DNA transcription Flashcards
first suggestion that RNA
is derived from the transcription of DNA
Elliot Volkin and Lazarus Astrachan (1956)-
the base composition after infection was very similar
to the base composition in the T2 DNA,
except that the RNA
contained uracil instead of thymine.
found that proteins
are synthesized on ribosomes.
Matthew Meselson and François Jacob (1960)-
proposed that a certain
type of RNA acts as a genetic messenger (from the DNA to the
ribosome) to provide the information for protein synthesis.
François Jacob and Jacques Monod (1961)-
directs the synthesis of particular polypeptides.
messenger RNA
(mRNA),
Synthesis of RNA using DNA as a template
DNA TRANSCRIPTION
No primer needed, no proofreading activity
DNA TRANSCRIPTION
In eukaryotes, the polymerases synthesize specific RNA molecules:
- Pol I: rRNA
- Pol II: mRNA, lncRNA, miRNA, SnRNA
- Pol III: tRNA, 5S rRNA
DNA TRANSCRIPTION Enzyme:
DNA-dependent RNA polymerase
the overall process by which the information within a
gene is used to produce a functional product, such as a polypeptide.
Gene expression-
is the first step in gene expression
Transcription
provides a site for beginning transcription
Promoter-
specifies the end of transcription
Terminator-
to occur
within a defined location.
RNA synthesis
- type of DNA sequence that gets its name from the idea that it
“promotes” gene expression.
Promoter
directs the exact location for the initiation of
transcription.
promoter
The bases in a promoter sequence are numbered in relation to the
transcriptional start site
most of the ____ is labeled with negative numbers
promoter
- The sequence in the top DNA strand at the −35 site is
and
the one at the −10 site is
,
5′–TTGACA–3′
5′–TATAAT–3′.
TATAAT sequence is called the ____
who initially discovered it in 1975.
Pribnow box after David Pribnow,
___is complementary to the
template strand of DNA.
RNA transcript
opposite strand of DNA is the ___
nontemplate strand.
is also called the
coding strand, or sense strand, because its sequence is the same as
the transcribed mRNA
nontemplate strand
is also called the non-coding strand, or antisense strand.
template strand
controls the rate of transcription.
Transcription factors-
complementary to a
sequence in ribosomal RNA.
Ribosome-binding site (the Shine-Dalgarno sequence)
read as groups of
three nucleotides,
Codons-
which is very close to the ribosome-binding
site, is the start codon.
first codon,
signals the end of translation.
stop codon
Transcription
occurs in three
stages:
- Initiation
- Elongation
- Termination
the enzyme that interact with the DNA sequences and
synthesizes RNA.
RNA polymerase-
Is a recognition step
identifies the starting site for transcription when the DNA is in the
form of a double helix.
Initiation stage
the open promoter complex,
or the open complex.
Elongation stage
RNA polymerase and the newly made RNA transcript to dissociate
from the DNA.
Termination stage
eukaryotes :
* TATA or Hogness box, about –25 bp
* CAAT box, about –70 to 80 bp
prokaryotes:
* –35 sequence (TTGACA)
* Pribnow box (TATAAT), about –10 bp
eukaryotes :
* TATA or Hogness box, about –25 bp
* CAAT box, about –70 to 80 bp
prokaryotes:
* –35 sequence (TTGACA)
* Pribnow box (TATAAT), about –10 bp
In prokaryotes, the core enzyme is composed of five subunits, ____.
α2ββ′ω
important in the proper assembly of the holoenzyme
and in the process of binding to DNA.
Two α subunits
needed for binding to the DNA, and they carry out the
catalytic synthesis of RNA.
β and β′ subunits-
important for the proper assembly of the core
enzyme.
ω (omega) subunit-
The ___ is required to initiate transcription.
holoenzyme
- primary role is to recognize the promoter.
sigma σ factor
is a
structure contained in a σ-factor(sigma)
Helix-turn-helix motif-
within the protein
fit into the major groove of the DNA
Alpha (α) helices
- Local unwinding of the DNA continues in the 3’to 5’ direction
- RNA is synthesized in a 5′ to 3′ direction using nucleoside
triphosphates as precursors, releasing pyrophosphate each time
STEP 2: ELONGATION
is made during the elongation stage.
RNA transcript
the open complex formed by the action of, RNA polymerase is approximately __ bp long.
17
On average, the rate of RNA synthesis is about ___ nucleotides per
second.
43
always connects nucleotides in the 5′ to 3′ direction.
RNA polymerase
requires formation of a hairpin loop
requires ρ protein to release RNA from DNA
- ρ-independent:
- ρ-dependent:
Elongation of RNA continues until a termination signal is reached
STEP 3: TERMINATION
short RNA-DNA hybrid region is forced to separate,
Termination
an RNA-binding protein responsible for terminating
transcription, in a mechanism called
ρ (rho)- ρ-dependent termination.
does not require the involvement of
the ρ protein
ρ-independent
termination.
a site in the DNA encodes a
sequence in the RNA that acts as a recognition site for the binding of
the ρ protein
Rut site (for rho utilization site)-
binds to the RNA and moves in the direction of RNA
polymerase.
ρ protein
- Does not require the ρ protein
- One sequence promotes the formation of a stem-loop.
- The second sequence, which is downstream from the stem-loop, is a
uracil-rich sequence located at the 3′ end of the RNA.
ρ-INDEPENDENT TERMINATION (2 components)
___ are removed and ___ are spliced together
Introns, exons
RNA polymerase binds to DNA
promoter sequences
STEP 1: INITIATION
