Transcription (1 & 2) Flashcards
What is transcription?
The copy of information from a DNA sequence (a gene) to a complementary RNA sequence
What is translation?
The conversion of an RNA sequence to an amino acid sequence of polypeptides
How does RNA differ from DNA?
RNA has one polynucleotide chain with secondary structures (hairpins, loops); the sugar is ribose; bases can pair with a single strand of DNA; can fold into complex shapes by internal base pairing; contains uracil instead of thymine
Why does RNA contain uracil and not thymine?
Uracil is energetically less expensive to produce than thymine
What direction is RNA synthesised in?
5’ - 3’ direction
What are the different types of RNA?
snRNA (spicing of mRNA); tRNA (adaptor between amino acids and mRNA sequences); mRNA (contains protein coding sequence from gene); miRNA (inhibits translation); rRNA (structural and catalytic component of ribosome)
What are the components needed for transcription?
a DNA template for base pairings; nucleoside triphosphates (ATP, GTP, CTP, UTP) as substrates; a RNA polymerase enzyme; basic features of a gene
What does RNA polymerase catalyse?
Synthesis of RNA
Does RNA polymerase need a primer?
No
RNA polymerase is recruited by the promoter needed for initiation by what?
Transcription factors that bind to the promoter
What happens (in inititation) after the promoter has located RNA polymerase?
RNA polymerase will bind to the promoter and unwind DNA
In elongation, what direction does RNA polymerase read the template strand?
3’ - 5’ direction
What end does the RNA transcript add nucleotides to the template strand?
The 3’ end
Describe what happens in termination?
When RNA polymerase reaches the termination site, the RNA transcript is set free from the template.
What are the four subunits of E.coli core RNA polymerase?
2 alpha units and one beta unit and one beta’ unit
What is holoenzyme and what does it do?
It is formed by the combination of an enzyme with a coenzyme and cn recognise and bind the promoter
What role do sigma factors play in intiation?
They bind consensus sequences in the core promoter
What happens to signma factors in elongation?
They are released
Are transcripts longer or shorter in elongation?
Longer (because sigma factor are released as they only allow short abortive transcripts to be synthesised)
What cause the RNA polymerase to stall in termination?
The form of a hairpin loop from the palindromic sequence
What is TFIIB?
It is a general transcription factor that is involved in the formation of the RNA polymerase II preinitiation complex and aids in stimulating transcription initiation
What is TFIIE?
It is one of several general transcription factors that make up the RNA polymerase II pre-initiation complex.
What is TFIIH?
It is an important protein complex, having roles in transcription of various protein-coding genes and DNA nucleotide excision repair pathway
Can TFIIB initiate transcription?
No, even though it has recruited RNA polymerase II?
