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GN 311 > Lec 26: Prokaryote regulation > Flashcards

Lec 26: Prokaryote regulation Flashcards

1
Q

Gene Regulation

A

the mechanisms and systems that control the expression of genes

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2
Q

structural genes

A

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

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3
Q

Regulatory Genes

A

are genes that encode products (RNA or Proteins),

-interact with other DNA sequence and affect the transcription and or translation of those sequences

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4
Q

Regulatory Elements

A

DNA sequences that are not transcribed, but play a role in regulating other nucleotide sequences (that they are linked to)

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5
Q

Helix-turn-Helix

A

DNA binding Protein MOtif

  • consists of two alpha helices connected by a turn
  • location: bacterial regulatory proteins, related motifs in eukaryotic proteins
  • binding site in DNA: major groove
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6
Q

Zink Fingers

A

DNA binding protein motif

  • -consists of a loop of amino acids containing a zinc ion
  • location: eukaryotic regulatory and other proteins
  • binding site in DNA: major groove
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7
Q

Leucine Zipper

A

DNA binding protein Motif

  • Helix of leucine residues and a basic arm, two leucine residue interdigitate
  • location: eukaryotic transcription factors
  • binding site in DNA-two adjacent major groves
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8
Q

Operon

A

a group of bacterial structural genes that are transcribed together (along with their promoter and additional sequences that control transcription)

  • regulates the expression of the structural genes by controlling transcription
  • usually mot important level of gene regulation
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9
Q

Regulator Proteins:

A

can bind to a region of the operon called the operator and affect whether transcription will take place

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10
Q

Characteristic os the regulation mechs. for transcirption

A

Rapid turn ON and rapid turn OFF
- provides the ability to respond rapidly to sudden changes

Sequential Gene Expression
-cascades of gene expression that turn on in order-these are cyclical

Constitutive Expression/Housekeeping Genes
-continuously expressed under normal conditions always ON such as tRNA and rRNA

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11
Q

Negative control

A

regulatory molecule is a repressor that binds to DNA and inhibits transcription

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12
Q

Positive Control

A

regulator molecule is a activator, binds to the DNA to stimulate Transcription

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13
Q

Inducible operon

A

transcription is normally off and is turned on when an inducer interacts with the repressor

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14
Q

Repressible Operon

A

transcription is normally on and is turned off when a corepressor interacts with repressor

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15
Q

Negative inducible

A
  • the regulator gene encodes an active repressor that readily binds to the operator, which blocks the RNA polymerase from binding to the promoter and prevents transcription
  • For transcription to take place, something must happen to prevent the binding of the repressor to the operator
  • SAID to be inducible because transcription is normally turned off and needs to be turned on/induced
  • Inducer binds to repressor and alters shape preventing it from bind to DNA-CALLED ALLOSTERIC PROTEIN
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16
Q

Negative Repressible

A
  • transcription normally takes place and must be turned off or repressed
  • the regulator protein is a repressor but is synthesized in a inactive form that cannot by itself bind to the operator
  • since there is no repressor bound to the operator RNA polymerase readily binds to the promoter and transcription of the structural genes take place
  • To turn off transcription, a COREPRESSOR binds to the repressor and makes it capable of binding to the operator
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17
Q

Positive inducible

A
  • Regulatory Protein=activator- it binds to the DNA (usually at a site other than the operator) and stimulates transcription
  • transcription takes place when an inducer has become attached to the regulator protein-making the regulator active
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18
Q

Positive Repressible

A
  • The regulatory protein is produced in a form that readily binds to DNA- meaning that transcription normally takes place and has to be repressed
  • Transcription is turned off when a substance becomes attachéd to the activator and makes unable to bind to the DNA
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19
Q

Lac Operon

A
  • basic unit for transcriptional control in bacteria
  • Lactose is broken down into galactose and glucose with the enzyme B-galactdisoe
  • Example of a negative inducible operon
20
Q

Operon

A

As a segment of DNA containing Control regions and structural genes, the structural regions are controlled by the controlling region

  • when lactose is absent from the medium few molecules of each protein is produced
  • if lactose is present and glucose is absent the rate of production increases
21
Q

structural gene

A

Z, Y, and A

-transcribed and translated into proteins

22
Q

LacZ

A

B-galactidose

23
Q

LacY

A

Permease

24
Q

LacA

A

transacetylase

25
Q

Inducer

A

Allolactose

26
Q

I

A
  • regulator gene-codes for the repressor, has two binding sites either binds to the allolactose or DNA
  • in the absence of lactose the repressor binds to the operator, thus RNA polymerase is blocked and NO TRANSCRIPTION
  • when lactose is present the repressor is inactivated by allolactose- RNA polymerase isn’t blocked and transcription is turned on
27
Q

P

A

promoter- binds RNA polymerase to allow transcription

28
Q

O

A

operator-interacts with repressor

29
Q

What is product during transcription?

