1. Molecular Biology – Transcription
Dr Anurag Yadav
MBBS, MD
Assistant Professor
Department of Biochemistry
Instagram page –biochem365
YouTube – Dr Biochem365
Email: dranurag.y.m@gmail.com
MNR MEDICAL COLLEGE & HOSPITAL

2. Content
• RNA
• RNA Transcription steps

4. • The conventional concept of central dogma of
life which is essence .
• DNA makes RNA makes Protein.

5. GENOME
• Total DNA contained in an organism or a cell is
regarded as the genome.
• Genomics: The study of structure and function
of genome.

6. TRANSCRIPTOME
• The RNA copies of the active protein coding
genes represent transcriptome.
• The Study of transcriptome that involves all
the RNA molecules made by a cell, tissue or an
organism is transcriptomics.

7. PROTEOME
• Study of proteome is proteomics.
• Metabolomics: the use of genome sequence
analysis for determining the capability of a
cell, tissue or an organism to synthesize small
molecules (metabolites) is metabolomics.

8. TRANSCRIPTION
• Transcription is a process in which ribonucleic
acid (RNA) is synthesized from DNA.
• The word gene refers to the functional unit of
the DNA.
• Genetic information stored in DNA is
expressed through RNA.

9. • One of two strand of DNA serves as a
template (non coding or antisense strand) and
produces working copies of RNA molecules.
• The other strand which does not participate in
transcription is referred to as coding strand or
sense strand or non-template strand.

11. TRANSCRIPTION IS SELECTIVE
• The entire molecule of DNA is not expressed
in transcription.
• RNAs are synthesized only for some selected
region of DNA.
• The identification of the specific region on
DNA is inbuilt.

12. • The product formed in transcription is referred
to as primary transcript.
• Most of the time they are inactive.
• Activated with alteration – post-
transcriptional modification. (Functional RNA
molecule)

13. TRANSCRIPTION IN PROKARYOTES
• RNA polymerase: DNA dependent RNA
polymerase – synthesizes all the RNAs.
• Complex holoenzyme – 5 polypeptide
subunits - 2α, 1β and 1β’ and one sigma(s)
factor.
• The enzyme without sigma factor is referred
to as core enzyme.

14. INVOLVES THREE DIFFERENT STAGES
Initiation
Elongation
Termination

16. 1. INITIATION
• RNA Polymerase to DNA : is Prerequisite.
• Promoter Region : Specific region on the DNA
where the enzyme binds.
• Two base sequence on the coding DNA strand.
• Sigma factor of RNA: recognise for initiation.

17. Pribnow Box (TATA Box):
• 6 nucleotide bases (TATAAT), located on
left side of 10 bases away (upstream from
starting point of transcription.
The ‘-35’ sequence:
• second recognition site in promoter
region of DNA. Contain TTGACA – located
35bases (Upstream) away from left side
from the site of transcription start.

20. 2. ELONGATION
• Promoter is recognised, sigma factor is
released and transcription proceeds.
• RNA synthesized from 5’ end to 3’ end
antiparallel to the DNA template.
• The sequence of Nucleotide bases is
complementary to template DNA strand.

21. RNA Polymerase:
• No primer is required.
• Does not possess endo or exonuclease
activity.
• Hence, there is no ability to repair the mistake
in the RNA synthesized.

23. 4. TERMINATION
•Rho (ρ) Dependent
termination
•Rho (ρ)
Independent
termination
Process
stops by
termination
signals

24. 1. Rho (ρ) Dependent termination
• ρ factor, bind to growing part of RNA or DNA.
• Acts as ATPase and terminated transcription
and release RNA.
• Also responsible for the dissociation of RNA
polymerase from DNA.

26. 2. Rho (ρ) Independent termination
• The termination in this case is brought about by
the formation of hairpins of newly synthesized
RNA.
• This occur due to presence of palindromes.
• Palindrome: is word that reads alike forward and
backwards.
– Eg: madam, rotor.

28. • Much more complicated.
• All the eukaryotic transcription are not clearly
known.
TRANSCRIPTION IN EUKARYOTES

29. RNA Polymerases
• Synthesis precursor for large
ribosomal RNAs
RNA
polymerase I
• Synthesize precursor for
mRNAs and small nuclear RNAs
RNA
polymerase II
• Formation of tRNAs and small
ribosomal RNAs
RNA
polymerase III

30. Promoter sites
Hogness box (TATA box)
• Located left about 25 nucleotides (Upstream).
CAAT Box
• between 70-80 nucleotides upstream from the start of
transcription.
These two will help RNA polymerase II to recognize
the requisite sequence of DNA for transcription.

32. INITIATION
CHROMATIN combining the promoter
sequence.
Binding of transcription factors (TFs) to
DNA sequences in the promoter region.
Stimulation of transcription by enhancers.

33. Transcription Factors
• They interact with promoter region
• They are 6 in number : TFIID, TFIIA, TFIIB,
TFIIF, TFIIE, TFIIH.

34. ENHANCER
• It increase gene expression by 100 folds.
• Binding of enhancer to transcription factors to
form activators.
• It is believed that chromatin forms a loop that
allows the promoter and enhancer to be close
together in space to facilitate transcription.

36. HETEROGENEOUS NUCLEAR RNA
(hnRNA)
• The primary mRNA transcript produced by
RNA polymerase II in eukaryotes is often
referred to as heterogeneous nuclear RNA
(hnRNA).
• This is then processed to produce mRNA
needed for protein synthesis.

37. POST-TRANSCRIPTIONAL
MODIFICATIONS
RNA produced during the transcription
are called primary transcript.
They undergo alterations
• Terminal base addition
• Base modifications
• Splicing etc.,

39. 1. The 5’ capping
• 5’ end of mRNA is capped with 7-
methylguanosine by unusual 5’ to 5’
triphosphate linkage.
• It is required for translation process.
• Stabilizing the structure of mRNA

40. 2. Poly-A tail
• Adenine nucleotide chain is added at 3’ end.
• Stabilize the mRNA

41. 3. Introns and their Removal
• Introns are intervening nucleotide sequence.
• They do not code for Proteins
• Exons of mRNA possess the genetic code for
protein synthesis.
• This removal of Introns is promoted by small
nuclear ribonucleo-protein particles (snRNPs).
• They are produced in association with small
nuclear RNA .

42. • Spliceosome : snRNP association with hnRNA
at exon-intron junction.
• This is than, mature RNA enters the cytosol.

46. Faulty splicing can cause diseases
• Performed with precision to produced the
functional mRNA.
• Faulty will lead to disease / disorders.
• Eg: β-thalassemia.
• Mutation resulting in nucleotide change at an
exon-intron junction.
• Result in diminished or lack of synthesis of β-
chain of hemoglobin.

48. REVERSE TRANSCRIPTION
• Retroviruses – possess RNA as genetic
material.
• Reverse transcriptase ( RNA dependent DNA
polymerase ) is responsible for the formation
of DNA from RNA.

49. • This DNA is complementary (cDNA) to viral
RNA and can be transmitted into host DNA.
• mRNA serve as template for synthesis of
double-stranded complementary.

51. Important Q
• Transcription in detail
• Post transcriptional modification RNA
• Inhibitors of transcription
• Hairpin
• Palindrome
• Spliceosome
• Reverse transcription