Transcription Flashcards
α2ββ’σ RNA polymerase ___________
holoenzyme
α2ββ’ Core polymerase
Synthesizes RNA but unable to bind to __________
promoters
σ Binds the holoenzyme to promoter ___________
sequence
ββ’ Both contribute to ___________ site
active
β’ Binds to _________ template
DNA
β Binds to ______ nucleotides
RNA
α Essential for assembly of _______
subunits
enzyme
RNA polymerase moves along the template strand, producing an RNA copy of the _____________ ___________ strand.
complementary, nontemplate
The RNA transcript is both transcribed and translated in the ______ direction.
5’→3’
The 5’ end of the transcript corresponds to the _________ end of the polypeptide
N-terminal
First step in initiation in prokaryotes
RNA polymerase holoenzyme binds to the promoter region and separates the DNA strands, creating an open promoter complex.
in the secod step of initiationThe first and second RNA nucleotides bind to the RNA polymerase and to the +1 and +2 bases, respectively, at the transcription start site. The two nucleotides are then linked by a __________
phosphodiester bond
In the third step of initiation, __________ ________ begins to move along the template strand, adding additional nucleotides to the growing RNA chain.
RNA polymerase
in prokaryotes, The RNA polymerase initiates the mRNA synthesis almost always with a __________.
purine
what subunit is released, which completes initiation?
sigma (σ)
Where is the transcription promotor region in a prokaryotic cell?
+1 start site
the -35 region and the -10 region on the promoter bind to which subunit of RNA polymerase holoenzyme in prokaryotic cells?
sigma σ
in elongation, the a2BB’ moves along the template strand synthesizing RNA to what end?
3’
In elongation, as the core polymerase moves along the DNA, the double helix is unwound and then what?
it is rewound behind the advancing polymerase
what is the error rate in the growing RNA chain with wrong nucleotides in the
RNA?
1 in 10,000
to prevent slowing transcription, what does the topiosomerase enzyme do?
it acts to remove DNA supercoils and relax the DNA ahead of the polymerase
T or F: elongation has a rate of 20 to 50 nucleotides per second.
True
termination of transcription occurs through two different types in prokaryotes
(1) Termination of transcription is determined by specific
sequences along the DNA called termination sites, or
(2) Termination of transcription occurs through binding of
a protein termination factor called rho (ρ).
in termination in prokaryotes, inverted repeat sequences result in what type of structure in RNA?
hairpin or stem-loop
rho factor (ρ) dependent termination unwinds the RNA:DNA hybrid behind the RNA polymerase and releases what?
the transcript
what does RNA polymerase I do? in eukaryotes
transcribes major ribosomal
RNA genes; located in the nucleolus
what does RNA polymerase II do? in eukaryotes
transcribes protein-coding
genes and therefore synthesizes mRNA
what does RNA Polymerase III do? in eukaryotes
transcribes tRNA genes,
5S rRNA genes, and genes of other small RNAs
are polymerase i, ii and iii used in prokaryotes?
NO. they are in eukaryotes
which rna polymerase is the biggest? in eukaryotes
RNA POLYMERASE I
In the core eukaryotic promoter, the TATA box binds to what subunit of general
transcription factor TFIID?
TBP
this leads to the binding of RNA polymerase II and other general transcription factors after what happens?
Binding of TBP
Genes that lack a TATA box can use what initiator element that includes the transcription start site to accurately initiate transcription?
(Inr)
what 2 effects does the Mediator complex (M) have on initiation and elongation? in eukaryotic cells.
The Mediator complex (M) binds to general transcription factors and RNA polymerase II
and thereby helps to bring initiation.
Once elongation begins, the
Mediator complex (M) dissociates from the RNAP and GTFs.
what DNA binding protein
-Consists of two perpendicular α-helices connected by a β-turn.
-The side chains of one α-helix fit into the major groove of the DNA
Helix-turn-helix motif
what DNA binding protein
Consists of two antiparallel β-strands followed by an α-helix.
Zn 2+ ions are bound to amino acid side chains.
The α-helix inserts into the major groove of the DNA
Zinc finger motif
what DNA binding protein
-Consists of α-helices from two different proteins that form a coiled coil.
-Extensions of the α-helices bind to the major groove
Leucine zipper motif
A “cap” derived from ____ is added to the 5’ end
GTP
Why is a DNA loop made?
to bring the enhancer-bound activator protein to the RNA polymerase
What does a cap do?
(1) prevents exonuclease digestion
(2) helps with the binding of the mRNA to ribosomes
What linkage does the exonuclease not recognize and cut out?
5’-5’ link
he addition of ____________ groups to the 5’ end of a transcript is also an
essential step in mRNA maturation.
methyl (CH3)
what link can the exonuclease see?
3’-5’
Poly(A) addition to a ___________by poly(A)
polymerase follows a poly(A) signal sequence
AAUAAA
3’ end
The additions of up to 200 _ residues help protect the 3’ end from exonuclease
A
Spliceosomes recognize __________ sequences at the 5’ exon/intron junction and the branch site.
conserved
mRNA splicing is carried out by spliceosomes, composed of several ______-protein
complexes called snRNPs
RNA
In the splicing reaction, a covalently closed loop of RNA, the________, is formed by the
covalent attachment of the 5’ end of an intron to the branch site A.
lariat
The lariat is formed by covalent attachments of what two ends?
the 5’ end of an intron to the branch site A
The lariat is formed by covalent attachments of what two ends?
the 5’ end of an intron to the branch site A
mRNA decay begins with the shortening of the poly(A) tail by a _________ enzyme.
deadenylase
A decapping enzyme removes the 5’ cap. The mRNA is then degraded from _____ ends by 5’ and 3’ exonucleases.
both
The initial rRNA transcripts of ___ are converted into smaller rRNAs of 18S, 5.8S, and 28S by the action of endo- and exonucleases.
45S
what does a topoisomerase do in elongation? (prokayrotes)
it relaxes the double helix so RNA polymerase can move in a straight line
polymerase i,ii and III are used in eukaryotes or prokaryotes?
eukaryotes
TATA boxes are involved in prokaryotic transcription or eukaryotic?
eukaryotic
make flashcards on page 18
CPSF
binds to AAUAAA
