Intro to gene expression control Flashcards
Understand: - levels of gene expression control (ex: thalassaemia) - translational control - regulation of RNA stability by microRNAs
How is differential gene expression regulated in time? [2 marks]
- Embryonic gene expression differs from gene expression in adults
- It differs in response to hormones, infections and other signals
How is differental gene expression regulated in space? [1 mark]
Different tissues/cell types express different genes
What happens if genes for metabolism are not tightly regulated? [1 mark]
Metabolic diseases (e.g. diabetes mellitus) can arise
What happens if genes for cell shape/mobility are not tightly regulated? [2 marks]
- Cells may move faster or to other tissues
- This can cause cancer metastasis
What happens if genes for cell regulation are not tightly regulated? [1 mark]
Congential diseases can arise
What happens if genes for cell proliferation are not tightly regulated? [3 marks]
- Cells can go through the cycle faster
- Cells can skip checkpoints
- Causing cancer
What is the bithorax complex? [3 marks]
- Group of homoeotic genes in Drosophila melanogaster
- Controls the differentiation of the thorax
- Mutations cause drosophila to have 2 thoraxes, wings and stomachs
What is antennapedia?
- Gene that controls the formation of legs
- Mutation causes legs instead of antenna to form at the front
What are totipotent cells? [2 marks]
- Can produce all cell types
- Both somatic cells and extra-embryonic parts (e.g. placenta, membrane)
What are pluripotent cells? [1 mark]
- Can produce several functional cell types (e.g. bone marrow stem cells)
How to reprogram cells back to pluripotent cells? [1 mark]
Add transcription factors
Post transcriptional regulatory steps [5 marks]
- Capping
- Polyadenylation
- Splicing
- Nuclear transport
- Translation
What happens if there is a mutation in the promoter region? [1 mark]
The gene can’t be expressed
What happens if there is a mutation in the intron? [2 marks]
- It cannot be spliced by the spliceosome
- A specific sequence in the intron must be recognised by the spliceosome
When does gene expression in embryos occur and how? [2 marks]
- At the end of blastocyst formation
- Due to up-regulation of translation from maternal pre formed mRNA
Environmental stresses that control translation? [2 marks]
- Heat shock
- Pathogens
First codon in frame [1 mark]
AUG
What is the Kozak sequence? [2 marks]
- Sequence in 5’ UTR
- Guides ribosome to the first AUG after it
What does the preinitiation complex contain? [4 marks]
- Small ribosomal subunit (40S)
- eIF1
- eIF2-Met-tRNAi-GTP complex
- eIF3
What is the function of eIF3 [2 marks]
- Associates with 40S subunit
- Binds near E site
What is the function of eIF2? [3 marks]
- Associates with Met-tRNAi and GTP
- Combines to form 48S subunit
- Binds near P site
What is the function of eIF1? [2 marks]
- Binds to 40S subunit to stabilise “open” confirmation of the preinitiation complex
- Binds near A site
What regulates the efficiency of translation? [3 marks]
- eIF3
- eIF4
- Cap
Function of ferritin and its gene expression [3 marks]
- Binds to excess iron
- Retains it in the cytoplasm as a store
- Translated very poorly
Ferritin mRNA in low iron [3 marks]
- 5’ UTR forms a loop
- Ribosome can’t go past loop
- Loop recognised by iron starvation inhibitor
Ferritin mRNA in high iron [4 marks]
- Iron binds to inhibitor
- Inhibitor leaves mRNA
- Ribosome undoes loop
- Translation is fast
What are micro RNAs (miRNAs)? [4 marks]
- Small non coding RNAs
- Regulate post transcriptional regulation of almost 1/3 of human genes
- Usually by blocking translation of selective mRNAs
- One miRNA can regulate several target genes
What are miRNAs made from and how? [2 marks]
- Cytolytic enzymes cleave off ends and signal peptide of precursor miRNA
- Short dsRNA molecule recognised by RNA Induced Silencing Complexes (RISC)
What does RISC do afterwards? [2 marks}
- RISC binds and unwinds RNA molecule
- RISC forms complex with antiparallel strand
Extensive match v. less extensive match
Extensive = mRNA is rapidly degraded and RISC is released
Less extensive = Ribosome is stopped, mRNA is sequestered and then degraded
