Gene Regulation Flashcards
What is gene expression and regulation?
- EXPRESSION - turning on gene to produce RNA for protein synthesis
- REGULATION - turning gene on/off for expression
What are transcription factors and how can they activate RNA Polymerase?
- Bind to gene near transcription start site
- Help position RNAP at promoter, aid in pulling apart DNA strands for initiation
Outline the differences between prokaryotic and eukaryotic transcription. PART 1
- PROKARYOTES - 1 RNAP/EUKARYOTES - 3 RNAPs
- EUKARYOTES - RNA contains intron and exon sequences/ PROKARYOTES - no introns so no splicing
Outline the differences between prokaryotic and eukaryotic transcription. PART 2
- PROKARYOTES - gene regulation at transcriptional level
- EUKARYOTES - gene regulation - epigenetic/ after transcription and translation
Describe the sections involved in prokaryotic gene regulation. PART 1
- OPERON - cluster of genes transcribed to give mRNA
- PROMOTER - DNA sequence - RNAP binds to initiate transcription
Describe the sections involved in prokaryotic gene regulation. PART 2
- OPERATOR - downstream of promoter - regulatory molecules bind to regulate gene expression
- Regulatory gene – encode for proteins that regulate gene expression
What does the lac operon code for?
- Enzymes that hydrolyse lactose e.g beta-galactosidase
Describe how lactose concentration affects transcription in the lac operon.
- ABSENCE OF LACTOSE - repressor protein binds to operator and blocks transcription
- PRESENCE OF LACTOSE - repressor protein released from operator/ transcription occurs
Describe how glucose concentrations influence transcription in the lac operon.
- LOW GLUCOSE - cAMP-CAP complex stimulates RNAP activity and increases RNA activity
- Even if glucose present, repressor binds to operator//RNA synthesis blocked
Describe epigenetics in eukaryotes.
- Modifications to DNA to regulate gene expression without changing DNA sequence
- EXAMPLES: methylation/histone modifications
How do DNA methylation and acetylation affect transcriptional activity?
- METHYLATION - nucleosomes are densely packed.
- Promoter regions are less accessible to transcription factors.
- Low transcriptional activity
- OPPOSITE for acetylation
What may cause epigenetic changes?
Drugs
Aging
Diet
What are the 3 eukaryotic RNA polymerases?
- Polymerase I - transcribes rRNA - found in nucleolus
- Polymerase II - synthesises mRNAs, snRNAs, siRNA - in nucleoplasm
- Polymerase III - tRNA, viral RNA - in nucleoplasm
Describe transcription initiation.
- 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.
Why does the TATA box only use adenine and thymine residues?
- 2 hydrogen bonds betwen A and T
- RNAP - less energy to separate strands of double helix
Describe chain elongation.
- 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
Describe chain termination.
- Pol II reaches stop codon/stops elongation
- Pol II/mRNA transcript released from template DNA
- Forms primary transcript pre-mRNA with exonic/intronic sequences
What are the three post-transcriptional modifications? Why are they needed?
- Capping
- Polyadenylation
- RNA splicing
- Stabilise mRNA, protect it from degradation by RNAse during export into cytoplasm
Describe RNA splicing.
- Spliceosomes - small nuclear ribonucleoproteins and recognise splice sites on pre-mRNA
- Introns removed and exons are linked together
Describe alternative splicing.
- Differential splicing by mRNA
- Rearranges patterns of introns and exons
- More than 1 protein product from the same gene
Describe mutation splicing in beta-thalassemia.
- 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
Describe RNA transcript export.
- 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
What is the purpose of enhancers and activators?
- ENHANCERS - increase transcription and can activate promoter sites
- ACTIVATOR - regulatory protein - binds to enhancer and helps RNAP, TFs bind at promoter - increase transcription
What is the purpose of silencers and repressors?
- SILENCERS - DNA sequence - silence expression of gene when bound to TFs
- REPRESSORS - Regulatory Protein that binds to silencer to decrease transcription
