Gene organisation and transcription I Flashcards
What is a gene?
Functional unit of DNA
Encodes information for making proteins and functional RNAs
What does the human genome consist of?
22 pairs of autosomal chromosomes
1 pair of sex chromosomes
Give an example of genes expressed in all cells
Housekeeping genes
Transcription
process of nucleotide information in DNA being copied into RNA
3 steps of transcription
DNA strands unwind
Ribonucleotide base pair with DNA bases on 1 strand
Ribonucleotide bases joined by phosphodiester bonds in 5’ to 3’ direction
Which strand of DNA is transcribed?
Anti-sense
it is anti-sense to the mRNA produced
What are the roles of the 3 types of RNA polymerase?
I – transcribes rRNA genes
II – transcribes genes encoding proteins into mRNA
III – transcribes tRNA and 5S RNA genes
Transcription factors
Special gene regulatory factors
Regulate levels of transcription
Either activator or repressor
Transcription activators
Activate gene expression
Transcriptional repressors
Suppress gene expression
What requires an initiation step and why?
Elongation reaction of RNA synthesis
To build a transcription complex
Gene promotor
DNA complex at which initiation complex assembles
TATA DNA sequence
Specifies initiation point for transcription, after which RNA polymerase II will begin transcription
Basal transcription complex
Allows RNA polymerase II to be phosphorylated and engage in transcription
What constitutes the basal transcription complex?
TFII (D, A, B, F, E, H, J)
and
RNA polymerase II
How does the basal transcription complex form?
TF II D binds to TATA, partially unwinding DNA asymmetrically so transcription is unidirectional
TF II A and TF II B bind
RNA polymerase II and TF II F bind to TF II B
TF II E, TF II H and TF II J bind to RNA polymerase II
What does TF II H promote?
further unwinding of DNA helix
to facilitate RNA synthesis by RNA polymerase II
What do transcription factors bind to?
Transcription factor binding sites
Bend DNA
How do transcription factors facilitate transcription?
Help remodel chromatin by recruiting proteins with enzymatic activity that modify histones
Hyperacetylation of histones
Gene expression
Hypoacetylation of histones
Gene repression
What factors determine TF expression?
Cell lineage
Signals outside cell (hormones, growth factors)
What may arise if TFs are mutated?
Genetic disorders
Cancer
Give 2 examples of cancers which arise from mutated TFs
Leukaemia Breast cancer (over expression of oestrogen receptor)
