This document summarizes the process of transcription in both eukaryotes and prokaryotes. It discusses the importance of transcription in using DNA to make proteins. The key steps in transcription are initiation, elongation, and termination. In initiation, RNA polymerase binds to the promoter region and unwinds the DNA. Elongation involves RNA polymerase synthesizing mRNA using one DNA strand as a template. Termination occurs when RNA polymerase reaches a terminator sequence and releases the mRNA. The document contrasts transcription between eukaryotes and prokaryotes, noting differences such as transcription occurring in the nucleus versus cytoplasm and the number of RNA polymerases involved.

2. Transcription
Presented By: Zarqa Chaudhary and Zunaira
Presented To: Mam Saba

3. Contents:
• Introduction
• Importance of Transcription
• Features of Transcription
• Role of Strands
• Enzymes and factors involve in Transcription
• Up stream & Down stream of strands
• Transcription in Eukaryotes and Prokaryotes
• Steps involved in Transcription
• Transcription in Eukaryotes
• Transcription in Prokaryotes

4. Introduction
• Transcription is the process of copying a segment of DNA into RNA.
• The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA
(mRNA). Other segments of DNA are copied into RNA molecules called non-coding RNAs (ncRNAs).

5. Importance of Transcription
• Transcription is an essential step in using the information from genes in our DNA to
make proteins.
• Proteins are the key molecules that give cells structure and keep them running.
• DNA can’t leave the nucleus so mRNA has to take the instructions from the DNA to
ribosomes

6. Features of Transcription

7. Conti…

8. Role of Strands:
• During Transcription only one strand of DNA is used as template.
• The other strand is called as non-template or coding strand.

10. Enzymes and factors involve in Transcription
• Transcription is carried out by an enzyme called RNA polymerase and a number of
accessory proteins called transcription factors.
• What enzymes are involved in transcription and translation? During transcription, the
enzyme RNA polymerase uses DNA as a template to produce a pre-mRNA transcript.

11. Conti…
Prokaryotes
• In Prokaryotes only one type of RNA
polymerase is used
Eukaryotes
• In Eukaryotes at least three types of RNA
polymerase is used
 RNA polymerase I
 RNA polymerase II
 RNA polymerase III

12. Up stream & Down stream of strands
RNA polymerase move 3’ to 5’ strands of DNA and synthesis in to 5’ to 3’ strands.
 Sequences on 5’ side called up stream
 Sequences on 3’ side called down stream

13. Transcription in Eukaryotes and Prokaryotes
Eukaryotes
• Transcription occurs in nucleus and
mitochondria .
• Here additional factors for RNA polymerase to
bind the DNA then these proteins called
general transcription factors
prokaryotes
• Transcription occurs in cytoplasm.
• A protein sub-unit called sigma bind to core
RNA polymerase.
• It forms RNA polymerase holoenzyme.
Holoenzyme binds promotor to initiate
transcription

14. Steps involved in Transcription
There are three major steps involved in Transcription of eukaryotes and prokaryotes:
1. Initiation
2. Elongation
3. Termination

15. Transcription in Eukaryotes
1. Initiation
The initiation of transcription requires special type of DNA sequence called a promoter . The promoter
tells the RNA polymerase where to start transcription . One element of the core promoter is called
TATA box. Eukaryotic also use enhancer sequence , it increases the efficiency of transcription initiation
of gene .
In the nucleus , RNA polymerase recognize the recognition sites causing it to bind to the promoter
(the start of the gene) . The RNA polymerase then separate the DNA into single strands so the
template strand can be read in the 3’ to 5’ direction.

17. Conti…
2. Elongation
Pre mRNA nucleotides are quickly paired with their complementary basis which corresponds with the
template strand of DNA . The pre mRNA moves in the 5’ to 3’ direction while the template strand of
DNA moves oppositely from the 3’ to 5’ direction . Pre mRNA does not contain thymine instead of
uracil is used as the complementary base for adenine .

19. Conti…
3. Termination
When the RNA polymerase reaches the terminator its signal the RNA polymerase to stop and release from the
DNA . Once separated the two DNA strands come back together and reform the double helix . The newly form pre
mRNA molecules is then released.

21. Prokaryotic Transcription

23. Conti…
Upstream:
The -10 sequence has to consensus TATAAT because this sequence was discovered by Pribnow, it is also
known as Pribnow box it is also an important recognition site that interact with sigma factor of RNA
polymerase.
Downstream:
-35 sequence has the consensus TTGACA and is important in DNA unwinding during transcriptional
initiation.

25. Conti…
Elongation:
Elongation in Prokaryotes The transcription elongation phase begins with the release of the σ subunit
from the polymerase. The dissociation of σ allows the core RNA polymerase enzyme to proceed along
the DNA template, synthesizing mRNA in the 5′ to 3′ direction at a rate of approximately 40 nucleotides
per second.

26. Transcription Bubble
• A transcription bubble is a molecular structure formed during DNA transcription when a
limited portion of the DNA double strand is unwound .
• The size of a transcription bubble ranges from 12-14 base pairs.

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