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Molecular Genetics > Week 11 - Gene Regulation > Flashcards

Week 11 - Gene Regulation Flashcards

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1
Q

Examples of Control Points

A 
DNA Structure
Transcription 
mRNA processing
RNA stability 
Translation 
Post-translation modification
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2
Q

DNA Binding Proteins

A

Proteins with discrete domains that bind to DNA
- binding domains 60-90 nt
- form H-bonds with bases or interact with sugar-phosphate backbone
Dynamic interaction

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3
Q

Riboswitches

A

Regulatory sequence in mRNA
Influence formation of secondary structures
Usually in 5’ UTR of mRNA
Form compact stem and hairpin loop structures
Stabilised by binding of a small regulatory molecule
- creates terminator signal
- masks a ribsome binding site

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4
Q

Two-component Systems

A

Involve 2 proteins
- one transmembrane sensor protein
- one intracellular response regulator protein
Sensor protein
- becomes externally dephosphorylated in response to a stimulus
- internal protein kinase acquires phosphate from ATP
Response Regulator Protein
- receives P from protein kinase
- activates gene transcription

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5
Q

Hormones

A

Animal equivalent of responding to environmental condition
Steroid hormones diffuse across cell membrane
Interact with hormone receptor
Complex binds to DNA to regulate gene expression

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6
Q

Gene Regulation Categories

A

Inducible - genes that are normally off but can be switched on
Constitutive - genes that are always on
Repressible - genes that are normally on but can be switched off
Both inducible and repressible can be under positive and negative control
Positive - gene expression controlled by activator
Negative - gene expression controlled by a repressor

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7
Q

Cis and Trans

A

Cis - next to or on same DNA strand as gene it controls

Trans - across from and refers to a mobile factor that can act from anywhere

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8
Q

Gene Regulation in Prokaryotes: Operons

A

Control is at transcription
Operon theory of gene regulation:
- genes expressed in groups at a single regulatory region
- regulatory region upstream from gene
- transcription factors bind to regulatory region and control transcription
Regulatory regions of operons are cis-acting elements
Factors that bind to the regulatory region are trans-acting elements

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9
Q

Lac Operon of E.coli

A

Controls metabolism of lactose

3 structural genes - repressor, promoter and operator regulatory region

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10
Q

Lac Operon - No lactose present

A

No enzymes produced

  • repressor protein expressed
  • binds to operator
  • RNA pol binds to promoter but can’t transcribe past repressor
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11
Q

Lac Operon - Lactose present

A

Enzymes produced
Lactose metabolised
- repressor protein expressed
- lactose acts as inducer and binds to repressor causing allosteric shift
- repressor can’t bind to operator
- RNA pol binds to promoter and transcription proceeds
- lactose converted to galactose and glucose

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12
Q

Lac Operon - Glucose and lactose present

A 
No enzymes produced
Lactose not metabolised
- no cAMP present
- no cAMP-CAP complex formed
- CAP can't bind to promoter
- RNA polymerase binding is weak
- transcription doesn't occur
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13
Q

Function of the cAMP-CAP complex

A

Binds to promoter and stabilises binding of RNA pol to promoter

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14
Q

Tryptophan Operon

A

Repressible
Two levels of control
- Allosterically activated repressor
- Attenuation

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15
Q

Trp Operon Allosterically activated Repressor - Tryptophan absent

A
  • repressor protein produced
  • can’t bind to operator
  • RNA pol binds to promoter and transcription proceeds
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16
Q

Trp Operon Allosterically activated Repressor - Tryptophan present

A
  • repressor protein produced
  • inducer binds to repressor, causing allosteric shift
  • altered repressor binds to operator
  • transcription can’t proceed
17
Q

Trp Operon Attenuation

A

mRNA transcript of leader sequence can form either of two stem-loop structures
One allows transcription to continue and other doesn’t

18
Q

Trp Operon Attenuation - Tryptophan present

A 
Trp-charged tRNA available 
Ribosome moves quickly to next codons
Prevents formation of 2:3 stem-loop
Transcription stops
PHOTO page 43
19
Q

Trp Operon Attenuation - Tryptophan absent

A

Trp-charged tRNA scarce and takes long time to arrive
Ribosome stalled allowing 2:3 loop to form
Transcription continues
PHOTO page 44

20
Q

Sequence Dependent Promoters

A

Recognition site for machinery of transcription
Two types:
- core
- regulatory

21
Q

Common Characteristics of Promoters

A

Essential for efficient transcription
Mutations in this region alter transcription rate
Number and location varies

22
Q

Core Promoters

A 
Specify:
- basal level of transcription
- start site of transcription
- direction of transcription 
Activated by general transcription factors
23
Q

Regulatory Promoters

A

Specify enhanced level of transcription
Work in either orientation
Activated by transcriptional activator proteins

24
Q

Enhancers

A

Essential to achieve maximum possible level of transcription
Control time and tissue specific transcription
Interact with multiple regulatory proteins and transcriptional activator proteins

25
Q

Key features of Enhancers

A

Position related to a gene is not fixed
Orientation can be inverted
Can be moved to another gene and still work
Different enhancers have different enhancement capability

26
Q

Silencers

A

Repress transcription initiation

27
Q

Transcription Factors

A

Act on promoters
Trans-acting
Can be expressed in tissue specific or time dependent manner

28
Q

How do promoters, enhancers and silencers affect transcription?

A

Two stage process

  1. Assembly of pre-initiation complex
    - general TF’s assemble at TATA box of promoter and forms PIC
    - recruits RNA pol 2
  2. Interaction between PIC, RNA pol and TF’s
    - activator proteins create link between enhancer TF’s and PIC basal TF’s by looping DNA to bring both complexes close to each other
29
Q

Chromatin Remodelling

A

Altering association of DNA with histone proteins in nucleosomes to allow transcription
Steps:
- loosening of DNA wound around histone core
- temporary separation of DNA from histone core
- dividing histone core into two, exposing central DNA

30
Q

Alternative Splicing

A 
Formation of different versions of mRNA from the same pre-mRNA molcules
Changes in splicing can alter:
- enzyme activity 
- receptor binding capacity
- protein localisation in cell

Molecular Genetics (5 decks)

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