
44
antiterminator
hairpin formed by region 2 and 3 without uracils

GN 311 (22 decks)

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