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Karan - MBBS Year 1: Principles Week 2 > Gene Regulation > Flashcards

Gene Regulation Flashcards

1
Q

What is gene expression and regulation?

A
  • EXPRESSION - turning on gene to produce RNA for protein synthesis
  • REGULATION - turning gene on/off for expression
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2
Q

What are transcription factors and how can they activate RNA Polymerase?

A
  • Bind to gene near transcription start site
  • Help position RNAP at promoter, aid in pulling apart DNA strands for initiation
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3
Q

Outline the differences between prokaryotic and eukaryotic transcription. PART 1

A
  • PROKARYOTES - 1 RNAP/EUKARYOTES - 3 RNAPs
  • EUKARYOTES - RNA contains intron and exon sequences/ PROKARYOTES - no introns so no splicing
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4
Q

Outline the differences between prokaryotic and eukaryotic transcription. PART 2

A
  • PROKARYOTES - gene regulation at transcriptional level
  • EUKARYOTES - gene regulation - epigenetic/ after transcription and translation
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5
Q

Describe the sections involved in prokaryotic gene regulation. PART 1

A
  • OPERON - cluster of genes transcribed to give mRNA
  • PROMOTER - DNA sequence - RNAP binds to initiate transcription
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6
Q

Describe the sections involved in prokaryotic gene regulation. PART 2

A
  • OPERATOR - downstream of promoter - regulatory molecules bind to regulate gene expression
  • Regulatory gene – encode for proteins that regulate gene expression
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7
Q

What does the lac operon code for?

A
  • Enzymes that hydrolyse lactose e.g beta-galactosidase
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8
Q

Describe how lactose concentration affects transcription in the lac operon.

A
  • ABSENCE OF LACTOSE - repressor protein binds to operator and blocks transcription
  • PRESENCE OF LACTOSE - repressor protein released from operator/ transcription occurs
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9
Q

Describe how glucose concentrations influence transcription in the lac operon.

A
  • LOW GLUCOSE - cAMP-CAP complex stimulates RNAP activity and increases RNA activity
  • Even if glucose present, repressor binds to operator//RNA synthesis blocked
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10
Q

Describe epigenetics in eukaryotes.

A
  • Modifications to DNA to regulate gene expression without changing DNA sequence
  • EXAMPLES: methylation/histone modifications
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11
Q

How do DNA methylation and acetylation affect transcriptional activity?

A
  • METHYLATION - nucleosomes are densely packed.
  • Promoter regions are less accessible to transcription factors.
  • Low transcriptional activity
  • OPPOSITE for acetylation
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12
Q

What may cause epigenetic changes?

A

Drugs
Aging
Diet

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13
Q

What are the 3 eukaryotic RNA polymerases?

A
  • Polymerase I - transcribes rRNA - found in nucleolus
  • Polymerase II - synthesises mRNAs, snRNAs, siRNA - in nucleoplasm
  • Polymerase III - tRNA, viral RNA - in nucleoplasm
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14
Q

Describe transcription initiation.

A
  • TFIID binds to TATA box upstream from transcription start site
  • Recruits other TF and RNA Pol II to assemble PIC
  • TFIIH recruited to aid DNA strand separation - form open complex
  • mRNA synthesised from nTPs. Once specific length reached, elongation begins.
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15
Q

Why does the TATA box only use adenine and thymine residues?

A
  • 2 hydrogen bonds betwen A and T
  • RNAP - less energy to separate strands of double helix
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16
Q

Describe chain elongation.

A
  • Pol II binds new elongation factors/unwinds dsDNA to expose template for RNA synthesis
  • Proofreading - select correct NTPs to enter active site
  • RNA-DNA hybrid base pairs formed
  • Nascent RNA transcript 5’ capped
17
Q

Describe chain termination.

A
  • Pol II reaches stop codon/stops elongation
  • Pol II/mRNA transcript released from template DNA
  • Forms primary transcript pre-mRNA with exonic/intronic sequences
18
Q

What are the three post-transcriptional modifications? Why are they needed?

A
  • Capping
  • Polyadenylation
  • RNA splicing
  • Stabilise mRNA, protect it from degradation by RNAse during export into cytoplasm
19
Q

Describe RNA splicing.

A
  • Spliceosomes - small nuclear ribonucleoproteins and recognise splice sites on pre-mRNA
  • Introns removed and exons are linked together
20
Q

Describe alternative splicing.

A
  • Differential splicing by mRNA
  • Rearranges patterns of introns and exons
  • More than 1 protein product from the same gene
21
Q

Describe mutation splicing in beta-thalassemia.

A
  • Different types of mutations in beta-globin primary RNA transcript cause condition
  • Exon 2 is skipped, cryptic sites used as partner site, incorporate new exon site
22
Q

Describe RNA transcript export.

A
  • Proteins associated with mRNA mark it for export
  • Only mature mRNA can be exported - exit via nuclear pore complexes to cytoplasm for translation
  • miRNAs binds to 5’/3’ ends to influence stability
23
Q

What is the purpose of enhancers and activators?

A
  • ENHANCERS - increase transcription and can activate promoter sites
  • ACTIVATOR - regulatory protein - binds to enhancer and helps RNAP, TFs bind at promoter - increase transcription
24
Q

What is the purpose of silencers and repressors?

A
  • SILENCERS - DNA sequence - silence expression of gene when bound to TFs
  • REPRESSORS - Regulatory Protein that binds to silencer to decrease transcription
25
Q

What are coactivators and corepressors?

A
  • COACTIVATORS - interact with RNAP, TFs in PIC to activate transcription
  • COREPRESSORS interact to do the opposite
26
Q

What is positive vs negative gene regulation?

A
  • POSITIVE REGULATION - Binding of activator protein promotes transcription
  • NEGATIVE REGULATION - Binding of repressor protein inhibits transcription
27
Q

How do steroid hormones e.g corticosteroids, glucocorticoids regulate gene expression? PART 1

A
  • Steroid hormones translocate into target cell
  • Hormone binds receptor-chaperonin complex, forming receptor-hormone complex
  • Molecular chaperons released, allow binding to DNA
28
Q

How do steroid hormones e.g corticosteroids, glucocorticoids regulate gene expression? PART 2

A
  • Receptor-hormone complex binds to DNA-associated receptor on promotor/enhancer and activates gene expression
  • mRNA is translated

Karan - MBBS Year 1: Principles Week 2 (12 decks)

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