DNA transcription Flashcards
What is transcription?
Reading the DNA sequence and making RNA from the information
- enzymatic synthesis of RNA from a DNA template and forms the first step in gene expression
Transcription is the generation of a ______ ____ (____)
messenger RNA (mRNA)
What is translation?
The enzymatic synthesis of protein from a transcribed gene sequence into a functional RNA molecule mRNA
Transcription is _____ by an RNA _____ enzyme complex which requires:
- a ____ template
- _______ (ATP, GTP, CTP & UTP)
catalysed
polymerase
dsDNA
ribonucleotides
RNA synthesis is in the __ to __ direction
5’
3’
What does the sense strand do?
carries the gene sequence that will be copied into an RNA molecule that will be later translated into protein
What does the antisense strand do?
- used as a template to generate a copy of the sense strand through complementary base airing.
- also carries the gene sequence for RNA molecules that are usually non-coding and function as structural/regulatory molecules
In ______ there is a _____ _____ _____
prokaryotes
single RNA polymerase
How many RNA polymerase enzymes are there in eukaryotes?
3 - I, II and III
List what each polymerase is responsible for transcribing different RNAs
I - transcribes most rRNA (ribosomal RNAs)
II - responsible for transcription of all-protein coding genes
III - transcribes tRNAs (transfer RNAs)
What does initiation of transcription involve?
The binding of RNA polymerase complex to the dsDNA
_____ can be switched on ____ or ____ based on the ______ elements present and if they are ______ by bound proteins
Promoters
weakly or strongly
sequence
stimulated
The dsDNA needs to be locally _____ for the RNA polymerase to access the ____ _____
unwound
promoter sequence
What is the site of action known as for when the polymerase starts to synthesise the mRNA at a specific nucleotide?
start site/initiation site
In elongation, the polymerase is moving in the 3’ to 5’ direction along what strand?
antisense/template DNA strand
What happens to the DNA duplex ahead of reformation?
The polymerase locally unwinds the DNA duplex ahead of RNA synthesis activity
The helix is reformed behind the polymerase enzyme
E coli synthesises around ___ bases per ____ at ____ degrees
40
second
37
What stabilises the assemled holoenzyme?
w-subunit
What is responsible for promoter recognition?
σ
What is the most common σ factor in E.coli?
σ70
What is the transcription start site denoted by ?
+1
What is the promotor sequence denoted by?
a negative number since they are before the initiation site
How many base pairs long is the σ70 promoter?
40-60 base pairs
What region has been shown to bind the RNA polymerase holoenzyme?
-55 to +20
What region is very strongly associated with the holoenzyme?
-20 to +20
Sequences up to ____ are required for _____ transcription
-40
efficient
What is the -35 region?
Recognition sequence
What is the -10 region?
DNA unwinding site
List the 5 steps of E.coli transcription
1) Promoter binding
2) DNA unwinding
3) Transcription initiation
4) mRNA elongation
5) Termination
What is common in prokaryotes?
Transcription of a particular gene is controlled by a regulatory region of DNA near the site of transcription
What is common in eukaryotes?
Some regulatory regions are like simple switches, while others are like a microprocessor and respond to a variety of signal inputs
Specific proteins bind to the _____ region of the DNA to turn ___/____ the gene
regulatory
on/off
The proteins bind to the _____ of the DNA by _____ specific sequences
outside
recognising
Bases are mostly on the _____ of the helix but the edges of the base pairs are ______ at the surface
inside
exposed
What do the exposed edges provide opportunities for?
interactions via hydrogen bonding and hydrophobic interactions in both minor & major grooves
Where do most regulatory proteins bind?
In the major groove
Give an example of transcription
lac operon
Explain what lacY, lacZ and lacA allow for
- lacY allows lactose uptake from media
- lacZ converts lactose to glucose & galactose (main reaction) and Allolactose (side reaction)
- lacA physiological function in lactose metabolism unknown