A

polycistronic mRNA- which is translated into 3 different gene products

30
Q

Cis acting mutations of the lac operon

A

action of an element affects only the genes adjacent to it

EX: operator and promoter

31
Q

Trans acting mutations of the lac operon

A

Diffusible product is produced. The mutant gene does not have to be adjacent to the other genes to affect them
EX: repressor

32
Q

Structural gene mutations

A

Z-, Y-, A-

-results in defective enzymes

33
Q

Regulatory Gene mutations

A

mutations in LacI gene affect the production of both Z and Y because genes from both proteins are in the same operon and are regulated coordinately

34
Q

I-

A

mutation was constitutive, causing the lac proteins to be produced all the time whether lactose is present or not

  • repressor cannot bind to operator due to the repressors bad bind site
  • Lac I+ dominates over I- which brings normal regulation of protein production
35
Q

I+

A

trans acting

-dominates of I- which brings normal regulation of protein production

36
Q

I^s

A

prevents transcription form taking place even in the presence of lactose

  • produce defective repressors that could not be inactivated by an inducer (cannot bind to allolactose)
  • it dominates over I+
  • S=super repressor since it stays stuck to operator
37
Q

I^(-d)

A

had subunit of repressor are produced so that repressor cannot bind to operator
-Transdominant to I+

38
Q

Operator Mutation: O^c

A

constitutive operator- alters the sequence of DNA at the operator so that the repressor was no longer able to bind

  • Lac O^c is dominant over O+
  • cis acting

EX: I+O+Z+/I+OcZ-
-produced B-galactidose only in presence of lactose

39
Q

Promoter mutations: P-

A
  • promoter cannot bind to RNA Polymerase
  • dont produce the protein in either the presence or absence of lactose
  • cis acting
40
Q

cAMP

A

the presence of glucose inhibits

  • binding of cAMP-CAP complex is required for proper binding of RNA polymerase
  • NO glucose=cAMP present=active transcription
  • Positive control- activator (cAMP-CAP) binds to DNA to allow transcription at max level
41
Q

Tryptophan operon

A
  • makes tryptophan
  • negative control- regulating molecules bind to the DNA to turn genes off
  • Repressible system- repressor must interact with a corepressor (trp) and then the repressor-corepressor can bind to the DNA to turn off the operon
  • Alosteric aciton: a change occurs in the conformation of the repressor when it binds to TRP
42
Q

Constitutive mutants in TRP operon

A 
R-= inactive repressor- operon always on
Oc= operator cannot bind to repressor,always on
43
Q

TRP low levels present

A
  • repressor isn’t activated so doesn’t bind to the operator-transcription is ON
  • Regions 2 pairs with region 3, doesn’t terminate transcription (ANTITERMINATION)

MECH:

  • 2 trp codons in a row stall ribosome
  • Transcription gets ahead of ribosome
  • Allows regions 2 and 3 to pair which isn’t a termination signal
44
Q

High levels of TRP present

A
  • -decreases the production of the enzymes used to make TRP
  • repressor can bind to operator so NO Transcripton
  • Regions 3 pairs with region 4 which terminates transcription (ATTNENUATION)

MECH:

  • ribosome is just behind transcription
  • Ribosome blocks region 2
  • Regions 3 and 4 pair which is termination signal
45
Q

Yanofsky

A

Attenuation

  • premature termination of transcription
  • noticed that a deletion around 140-160 BP allowed an increase in transcription even when TRP is present
  • ATTENUATOR- located in the leader sequence and responsible for decreasing transcription when TRP is present
  • normally if TRP is present, some RNA polymerase escapes repressor complex and starts transcribing, but transcription ends after about 140 its. (in attenuator region)
46
Q

Antisense RNA

A

prokaryotic regulation at the translation level

-small RNA molecules complementary to parts of the mRNA base pair to mRNA and inhibit translation

47
Q

Riboswitches

A

Prokaryotic regulation at the translation level

  • are RNA sequence in the mRNA that affect the translation of that mRNA
  • REgulatory protein can be a end product from a biochemical reaction and can be regulating its ow production
  • REgulatory protein binds to the riboswitch area
  • Riboswitch forms a secondary structure that blocks the ribosome binding site thus preventing TRANSLATION

GN 311 (17 decks)

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