lecture 23 Flashcards
what is the general structure of a prokaryotic cells in the transcription
promoter
coding region (including termination)
termination
what happens in the initiation of prokaryotic?
RNA polymerase binds, unwinds and joins first 2 nucleotides.
-initiation of RNA synthesis DOES NOT
require a primer
what happens during the elongation of the prokaryotic
Complementary nucleotides
continue to be added during the elongation
process.
-localized DNA unwinding ahead of RNA
polymerase generates a “transcription
bubble”.
-transcription bubble moves with the
RNA polymerase and the unwound DNA
rewinds behind it.
what happens during the termination of the prokaryotic
Transcription stops when RNA polymerase reaches the “terminator” region of the gene.
-the newly-synthesized RNA together with
RNA polymerase are released
what are E. coli RNA polymerase
Core: a2 b b’ω
Holoenzyme: a2 b b’ ω s
what does a2 b b’ω do
Transcribes any DNA sequence
what does a2 b b’ω s do
the structure of the complete RNA polymerase, This structure is specific for transcribing genes
what is the role of alpha
a: (alpha subunit)-involved in the assembly of the tetrameric
core
what is the role of beta
b: (beta subunit) – contains the ribonucleoside triphosphate
(rNTP) binding site
what is the role of beta prime
b’: (beta-prime subunit- contains the DNA template binding
region
what is the role of omega
ω : (omega subunit)-it helps to stabilize the tetrameric (a2 b b’)
core
what is the role of sigma subunit
(sigma subunit) – it binds to the RNA polymerase tetrameric core and assists in the correct initiation of transcription specifically at the promoter region of the
prokaryotic gene. Sigma give the RNA polymerase specificity for the gene.
-Transcribes any DNA sequence (not gene specific)
-the structure of the complete RNA polymerase,
This structure is specific for transcribing genes
3. Transcription in Prokaryotes (cont’d)
E. coli RNA polymerase
what happens in the Initiation of transcription
recognition of the gene promoter region requires the intact RNA polymerase holoenzyme,
-Sigma factor recognizes and binds
to the -35 element in the promoter region, properly positioning the RNA polymerase to begin transcription
where does alpha factor binds
-35 position
what is -10 element
which due to its very A/T rich content, is prone to unwinding
where does the transcription initiates
Transcription initiates about 5-9 base pairs
down from the end of the -10 sequence
where is the +1 position
5’ end of the RNAis usually a purine (the +1
position
-35 and -10 elements are examples of ……………
-35 and -10 elements are examples of consensus sequences
what is the sequences of the -35
35 sequences has the consensus TTGACA which is important in unwinding DNA during transcriptional initiation.
what is the consequences of the -10
TATAAT
how many base pairs are in the Transcription bubble
-a localized region of unwinding of
~18 base pairs
Elongation occurs when Sigma factor is
released and RNA polymerase begins to move along the 3’ to 5’ DNA template strand.
-A localized region of unwinding called the
“transcription bubble” occurs as RNA
polymerase moves along the DNAtemplate.
where does positive supercolis form and which enzyme remove it ?
-Positive supercoils formed in the double-
stranded DNA ahead of the advancing RNA
polymerase are removed by topoisomerases
how does the termination happens
Common mechanism of transcription
termination in bacteria
-Weak H-bonding at U:A residues
allows mRNA release from DNA when
RNA polymerase pauses at terminator
what are the promoters in the eukaryotic transcription
There are specific promoter sequences for genes transcribed by RNA
polymerases I, II or III.
what is RNA polymerase II promoter consist of
It consists of a core promoter and a regulatory promoter that aid in positioning transcription proteins and RNA polymerase II to begin transcription
4. Transcription in eukaryotes (cont’d)
what do Y, R, N abbreviation mean
Abbreviations:
Y = pyrimidine, either C or T
R= purine, either A or G
N= any nucleotide, A,G,C orT
what is TFII
Transcription Factors of Pol. II (TFII A, B, D, E, F and H)
how is transcription in the eukaryotic
TFIID assembles first at the
TATAbox followed by the remaining general transcription factors (TFs) and Pol. II.
-this forms the “preinitiation complex” or PIC: that is sufficientto initiate transcription.
-More complex transcriptional regulation involves a multi-subunit complex called
“Mediator” that permits interactions with other activator proteins bound to
upstream/downstream regulatory regions or enhancer sequences.
what does core promoter do in the eukaryotic transcription
Core promoters assemble the transcriptional
machinery, but enhancer sequences determine how efficiently they transcribe, by
influencing them with cofactors (COFs)
what are TF, COF, PIC, GTF
TF= transcription factor; COF = transcription co-factor; PIC =pre- initiation complex;
GTF = general transcription factors
at this stage, many of the general
transcription factors remain
at the promoter providing for quick
re-initiation with a new Pol.II.
-this together with DNAunwinding,
ensures that the free RNA 3’-OH
terminus is available for new rNTP
addition.
how does transcription bubble generated
-an ~8 nucleotide “transcription bubble”
is generated by RNA:DNA binding.
what is alpha aminitin
potent inhibitor RNA polymerase
