RNA Transcription Flashcards
In which direction is DNA read in and in which direction is RNA synthesised?
DNA is read in the 3’ to 5’ direction and RNA is synthesised in the 5’ to 3’ end.
By convention, is a DNA strand sequence written with the 5’ end on the left or on the right?
On the left.
When only one strand of DNA is referred to, by convention, which strand is being referred to; the template strand or the coding strand?
The coding strand.
What is the difference between polymerases in prokaryotes and eukaryotes?
In prokaryotes, there is only one time of polymerase. In eukaryotes there a three different polymerases. RNA polymerase I, II and III
True or false; a single gene can only be transcribed by only one RNA polymerase molecule at a single time.
False, the same gene normally has many RNA polymerase molecules operating on it at once, one after another.
What are the two types of termination in prokaryotes and what is the difference between them?
Intrinsic and Rho dependent modification.
How is pre-mRNA modified before it becomes mRNA?
- Addition of 7-methylguanosine cap at the 5’ end
- Addition of a 3’ polyA tail
- Splicing to remove introns to bring exons together.
What is the function of the 7-methylguanosine cap at the 5’ end?
- Protects the triphosphate group from hydrolysis by exonucleases
- Allows recognition by ribosomes
What is the purpose pf the 3’ polyA tail?
The 200 A residues added enzymatically to the 3’ end of mRNA:
- increase stability of mRNA (protecting from hydrolysis by exonucleases)
- has a tole in export out of the nucleus
- essential for initiating translation of some mRNAs
What is the difference between monosictronic mRNA and polycistronic mRNA?
Monosictronic mRNA encodes for one protein, while polysictronic mRNA encodes for more than one protein.
What is the difference between mRNA in eukaryotes and in prokaryotes in terms of stability and protein encoding?
mRNA in eukaryotes is stable due to the addition of the 5’ cap and the 3’ polyA tail, while mRNA is prokaryotes is not modified and so is not stable.
mRNA in prokaryotes can be monosictronic or polysictronic, while mRNA in eukaryotes is almost always monosictronic.
How many genes does a typical bacterium have? A human?
Hundreds
20 000
How many genes are there in the human genomes and how many proteins are encoded for?
20 000 genes and 100 000 proteins
What sequences of introns are highly conserved?
GU at 5’ end, AG at 3’ end A at the branching point.
What is the role of the spliceosome?
Bring together the branching point A and the 5’ end of the intron to overcome the natural 3D RNA structure.
