Heather knight Flashcards
What is transcription?
The process by which the complimentary strand (to the strand we want) acts as a template to produce an RNA strand that is complimentary to the template but a copy of the original coding strand.
What is the difference between RNA and DNA?
The form of the sugar riboso vs deoxy
The bases thymine vs uracil
What are some examples of non coding RNAs?
rRNA, tRNA snRNA scRNA miRNA.
RNA and tRNA are involved in translation and various other micro RNA’s have regulatory roles in eukaryotes.
Describe how the structure of RNA is related to its function.
- CLAMP - keeps the polymerase anchored to DNA ( it is made up of jaws)
- FLAP- ensures the mRNA is retained.
DNA does not enter the mouth of the polymerase directly where is it held how does this help force the 2 strands apart?
It is usually held sideways with a sharp bend to its left as it exits the polymerase.
The bending helps force the 2 strands apart.
MRNA is believed to leave from the back of the polymerase.
RNTPs enter the active site at the same side that DNA is pulled through but via a secondary channel.
What is the function of the alpha subunit of bacterial RNA pol?
Helps the polymerase bind to the promoter.
What is the function of the b unit of bacteria RNA polymerase?
Nucleotide binding.
The movement of the chain through the system, base by base, is steered by the rudder formed by the beta subunit.
What is the function of the b’ subunit?
Template binding
What is the function of the s (sigma) unit of bacterial RNA polymerase?
Initiation.
Helps by anchoring the polymerase in the right place to transcribe the gene. It also helps to separate the 2 strands to make the bubble. The sigma factor dissociates once it has performed its functions.
What are the 3 main stages of Transcription?
- Initiation
- Elongation
- Termination
Describe the structure of a bacterial promoter.
The promoters of all bacterial genes have regions of simmilarity,. These ‘consensus sequences’ are similar in all genes studied.
- they are hexameric (6-base) sequences at -35 and -10 bases upstream of the start of transcription these sequences are important in the recognition of the transcription start site but the RNA polymerase.
What does the RNA polymerase HOLOENZYME do when it reaches the -35 and -10 promoter region?
It recognises the consensus sequences and stops and binds to them. This is the job of the sigma factor.
What is step 1 of transcription?
RNA holoenzyme slides along DNA when it recognises the promoter of a gene via the sigma factor it binds tightly.
holoenzyme and DNA undergoes a series of conformational changes that consist of opening up the DNA, positioning it on the enzymes active site and then tightening the girl of the enzyme around it to prevent detachment.
> RNA polymerase starts synthesising the mRNA by opening the double helix.
Why can’t DNA be used to directly make a protein?
DNA is too stable, it requires an unstable intermediate, hence RNA.
