TRANSCRIPTION Class XII Biology based on NCERT Text book

1. D R . R . K . U P A D H Y A Y
TRANSCRIPTION

2. Central Dogma

3. The process of copying genetic information from one strand of
the DNA into RNA is termed as transcription.
TRANSCRIPTION
DNA
RNA
DNA dependent DNA Polymerase

4. RNA Polymerase holoenzyme consists of
core enzyme and sigma factor.
https://golifescience.com/rna-polymerase/

5. NITROGENOUS BASES IN DNA and RNA
https://www.technologynetworks.com/genomics/articles/

6. TRANSCRIPTION UNIT
 TEMPLATE STRAND
 CODING STRAND
 PROMOTOR
 STRUCTURAL GENE
 TERMINATOR

7. TEMPLATE & CODING STRAND
 3'-ATGCATGCATGCATGCATGCATGC-5' Template Strand
5’ 3’
(direction of synthesis of mRNA on template strand)
 5'-TACGTACGTACGTACGTACGTACG-3' Coding Strand
 SYNTHESIS OCCUR IN 5’ TO 3’ DIRECTION

8. CISTRON
The functional unit of gene that code polypeptide
Monocistronic: (mostly in eukaryotes): one gene
for one polypeptide
Polycistronic: (mostly in bacteria, chloroplast,
m. RNA ): different genes for different polypeptides

9. STEPS IN TRANSCRIPTION
 INITIATION
 ELONGATION
 TERMINATION
 NO PRIMER IS REQUIRED
 NTPs – ATP, GTP, CTP, UTP

10. INITIATION
 Sigma factor recognises the promotor site along with
RNA polymerase.
 RNA polymerase binds on promotor region.
 RNA polymerase unwinds DNA helix in structural gene
region (Transcriptional bubble)

11. https://www.khanacademy

12. ELONGATION
 RNA polymerase added NTPs of A, G, C and U as per
complementary base pair.
 A of DNA paired with U
 G of DNA paired with C
 New synthesis occur on template region of DNA (non
coding sequence).

13. https://www.khanacademy

14. TERMINATION
 When synthesis of RNA completed in structural
region, the rho factor dissociates RNA Polymerase
from DNA and transcription stops.

15. https://www.khanacademy
Rho factor is an ATP dependent DNA- RNA helicase)

16. POST TRANSCRIPTIONAL MODIFICATION
Conversion OF hn RNA (heterogeneous nuclear RNA)
into mature RNA
Methods:
SPLICING
5’ CAPPING
3’ TAILING

17. SPLICING
 REMOVAL OF INTRONS
 LIGATION OF EXONS
https://bio.libretexts.org/

18. 5’ CAPPING
 addition of methyl
group on 5 ’ end
guanine residue
 it protects the
transcript from being
broken down.
 It also helps the
ribosome attach to
the mRNA and start
reading it to make a
protein.

19. 3’ TAILING
 Polyadenylation is the addition of a poly(A) tail to a
AT 3’ end of hnRNA.

20. ONLY ONE STRAND OF DNA COPIED ???????
If both strands were used, the two RNA molecules would be complementary to
each other and form double-stranded RNA (dsRNA). dsRNA can't be translated
into proteins, so the transcription process would be futile.
If both strands were used, ribosomal proteins wouldn't be able to access promoter
regions, where they read the nitrogenous bases and transform them into keys to
position amino acids to create proteins.
RNAs are single-stranded, while DNA is double-stranded and needs two strands
for stabilization

21. THANK YOU
Source: NCERT text book, google images.