Transcription Flashcards
(36 cards)
Central Dogma (fundamental law
the mechanism whereby inherited
information is used to create “actual
objects”, namely enzymes and structural
proteins.
Prokaryotic genes are composed of three sequence regions
1.Promoter region
2.RNA coding sequence
3.Terminator region
The region 5’ of the promoter sequence is called
d upstream sequences
The region 3’ of the terminator sequence is called
downstream sequence
Transcription is
e first stage in gene
expression and the principal step at which
it is controlled.
RNA polymerase is characterized by:
▪Search DNA for initiation site,
▪It unwinds a short stretch of double helical DNA to produce a single stranded DNA template,
▪It selects the correct ribonucleotide
and catalyzes the formation of a
phosphodiester bond,
▪It detects termination signals where
transcript ends.
Transcription initiation
RNA polymerase binds to the DNA of the
gene at a region called the promoter
A promoter contains
DNA sequences that let RNA polymerase, or its helper proteins attach to the DNA.
Promoters in bacteria (initiation) contains two important DNA sequences
the -10 and -35 elements.
Promoters in eukaryotes (initiation)
helper proteins called basal (general)
transcription factors bind to the promoter first.
Many eukaryotic promoters have a sequence called a
TATA box (25-30 nucleotides)
Role of TATA box (25-30 nucleotides),
much like that of the -10 element in bacteria.
tata box also contains lots of As and Ts, which make it
easy to pull the strands of DNA apart
The eukaryotic cell contains three types of distinct RNA polymerases
(A) RNA polymerase Ι transcribe genes that yield rRNAs.
(B) RNA polymerase ΙΙ transcribes protein-coding genes and results in the synthesis of mRNAs.
(C) RNA polymerase ΙΙΙ transcribe genes that yield tRNAs.
All of these three are complex multi-subunits enzymes
consisting of 8-14 subunits each.
RNA polymerase (RNAP) directs the
sequential binding of ribonucleotides
to the growing RNA chain in the 5’ - 3’ direction.
During elongation, RNA polymerase “walks”
along one strand of DNA
known as the TEMPLATE STRAND, in the 3’ to 5’ direction.
For each nucleotide in the template, RNA
polymerase
ADDS A MATCHING (complementary) RNA nucleotide to the 3’ end of the RNA strand.
The RNA transcript is nearly identical to the
non-template, or coding, strand of DNA.
However,
RNA strands have the base uracil
(U) in place of thymine (T), as well as a
slightly different sugar in the nucleotide
The process of ending transcription
is called termination
Termination happens once
the polymerase transcribes a sequence of DNA known as terminator
Terminators work in conjunction with RNA polymerase to
to loosen the association between RNA product and DNA template, so that RNA dissociate from RNA polymerase and DNA
Termination in bacteria
Rho-dependent termination (Extrinsic),
Rho-independent termination (Intrinsic),
In Rho-dependent termination (Extrinsic), the
RNA contains
a binding site for a protein called
Rho factor
A hairpin slows down polymerase allowing a
trailing protein called rho
to catch up and DISLODGE the polymerase from the template.