Gene Expression Flashcards
What is the central dogma of molecular biology?
DNA transcribed into RNA
RNA translated int protein
Exceptions: reteroviruses (reverse transcriptase turns RNA into DNA, non-coding RNA such as tRNA, rRNA and miRNA)
Define a gene and describe its structure:
Definition: unit of inheritance, mainly but not always coding for a protein, sequence of DNA gives an inheritable trait
Structure:
- exons and introns
- RNA coding region (contains protein coding region and untranslated region at start and end)
- Cap addition side (adds protective nucleotide)
- PolyA addition (adds nucletide to protect RNA)
Descibre the 3 steps of translation:
- Initiation: RNA polymerase II to start of gene, pulls DNA strands apart
- Elongation: RNA polymerase travels along DNA making RNA (forms a transcription bubble)
- Termination: RNA synthesis stops, detaches form DNA, DNA returns to double stranded
How is pre- mRNA processed?
Immediately in nucleus:
Pre-mRNA contains introns which are removed by splicing.
5’ cap and 3’ polyA tail added
Forms mRNA which is exported to cytoplasm
Define a transcription factor and give examples:
Define: a protein which binds to small specific DNA sequences and influence gene expression
Examples:
- p53 and E2F control cell cycle
- Nuclear hormone receptors-ligand-dependent transcription factors
- Steroids act as TFs
How is gene expression regulated (activation and repression)?
Initiation: Transcription initiation complex
- RNA polymerase can’t bind directly to DNA
- General or basal TF act as bridge between DNA and RNA polymerase
- TF upstream of enhancer elements further stabilise complex
- CAT and TATA box on promoter region
Regulation of transcription: enhancers and repressors
- DNA sequence where TF bind affecting rate of transcription, near or close to gene, make it more or less likely that promoter is activated, required for expression of most genes, basal TF always needed, repressor present means no transcripition
Higher level regulation:
- Closed vs open DNA: not always accessible to TF as coiled around histones to form nucleosomes
- Super-enhancers: locus control regions spanning several genes
Give examples of activators and repressors:
- p53 = activator of transcription of p21 leading to cell cycle arrest and DNA repair, repressor of transcription of survivin leads to apoptosis
- E2F activator of transcription of genes needed for S phase
- Oct-1: repressor of TSH
- Snail: repressor of E-cadherin in epithelial cancers -> increased invasive ability
What are inducible and constitutive genes?
Inducible genes:
- Only expressed in certain tissues/ cells at certain times
- Spatiotemporal gene expression
- E.g. lots of protein coding genes, cell specific (CD4, CD8, collagen I and II, globin, myelin), time specific (cyclins, melatonin, foetal-globin, inflammatory cytokines)
Constitutive genes:
- Genes expressed in all cells at all times at about the same level
- AKA housekeeping genes as maintain basic cell function
E.g. beta-actin (microfilaments), ribosomal protiens
How does one gene code for multiple different proteins?
Alternative splicing:
- Protein coding genes can produce multiple isoforms (different mRNAs from same gene)
- can remove some (or part of an) exons, insert exons, leave in some introns
- Many mutations affect splicing and cause disease
Define genome, transcriptome and proteome
Genome: collection of genes in any one cell
Transcriptome: collection of mRNA in any one cell (more transcriptome than genes due to alternative splicing)
Proteome: collection of proteins in any one cell
Clinical relevance of genome, transcriptome and proteome
Genome: show if patient is expressing normal or mutant protein, sequence of regulatory elements shows how much of a protein can be expressed, does patient have mutations associated with disease
Transcriptome: useful at identifying pathways acting in cell/ tissues, differentiate between different disease, breast cancer
Proteome: can be profiled and used for diagnosis, prognosis and treatment
