it is a fundamental process in biology

2.  Gene transcription is a process by which RNA
is formed from DNA.
 It involves 3 steps- Initiation ,elongation and
termination.
 Materials for gene transcription are-
 RNA polymerase
 DNA template
 General transcription factors
 Specific sequence of DNA

3.  Initiation
 In prokaryote RNA pol enzyme directly binds
with the specific sequence of DNA. It is
called promotor. It has 2 important
sequence- -10 element(5’TATAAT3’) and -35
element(5’TTGACG3’).
 RNA pol binds to the promotor region to
unwind DNA strand and form transcription
bubble.
 It occurs because of the weak hydrogen bond
present between A and T bases.

5.  RNA strand gets longer by addition of new
nucleotides.
 RNA pol moves from 3’ to 5’ direction.RNA
nucleotide has 3 phosphate group attached
to it.
 Inner most phosphate reacts with 3’ hydroxyl
group of existing strand.
 A pyrophosphate is lost in this process.

7.  It involves 2 different pathways-rho
dependent and rho independent pathway.
 RHO DEPENDENT PATHWAY
 Rho factor is a hexamar composed for 6
identical subunits. It has helicase and ATP
hydrolysis activity.
 A specific sequence that present in DNA that
transcribe rho factor is called Rut site.
 Rho factor binds with rut site in RNA and
continues moving upto RNA pol. It catches
RNA pol and dissociates RNA strand from DNA
template.

8.  RHO INDEPENDENT PATHWAY
 It requires the formation of hairpin
structure.
 Termination sequence contains GU rich
region followed by t strech and it transcribed
to form poly U tail.
 Hairpin structure leads to the dissociation of
RNA pol, RNA strand and DNA template.

10.  INITIATION
 RNA pol does not directly bind with the
promoter region of DNA. It require general
transcription for proper binding.
 TF II D is the first general transcription factor
that binds with DNA. Ultimately RNA pol
binds to the general transcription factors and
form initiation complex.
 Transcription bubble is generated due to the
breakdown of AT rich sequence of promoter
region.

12.  It is same as in prokaryotes.

13.  CAPPING
 When the mRNA 25-30 nucleotide long 5’end
is modified by the addition of a guanine cap
with methyl (Ch3)group at N-7 position of
guanine.
 5’ cap function
 It protects the nasent pre –mRNA from
degradation by exonuclease.
 Essential role in cap dependent initiation of
protein synthesis.

14.  Cleavage of 5’ end triphosphate of the
transcript by triphosphatase.
 Addition of a GMP by guanyl transferase
providing the guanosine cap.
 RNA methyl transferase transfer methyl
group to the guanosine cap to yields 7
methyl guanosine cap that is to 5’ end of the
transcript
 Methylation of 2’ hydroxls of 1st several
bases.

16.  There is a specific sequence present near the
5’ end of DNA. It is called AAUAAA sequence.
 There is a GU rich sequence near the 3’ end.
 Clevage and polyadenylation specifity
factor(CPSF) binds to AAUAAA sequence.
 Cleavage stimulating factor(CSF) helps to
cleave the sequence. Clevage factor(CF) 1
and 2 associated with this protein.
 Poly a polymerase(PAP) builds a poly a tail on
3’ end of mRNA. Poly a polymerase binding
protein (PABP)enhances the rate of poly a
addition.

18.  It is essential for the removal of introns from
the newly formed mRNA.
 Introns are mainly composed of a 5’ GU rich
region ,a branching site (UACUAAC),a
polypyrimidine tract and 3’ splice site(AG).
 Splicing process is carried out by a large
complex called spliceosome. Each of them is
composed of 5 small nuclear RNA and a range
of associated proteins.