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Mol. Gen. (GENE2000) > Gene regulation > Flashcards

Gene regulation Flashcards

1
Q

*Why is gene regulation important?

A

so that you don’t waste resources or energy synthesising proteins you don’t need at the moment

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2
Q

How does gene regulation help a bacterial cell quickly adapt?

A

gene regulation will switch genes on or off to adapt to the cond. of the surroundings (ie. reduce or increase synthesis of proteins in response to the cond.= survive)

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3
Q

How does gene regulation help cells in a human to specialise?

A

gene regulation controls which genes are to be switched on in a cell for it to function properly w/ other cells in the tissue (= so organ functions properly)

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4
Q

Explain why in some situations it may be more correct to talk about genes being “turned up” or “turned down” rather than “turned on or off”.

A

“turned up or down” is correct because it means expression of genes are up-/down-regulated. Genes aren’t really “turned off”, bc they can still be transcribed (& translated?) but inefficiently

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5
Q

What is chromatin remodeling?

A
  • localised loosening of DNA around histone core

=> access DNA for transcription

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6
Q

What is an operon?

A

many genes in a section of DNA (in b/w a promoter & terminator) => transcribed to give polycystronic mRNA

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7
Q

Explain what is meant by “an inducible gene”.

A

Genes normally switched OFF but can be switched on by an INDUCER

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8
Q

Explain what is meant by “a repressible gene”

A

Genes normally switched ON but can be switched off by a REPRESSOR

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9
Q

Explain what is meant by “a constitutive gene”.

A

Genes that are ALWAYS ON (not regulated)

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10
Q

In gene regulation, explain what is meant by “positive control”.

A

Gene expression controlled by an ACTIVATOR

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11
Q

In gene regulation, explain what is meant by “negative control”.

A

Gene expression controlled by a REPRESSOR

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12
Q

What is a promoter? Is this cis acting or trans acting?

A

Region w/in DNA that is upstream of a gene. Types: Core & Regulatory promoter
- cis acting

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13
Q

What is an enhancer? Is this cis acting or trans acting?

A

(cis acting) DNA sequences w/in, up- / down-stream from gene & interact w/ multiple regulatory proteins & activator proteins (=> alter rate of transcription). It is specific for the PROMOTER

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14
Q

What are transcription factor? Are they cis acting or trans acting?

A

(trans-acting) bind to regulatory region = control transcription of genes

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15
Q

Explain how high levels of tryptophan (trp) in a cell can cause decreased expression of the operon. (through 2 lvls of control)

A
  1. Allosterically activated repressor: inducer (trp) binds to repressor => allosteric shift = can bind to operator = blocks pathway for transcription
  2. Attenuation: trp-charged tRNA available => ribosome moves @ quicker rate = prevent 2:3 stem-loop from forming, but 3:4 loop forms pulling mRNA out of RNA pol = transcription terminated
    * =>both methods aim to stop synthesis of enzymes which make trp (bc Hi [trp])
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16
Q

Explain how low levels of tryptophan (trp) in a cell can cause increase expression of the operon. (through 2 lvls of control)

A
  1. Allosterically activated repressor: repressor protein can’t bind to operator = RNA pol binds to promoter => transcription
  2. Attenuation: trp-charged tRNA scarce => ribosome moves @ slower rate = 2:3 stem-loop forms = transcription continues
    * =>both methods aim to synthesise enzymes which make trp (bc Lo [trp])
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17
Q

Explain the effect of Hi Lactose levels on the lac operon expression.

A
  1. repressor protein expressed
  2. lactose (inducer) binds to repressor => allosteric shift
  3. repressor can’t bins to operator => RNA pol binds => transcription => translation
  4. => Enzymes convert lactose into galactose & glucose
18
Q

Explain the effect of Low Lactose levels on the lac operon expression.

A
  1. repressor protein expressed
  2. binds to operator
  3. RNA binds to promoter but can’t transcribe bc blocked by repressor
  4. ≠ no enzymes
19
Q

Explain the effect of High Glucose levels on the lac operon expression.

A
  1. Glucose = decreases cAMP lvls
  2. cAMP - Catabolite-activitaing protein (CAP) complex can’t form
  3. CAP can’t bind to promoter
  4. Binding of RNA pol on promoter is unstable & weak ≠ transcription
20
Q

Explain the effect of Low Glucose levels on the lac operon expression.

A
  1. No glucose = increase cAMP lvls
  2. cAMP - CAP complex forms
  3. complex binds to promoter
  4. Binding of RNA pol is stable = transcription
21
Q

In lac operon control, where does the repressor protein come from?

