Lecture 11 Flashcards
1
Q
Prokaryote DNA features
A
- Unicellular
- No membrance bound organelles
- 500-4000bp
- Small genomes
- Circular DNA
2
Q
Eukaryotic DNA features
A
- Uni/multi cellular
- All organelles are membrane bound
- 6000 - 30000bp
- Large genomes
- Linear DNA organised into chromatin
3
Q
Why are eukaryotic genomes so large?
A
- More genes
- Amount of non-coding sequences
4
Q
What are the types of non-coding sequences?
A
- Gene regulatory sequences
- Introns
- Sequences of no known function
5
Q
Interdespersed repitive DNA
A
- Repeated uni scattered through genome
- Simple 100-10,000bp
- 25% of mammalian genome
6
Q
Tandomly repetitive (satellite) DNA
A
- Mainly located at telomeres and centromeres
- Regular - 10,000 - 10 million bp
- Mini - 100 - 100,000 bp
- Micro - 10 - 100 bp
- Causes genetic diseases (huntington’s)
7
Q
Chromatin structure
A
- Composed of chromatin (protein and DNA)
1. Histones (+ charged proteins) bind to (- charged) DNA. 200 bp per histone
2. Condenses further into 30nm of chromatin fibre. This is Euchromatin which is visible and can be transcribed
3. Further condenses into heterochromatin which is too tightly packed for transcription
8
Q
Eukaryotic Gene expression
A
- Genes are continously turned off or on in response to internal/external environments
- Long term control is called cellular differentiation
- Regulation can occur at any step from gene to protein
9
Q
DNA Methylation
A
- Gene silencing
- Methyl group binds to DNA bases
- Triggers more compact chromatin structure
- Genomic imprinting in animals
10
Q
Histone Acetylation
A
- Gene activating
- Acetylated groups to histones
- Acetylated histones grip DNA less tightly
- Turning genes off and on
11
Q
Usually transcription regulation in eukaryotes
A
- Transcription usually begins when RNA polymerase binds to a promotor
- The Tata box provides site of initial promotor binding
12
Q
Preinitation complex
A
- Binding of Tata to Tata binding proteins (TBP) and tata proteins (TAFs)
- Addition of general trasncription factors (TFllA and TFllB)
- Binding of TFllF and RNA polymerase ll
- Followed by binding of TFllE and TFllH to form preinitation complex
13
Q
Transcription regulation
A
- Regulated by “specific transcription factors” which bind to proximal/distol control elements (enhances)
- Enhancers work by folding the DNA to bring distol sequences into proximity with the promotor
- Specific transcription factors have seperate DNA-binding and transcription activation domains
14
Q
Post transcription regulation
A
- Processing of primary transcript
- Capping of 5’ end
- Polyadenylation of 3’ end
- Spicing to remove introns
