Transcription and Translation Flashcards
What is a central dogma?
The central dogma of molecular biology describes the flow of genetic information in cells from DNA to messenger RNA (mRNA) to protein
Describe the difference between the C4 (4th carbon) in ribonucleic acids and deoxyribonucleic acids.
RNA has ribonucleic acid which has an OH group on the 4th carbon whereas deoxyribose has no OH and is only a H attached to the C4
Describe the process of DNA transcription.
-INitiation
-Elongation
-Termination
-RNA polymerase attaches to a recognition site
-Binding causes the double helix to unwind, forming a transcription bubble
-Complementary bases pair up
Nucleotides linked to the three prime end of the growing RNA molecule
-RNA polymerase dissociates one the terminator sequence has been reached
What causes torsional strain on the DNA during transcription?
DNA leaves the RNA polymerase at an angle which causes a torsional strain
What is the function of the ‘flap’ in RNA polymerase?
Flap is a door at the back of the enzyme to stop the RNA falling out of place whilst it is still being synthesised
What is the rudder in RNA polymerase?
Mechanism to steer the DNA through, base by base
What are the 5 subunits of bacterial RNA polymerase? What does each do?
- Sigma- initiation of transcription
- Omega-function under dispute
- Alpha- promotes binding
- Beta- binds nucleotides and allows ribonuceotides come in through the ‘tunnel’ by which they must enter
- Beta’- template binding, holding on to the DNA
What is meant by the ‘core enzyme’ with respect to RNA polymerase?
When the sigma subunit leaves the holoenzyme
Describe what occurs in the initiation stage of transcription.
- Cosensor sequences at the -10 and -35 positions are recognised
- Recognised and bound by a subunit of RNA polymerase
- Base pairs separate here
What is meant by a co-sensor sequence?
‘Boxes’ such as the -10 and -35 boxes which are regions upstream of transcription which are recognised by NRA polymerase during initiation (which have positions of about 10 and 35 base pairs away from the promoter region)
What is meant by a consensus sequence?
‘Boxes’ such as the -10 and -35 boxes which are regions upstream of transcription which are recognised by NRA polymerase during initiation (which have positions of about 10 and 35 base pairs away from the promoter region)
What direction does transcription occur in?
5’ to 3’ direction
When is the sigma factor of RNA polymerase ejected?
Sigma factor gets ejected once the formation of RNA is underway (not needed after the first stage)
How can RNA polymerase get away with having a proof reading activity that is not as effective as DNA polymerase?
It is not as important if there are a few mistakes made by RNA polymerase because if there is a faulty transcript the error will not be perpetuated many times and also it will more likely lead to a non functional enzyme or a piece of RNA that cannot be translated
Describe the two different processes of termination in transcription.
Rho independent (intrinsic termination)
- Many A’s on DNA complementary base pair to many U’s on RNA
- Hairpin loop forms
- Makes RNA polymerase dissociate by affecting the active site so it can no longer hold onto the RNA
Rho dependent termination
- Rho is a helicase which moves behind RNA polymerase
- When a hairpin loop forms and the polymerase reaches it, it stalls and the rho protein catches up
- Rho breaks the bonds between the UUUU and AAAA (etc) sequence
- RNA released form active site
Give examples of catabolic and biosynthetic operons.
Catabolic- lac operon
Biosynthetic- tryptophan operon
What happens to the lac operon in the presence of lactose (if no glucose is present)?
It gets switched on.
What is a sigma factor?
It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase to gene promoters. … Once initiation of RNA transcription is complete, the sigma factor can leave the complex.
What are the two monosaccharides that from lactose?
Galactose and glucose
Which enzyme cleaves lactose?
Beta galactosidase, breaks the glycosidic bond.
Which enzyme neutralises toxic sugars accidentally made by beta galactosidase?
Transacetylase
What is lacI?
The repressor which is bound to the promoter for the lacZYA operon