DNA Transcription Flashcards
(37 cards)
Describe the idea of the central dogma.
Describes transcription and translation, in which information goes from DNA to RNA to protein.
Therefore there is only 1 flow of direction.
An exception - some viruses which has a specific enzyme that is able to revert the direction and transfer RNA to DNA molecules - Retrovirus, e.g. HIV.
What structure is RNA usually found in?
RNA closes up by forming double strand regions between more than 1 RNA molecule or within 1 molecule.
RNA is in theory a linear nucleic acid but will never be found as a line of nucleotides in reality. They will always be found as very complex structures.
What is the function of RNA Polymerase?
To carry out transcription.
Describe main features of RNA Polymerase.
Large proteins with different active sites.
Needs magnesium ions on active sites to work.
Need to unwind DNA in order to read template strands and copy to newly synthesized transcripts.
Work only 5’ to 3’ directions.
How many proteins can 1 gene produce at the same time?
From one gene, thousands of RNA molecules transcribed at the same time.
What are the 3 stages of transcription?
Initiation
Elongation
Termination
Describe the process of prokaryotic transcription.
The sigma factor (initiation factor) binds to DNA, then to RNA polymerase to form a closed complex at the promoter.
The complex opens and DNA is unwound. Abortive initiation proceeds where RNA polymerase transcribes small pieces of RNA, which is discarded.
Sigma factor is released, marking the end of initiation.
RNA is continiously transcribed (elongation) until hairpin structure are formed in RNA from binding of other factors, this stops RNA polymerase.
RNA and DNA are released, DNA will be recycled.
Describe how general transcription factors initiate transcription at the TATA box.
A complex of TFIID and TBP binds to the TATA box. TFIIB also binds to the complex.
TFIIE and TFIIH arrives, a RNA polymerase bound to TFIIF also arrives.
Some factos are released, while precursors of RNA synthesis arrives in the form of triphosphate ribonucleotide.
The CTD of RNA polymerase II is phosphorylated to start transcripion by TFIIH.
What are enhancers?
A short region of DNA that can be bound by proteins to increase the likelihood that transcription of a particular gene will occur.
What is the function of elongation factors?
Reduce the probability that RNA Polymerase dissociates prematurely from DNA.
What are activators?
A protein that increases gene transcription.
What are repressors?
A protein that inhibits gene transcription.
Where is the initiation complex assembled?
At the promoter.
What are silencers?
A DNA sequence capable of binding transcription regulation factors, called repressors, that works to inhibit transcription.
How does the binding of TBP to DNA help other factors bind?
Its binding causes bending in DNA structure that indicates binding sites for other transcription factors.
Describe prokaryotic mRNA.
One mRNA translated to 3 separate proteins. They are usually related in function. This is defined as polycistronic - contains more than 1 protein sequence.
This is due to size - viral genes small so all sequences employed to be transcribed. Very small regions are non-coding.
Describe eukaryotic mRNA.
Lots of space so no problem of using the whole genome.
Usually single mRNAs encoding 1 protein.
5’ + 3’ modifications present in mRNAs - polyadenylation - addition of a long chain of adenine to 3’ end.
5’ capping - addition of 8-methyl; guanosine residue at 5’ direction.
Particular bridge (triphosphate bridge) as methylated.
How does superhelical tension relate to transcription?
Transcription creates superhelical tension, therefore specific proteins are needed to buffer this tension.
What are the functions of 3 RNA polymerases in eukaryotes?
Polymerase I: Involved in producing ribosomal RNA.
Polymerase II: Transcribes all mRNA, snoRNA genes and other non-coding RNAs.
Polymerase III: Synthesis of tRNAs and some ribosomal RNAs, also other calsses of small non-coding RNAs.
Describe prokaryotic transcription and translation.
DNA translated into RNA and then protein.
Happens in the cytoplasm, everything happens at almost the same time as no separation between DNA and other components.
Nothing happens to mRNA up to transcription, no modifications applied to it.
Describe eukaryotic transcription and translation.
Have nucleus where DNA transcribed, therefore RNA will need to pass nuclear membrane to go to cytoplasm to ribosomes.
Many things happen to RNA before ready for translation - undergoes several processes before sending outside.
DNA transcribed much longer than final messenger RNA to export.
DNA copy will be transcribed into RNA the exact copy of DNA, which is much longer than final mRNA.
RNA Splicing has to occur and cut RNA transcript to make it shorter.
Chemical modification at beginning 5’ and end 3’. mRNA will need to be escorted.
Describe eukaryotic transcription and translation.
Have nucleus where DNA transcribed, therefore RNA will need to pass nuclear membrane to go to cytoplasm to ribosomes.
Many things happen to RNA before ready for translation - undergoes several processes before sending outside.
DNA transcribed much longer than final messenger RNA to export. RNA Splicing has to occur and cut RNA transcript to make it shorter.
When does RNA processing happen?
During elongation, they are processed as soon as possible after transcription initiation.
How are proteins able to reach RNAs during transcription?
CTD residues of RNA polymerase are phosphorylated to allow different proteins to bind, so that they can bind to RNA as soon as they can reach.
