lecture 3 : gene organisation + transcription Flashcards
what are the main differences between DNA and RNA?
- RNA uses the sugar ribose instead of deoxyribose - deoxyribose has one less oxygen molecule than the ribose sugar - RNA is generally single stranded instead of double stranded - RNA contains uracil in place of thymine
what are ribonucleotide bases joined by?
- they are joined by phosphodiester bonds
in what direction does the RNA chain grow?
it grows from 5’- 3’ direction
what is an antisense strand?
this is the DNA strand that gets transcribed (it is antisense because it is the opposite of the RNA that is produced)
what carries out transcription?
- RNA polymerases
what else is involved with transcription?
- special gene regulatory factors called transcription factors
what are the three types of RNA polymerase and what do they do?
RNA polymerase i : transcribes rRNA genes
RNA polymerase ii : transcribes mRNA
RNA polymerase iii : transcribes genes encoding protein into tRNA
how is gene regulation achieved?
- DNA synthesis needs an initiation phase first to build the transcription complex - the DNA sequence at where the transcription complex assembles is called the gene promotor (TATA) - the amount of transcription of a gene is regulated by the activity of DNA binding proteins = transcription factors e.g. (TATA binding protein) - transcriptional activators activate the gene activity - transcriptional repressors surprise the gene expression
* what does the basal transcription complex do? and what is the basic anatomy? what is TF iiD?
it produces a low level of transcription in the absence of other transcription factors - also allows RNA polymerase ii to be phosphorylated and then engage in transcription this is TATA binding protein and accessory factors this binds to TATA
* what is the first step of the basal transcription complex?
TF iiD binds to TATA binding site insert image
what happens when TF iiD binds to TATA and the accessory factors?
- partially unwinds the DNA and widens the minor groove … this allows extensive contact with the bases - the unwinding is asymmetrical with respect to TBP- TATA complex - this means the transcription is unidirectional
* what is the second stage of the basal transcription complex? why is this important?
insert pic the TF iiA and TFiiB also bind to the TATA (transcription factor) TF
what is the third stage of basal transcription complex?
insert the pic the RNA polymerase ii binds to the TF iiB and then TFiiF binds to the RNA polymerase ii
what is the fourth stage of basal transcription complex?
insert the pic this is when TF iiE, TF iiH and TF iiJ all bind to RNA polymerase ii
why is TF ii H important?
this promotes further unwinding of the DNA helix to allow the RNA synthesis by RNA polymerase ii
