Biochem and medical genetics
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| RNA polymerase | show 🗑
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| show | DNA - deoxyribose sugar, double stranded, contains thymine
RNA - ribose sugar, single stranded, contains uracil
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| show | RNA polymerase synthesises RNA in the 5' to 3' direction
Both strands of DNA can serve as templates, it depends on the direction of the gene
You get different RNA depending on which strand is the template, so it is important the right strand is used
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| Different forms of RNA polymerase | show 🗑
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| Different RNA functions | show 🗑
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| Promotors | show 🗑
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| General Transcription factors | show 🗑
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| show | RNA polymerase is recruited to gene Core promotors
The TBP subunit associates with the TATA box on the gene
TFIIB joins by recognising the BRE sequence
TFIIF recruits pol II and stabilises its interaction with TFIIB and TBP
TFIIE and TFIIH join.
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| show | Has helicase activity to unwind DNA
Has kinase activity that phosphorylates the C-terminal domain of pol II to activate transcription
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| show | In addition to GTFs many other proteins called activations and co-activators are required to ensure correct and regulated expression of genes
These bind to regions outside the core promotor elements
These ensure timely and controlled expression
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| Co-activators | show 🗑
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| Activators | show 🗑
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| show | Locus control region - regulates expression of a cluster of genes to ensure correct sequence of expression
Enhancer - activates expression over long distances
Silencer - represses transcription at promotors
Insulator - regulate expression between genes
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| How do distant sequences affect transcription | show 🗑
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| Heterochromatin | show 🗑
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| show | Loosely wrapped DNA regions containing active genes
DNA can be accessed by GTFs
Chromosomes are loosely packed with methylation of H4, K4 and K36 on histone tails. Acetylation also occurs
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| Modification of Histone tails | show 🗑
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| Constitutive Heterochromatin | show 🗑
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| show | Xist expression on both X chromosomes in female ES cells is unstable. Stabilisation of Xist RNA acetylates, methylates, recruits proteins to histones and coats one X chromosome. The Xist on the active X is then silenced as one chromosome becomes inactive
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| show | regulates gene expression
High CpG methylation frequency
Important for imprinting, transposon silencing and X-inactivation
Cancers have changing methylation patterns
Accessible chromatin unmethylated
Methylated DNA reduces TF affinity
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| How does DNA methylation occur | show 🗑
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| show | Methylated DNA
Heterochromatin
Methylated histones
Tightly compact chromatin by binding of other proteins
Organisation into nuclear lamina associated domains at the edge of the nucleus
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| show | Unmethylated DNA
Euchromatin
Unmethylated and acetylated histones
Chromatin held open by other proteins
Organisation into transcription factories in the centre of the nucleus
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| Example pathway of activating a gene | show 🗑
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| show | Largest subunit of RNA pol II has a structure at its C terminus of 52 repeats of seven amino acids YSPTSPS
Phosphorylation of the serine residues is critical for the transition between initiation and elongation in transcription
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| RNA polymerase II transcription cycle | show 🗑
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