Lecture 10 Flashcards
Outline the general process of Transcription
- RNA polymerase, together with one or more transcription factors, binds to promoter DNA
- RNA polymerase creates a transcription bubble, which separates the two strands of DNA helix by breaking the hydrogen bonds between complementary DNA nucleotides
- RNA polymerase adds RNA nucleotides complementary to DNA
strand - RNA sugar-phosphate backbone forms with assistance from RNA polymerase to form a new RNA strand
- Hydrogen bonds of the RNA-DNA helix break, freeing the new RNA strand
- In eukaryotes post transcriptional processing includes polyadenylation, 5’ capping, and splicing
- The RNA may remain in the nucleus or exit to the cytoplasm through the nuclear pore matrix via
What is responsible for all of the catalytic action of transcription? what else is involved in transcription?
RNA Polymerase II ; activator proteins
Does Transcription create superhelical tension?
yes, topoisomerase relieves the tension
When are new mRNA capped?
They are capped as soon as they emerge from the RNA polymerase
What must occur once the RNA polymerase is finished with one mRNA strand, before it can begin another round of transcription?
It must be dephosphorylated
“what are the steps involved in eukaryote mRNA processing prior to leaving the nucleus?”
5’ capping
RNA splicing (removes intron sequences ; lariats are formed here)
3’ polyadenylation (poly A tail)
What are the steps in capping mRNA? When does mRNA capping begin?
The 1st nucleotide is dephosphorylated
GMP is added in reverse linkage (5’ to 5’ instead of 5’ to 3’)
A methyl group is added to the guanosine
Capping begins when the mRNA is 25 nucleotides long
Explain how Introns are ID’ed and removed during splicing
Introns are flanked by sequences that are recognized by spliceosome RNA’s to ID where the cut needs to happen, and then RNA brings in other proteins to actually cut the intron out.
what performs splicing?
spliceosomes
explain the process of splicing
the 5’ end of the intron is ID’ed
the “A” near the 3’ splice site of the intron in ID’ed
the Lariat structure is formed
the 3’ end of the intron is cut
the 2 exons are then joined
Spliceosomes do not need to use ATP because they use energy already stored in the intron to exon bonds. True or False
False ; spliceosomes use ATP
List the 5 types of snRNP’s and what they are involved in
U1: ID’s 5’ end of intron
U2: binds to A
U4 and U5: work together to recruit proteins to make the conformational and enzymatic changes in splicing
U6: recognizes the 3’ end and works with U4 and U5
(there is no U3)
Why are mRNA sequences given a poly A tail?
it increases the stability of the sequence and makes it easier to be transported without being damaged.
define Consensus sequences in the process of transcription
signal that the mRNA needs to be clipped (this sequence is complete)
What is an exosome in the nucleus?
a protein complex that uses RNAses to digest damaged RNA sequences so that their nucleotides can be recycled