transcription is the process of RNA synthesis from DNA

1. TRANSCRIPTION
• It involves copying a gene's DNA sequence
to make an RNA molecule.
•Thus, genetic information stored in DNA is
expressed through RNA by RNA polymerase
enzyme or DNA dependent RNA Polymerase.
•One of the two strands of DNA acts as
template (non-coding or antisense strand)
and produces working copies of RNA
molecules.

2. TRANSCRIPTION CONTD..
•The product formed in transcription is referred
to as primary transcript which are mainly
inactive so they undergo post transcriptional
modifications (like splicing, terminal additions,
base modifications etc.) to produce active RNA
molecules.
TRANSCRIPTION IN PROKARYOTES:
• It involves three different stages :
Initiation, Elongation, Termination

3. 1. Initiation: The RNA Polymerase enzyme binds to the specific
site of DNA Known as ‘promoter region’. The Sigma factor of
RNA Polymerase recognizes the two base sequence on the
coding DNA strand.
• Pribnow box (TATA box) : Consists of 6 nucleotide bases
(TATAAT), located on the left side about 10 bases away
(upstream) from the starting point of transcription.
• The ‘-35’ sequence : This is the second recognition site . It
contains base sequence TTGACA, (located about 35 bass
away from the left side from the site of transcription start.

4. 2. ELONGATION:
•RNA is synthesized from 5’ end to 3’ end
antiparallel to DNA template.
•RNA polymerase utilizes ribonucleotide
triphosphates ( ATP, GTP, CTP and UTP) for the
formation of RNA.
•The sequence of bases in mRNA is
complementary to DNA except that RNA contains
U in place of T in DNA.

5. 3. TERMINATION
The process of termination stops by termination signals.
They are:
1. Rho (ρ) dependent termination : It binds to growing RNA or
weakly to DNA and terminates transcription.
2. Rho (ρ) independent termination : formation of hairpins of
newly synthesized RNA takes place.