Card Set Information
dna rna transcription
prokaryotic and eukaryotic transcription
3 phases of transcription
initiation, elongation, termination
template for transcription
a single strand of DNA
Substrates for transcription
ATP, GTP, CTP, UTP
Which direction does RNA synthesis proceed?
5'->3', just like everything else...
What's the difference between DNA and RNA polymerases?
RNA polymerases have no other associated activities, like proofreading.
What part(s) of the RNA polymerase is required for elongation in prokaryotes?
only the core enzyme
What part(s) of the RNA polymerase is required for initiation?
the holoenzyme, which is the core enzyme plus the additional
purpose of nuclear RNAs
to synthesize different RNAs
How many and what type of RNA polymerases do eukaryotes have?
one mitochondrial and three nuclear RNA pols. The three nuclear RNA pols have different sensitivities to amanitin
True/false: Both DNA and RNA synthesis requires a primer
False. RNA synthesis (aka transciption) does not require a primer.
Which nuclear RNA is very sensitive to amanitin and what does it make?
hnRNA (=mRNA) and some snRNAs
Which nuclear RNA is moderately sensitive to amanitin and what type of RNA does it make?
tRNA; 5S rRNA, 7S RNA, and some snRNAs
Which nuclear RNA is insensitive to amanitin and what type of RNA does it make?
Which type of eukaryotic rRNA is the product of transcription of a different gene and which nuclear RNA makes it?
How does RNA polymerase know where to start transcription?
Promoter sequences, which differ between prokaryotes and eukaryotes, direct them.
3 sequence elements for most prokaryotic promoters
What type of nucleotide is the initiation site usually?
What makes the promoters used by RNA pol III in eukaryotes unique?
They usually start downstream of the startpoint.
What makes RNA pol II promoters unique?
There is a large diversity of them.
What sequence elements are common to RNA pol II's?
Affect the rate of initiation of transcription but are not actually considered promoter elements because they don't affect the accuracy of initiation of transcription
What is required for accurate initiation of transcription in prokaryotes? In fact, it is the only initiation factor needed in these organisms.
What's the function of the sigma factor?
Enables RNA polymerase holoenzyme to recognize and bind tightly to the promoter sequences
What does the sigma factor actually do?
It faciliates the opening or melting of the DNA double helix.
What is the mechanism of action of Rifampin?
It binds to the beta subunit of RNA polymerase when it's still in holoenzyme form.
By doing so, it inhibits the initiation (not elongation!) of transcription in bacteria.
Rifampin has no effect on eukaryotic nuclear RNA polymerases, thus making it an effective antiobiotic.
Sequences that cause termination transcription by forming a stable stem-loop structure through self-complementary sequences.
True/false: In factor-independent termination, there is a specific place where termination stops.
FALSE. RNA pol just falls off at some point on the uracil segment.
How does rho bind at unique termination sequences?
as a hexamer
What type of enzyme is rho?
What does it mean to say that rho is an ATPase?
Rho cleaves ATP in the process of termination, although the exact mechanism is unknown.
2 methods of termination in prokaryotes
How does RNA pol I terminate transcription?
How does RNA pol III terminate transcription?
by an unknown mechanism after the synthesis of a series of U's
How does RNA pol II terminate transcription?
We don't know.
Remove spacer RNA in the 30S precursor rRNA in prokaryotes.
In addition to the removal of the spacer sequences, some of the bases in the final rRNAs of prokaryotes are _____, which is necessary for the rRNAs to be functional.
Sequence common to all tRNAs
on 3' end
What's the name of the enzyme that adds the CCA sequence onto tRNAs that have been left without it after cleavage from the larger precursor transcript?
tRNA nucleotidyl transferase
Where does the synthesis and processing of 45S rRNA begin? What enzyme does this?
RNA pol I
precursor for eukaryotic rRNA
precursor for eukaryotic mRNA
2 functions of caps on eukaryotic mRNA
more efficient translation
more stable mRNA
A complex of proteins that recognizes and binds to the cleavage/polyadenylation signal
Directs an endonucleolytic cut of the RNA to a particular point downstream
cleavage and polyadenylation specificity factor
Joins the cleavage and polyadenylation specificity factor complex and, after the RNA is cut, catalyzes the polymeration of A residues onto the 3' end of the mRNA
poly A polymerase
When does polyadenylation occur?
After capping but before splicing
Function of polyadenylation
helps stabilize mRNA
the transcribed portions of the gene that are retained in the final mRNA product
exons (short for expressed)
What catalyzes splicing?
Function of snRNAs in the spliceosome
recognize the conserved sequences by introns and bringing together the RNA sequences into perfect alignment for splicing.
How does tRNA splicing work?
The splicing enzymes recognize characteristic structural features of the tRNA to recognize specific intron/exon junctions.