1. TRANSCRIPTION
(SYNTHESIS OF mRNA)
Presented to: Dr.Mansha
Presented by: saman Rubi
Bsf1800666
Bs-zoo(5th-M)

2. TRANSCRIPTION:
I. The synthesis of mRNA from DNA is called transcription.
II. mRNA is synthesized in the nucleus by using the nucleotide
sequence of DNA as a template.
III. The mRNA directs the synthesis of proteins, which occurs in the
cytoplasm.

4. SENSE AND ANTISENSE STRAND:
• The strand from which the mRNA is
synthesized or which is used as a
template is known as the antisense or
template strand.
• The strand of DNA that has the same
sequence of nucleotide as the mRNA is
known as the coding or sense
template.

5. TRANSCRIPTION IN PROKARYOTES
 In prokaryotes, transcription occurs in
cytoplasm due to the absence of
nucleus.
 Both transcription and translation
occurs simultaneously.

6. PROKARYOTIC RNA POLYMERASE:
RNA polymerase is used which transcribes all the genes. The prokaryotic
RNA polymerase is a multiple-subunit protein of ~480kD.
• In E. coli, the polymerase is composed of five polypeptide subunits. These
subunits assemble every time a gene is transcribed, and they
disassemble once transcription is complete. The polymerase comprised
of all five subunits is called the holoenzyme.

9. 1-INITIATION:
As the holoezyme is attached to the DNA strand,the sigma factor helps in
the recognition of the promotor region.
Promotor region is the site at the dna strand from where transcription
starts.
As the RNA polymerase recognizes the promotor region,it forms a bond
with the dna strand.After this bond formation,DNA double helix get
unwound and form a transcriptional bubble.

11. RECOGNITION OF PROMOTER REGION:
• The promoter is the DNA sequence at which RNA
polymerase binds.
• The -35 region of TTGACA sequence is the recognition site.
• RNA polymerase firstly binds at this site of promoter region.
• The -10 region of TATAAT is the region at which a stable complex
of DNA and RNA-pol has been formed.

13. 2-ELONGATION
As the RNA polymerase moves on the DNA strand,the bond between the
sigma factor and the polymerase got dissociate and the polymerase pulls
and moves forward at the dna strand and keeps on the addition of
ribonucleotides at the newly forming RNA strand.
The rate of addition of nucleotide is 40 nucleotide/s in prokaryotes amd in
bacteria its rate is 50 nucleotide/s.

15. TERMINATION:
• Specific termination singals are found at the DNA strand.
• A-T are the termination singals.When the polymerase reaches to the
termination nucleotide signals,the HAIRPIN structure started to formed at
the RNA strand.
• The bond between the DNA and mRNA got weak and finally the mRNA got
separated from the DNA strand.

17. REFRENCES:
www.nature.com
www.researchgate.com
en.Wikipedia.org