A

from Lac I gene that is always expressed

22
Q

In mRNA processing, what is meant by the term “alternative splicing”

A
  • different versions of mRNA from the same pre-mRNA due to various ways it is spliced
  • one gene can make many proteins
  • important in development
23
Q

List the genes of E.coli: Lac _ gene

A 
i: repressor
P: promoter
O: operator
Z: B-galactosidase > breakdown lactose
Y: permease > transport lactose in the cell
A: transacetylase
24
Q

What are the 6 points that control gene regulation?

A
  1. DNA structure: heterochromatin/euchromatin
  2. (rate) Transcription
  3. (rate) mRNA processing
  4. RNA stability: half-life
  5. (rate) Translation
  6. (rate) Post-translation modification
25
Q

What is an silencer? Is this cis acting or trans acting?

A

(cis-acting) DNA sequences w/in, up- / down-stream from gene > repress transcription initiation

26
Q

How is gene regulation used in Plasmodium falciparum?

A

(Malaria parasite) hides in RBC by constantly changing the expression of 1 gene (/60 var genes) = 1 antigen => avoid being detected by immune response bc immune can’t keep up w/ changes in antigen

27
Q

How is gene regulation used in same species of fish but live in 2 different locations?

A
  1. Surface lakes = eyes. 2. Cave lakes ≠ eyes (genes for eyes switched off)
  2. Increase expression of genes (sonic hedgehog & tiggy winkle hedgehog) = eyes don’t develop normally
28
Q

What are the types of DNA-binding proteins/motif that can bind to the major groove of DNA?

A
  • helix-turn-helix: 2 alpha helix
  • zinc-finger: a-helix w/ zinc (help protein fold)
  • Leucine zipper: 2 helix w/ leucine residues (acting as zipper)
  • Helix-loop-helix: 2 a-helix separated by loop of AA
29
Q

Describe the 2 component system in activating gene transcription

A
  1. External stimulus => dephosphorylate Sensor protein (transmembrane)
  2. Int. protein kinase removes Pi from ATP
  3. Response regulator protein (intracellular) receives Pi => activate (gene) transcription
30
Q

What is a riboswitch?

A
  • regulatory seq. in mRNA
  • mRNA interact w/ regulatory molecule => 2º structure => covers ribosome binding sites = switched off
  • responsible for ~4% gene regulation in bacteria
31
Q

How promoters, enhancers & silencers affect transcription? (2 stage process)

A
  1. Pre-initiation complex (PIC) assembles by transcription factor (TF) assemble over TATA box of promoter (=> recruits specific TF & RNA pol.)
  2. PIC link w/ TF @ enhancer (upstream) (DNA loops they are in close proximity)
    = aligns RNA pol. => transcription occurs
32
Q

Levels of gene expression in eukaryotes?

A
  1. epigenetic
  2. transcriptional
  3. post-transcriptional
  4. translational
  5. post-translational
33
Q

What are the promoter motifs in eukaryotic cells?

A

Core promoter: TATA box (TATAAAA); Initiator/Inr (YYANRYY)

Regulatory promoter: CAAT box (CAAT); GC box (GGGCGG)

34
Q

Levels of mRNA regulation in eukaryotes

A

transport, processing, translation and degradation of mRNA

35
Q

Difference b/w core promoters & regulatory promoters

A
  • Core: adjacent to transcript. start; controls basic lvl of transcription; specify start & direction of transcription; activated by transcript. factors
  • regulatory: upstream from core promoter; specify enhanced Lvl of transcript.; activated by transcript. activator proteins
36
Q

Lac operon is [inducible OR repressible] and [+ OR - control]

A

inducible (bc can be turned on by lactose)

AND +ve & -ve (bc it can be controlled by an activator & a repressor)

37
Q

Function of DNA-binding domain in DNA-binding protein

A

anchor transcription factor to the proper site on DNA

38
Q

Difference b/w trans acting and cis acting?

A

cis-acting: regulatory regions of operons

trans-acting: factors that bind to regulatory region.

39
Q

What DNA-binding motif does the Lac repressor have?

A

helix-turn-helix

40
Q

General idea of (Trp operon) attenutation

A

rate of translation on leader sequence/peptide (upstream start codon) determines if transcription is terminated.
Trp present = rapid translation = form 3:4 stem-loop = transcription terminated

Mol. Gen. (GENE2000) (14 decks)

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