The document discusses the processes of transcription and post-transcriptional modification in RNA synthesis. It describes the roles of different types of RNA (mRNA, rRNA, tRNA) and details the stages of transcription such as initiation, elongation, and termination, as well as the modifications that occur in eukaryotic cells. Key differences between prokaryotic and eukaryotic transcription are highlighted, including the necessity for processing hnRNA into mature mRNA in eukaryotes.

1. Transcription and post-
transcriptional modification
by Abhishek Dahal

2.  rRNA: ribosomal RNA
 Major component of ribosomes
 tRNA: transfer RNA
 Carries amino acids to mRNA
 An interpreter in translation
 mRNA: messenger RNA
 Encodes genetic info from DNA and convey it to
the ribosomes, where the info is translated into
amino acid sequences

3. Transcription
 Process in which RNA is synthesized from DNA.
 DNA expresses through RNA
 1st
product of the RNA formed is called
TRANSCRIPT which is further altered to
produce functionally active RNA molecules.
 Synthesis of RNA occurs in 5´→3´ direction
 Nucleotides ATP,GTP,CTP,UTP are necessary
 Each nucleotide pairs with the complementary
nucleotide on the DNA template.

4. Stages of Transcription
 Promoter Recognition
 Chain Initiation
 Chain Elongation
 Chain Termination

5. promoter recognition
 Transcription factors bind to promoter seque
.
 Then, RNA polymerase denatures a
small segment of the DNA.
 Promoter region which consist of "TATA
box" and "-35 sequence" where
Transcription (sigma σ ) factor of
polymerase enzyme act.

6. Transcription: chain initiation
 Chain initiation:
 RNA polymerase locally denatures the DNA.
 RNA polymerase does not require a primer.
 The first 8 or 9 bases of the transcript are
linked. Transcription factors(sigma) are
released, and the polymerase leaves the
promoter region.

7. Transcription: chain
elongation
 Chain elongation:
 RNA polymerase moves along the
transcription unit of DNA strand.
 The new RNA molecule (primary
transcript) forms a short RNA-DNA
hybrid molecule with the DNA template.

8. Transcription: chain
termination
 Rho(Ƥ) dependent termination : here
Rho factor binds to the RNA or Weakly
to DNA causing Polymerase to release
and mRNA is formed.
 Rho(Ƥ) independent termination via a
molecule called as Philandromes that
can form a hairpin loop and release of
mRNA and polymerase occurs.

10. All have the same mechanism of action.
Recognize different type of promoters.
Eukaryote cells
Polymerase I produces most of the rRNAs
Polymerase II produces most of the mRNAs
Polymerase III produces small RNAs such as tRNA and 5 S RNA.

11. Post transcriptional modification
 Prokaryotes: mRNA transcribed directly from DNA
template and used immediately in protein synthesis
 Eukaryotes: primary transcript (hnRNA) must be
processed to produce the mRNA (active form).
 It occurs in nucleas of cell.

12.  4 process
 End modification:
 5´-a 7 methyl guanosine cap is added
 3´- a poly adenosine(poly A) tail is added
 These capping and tail addition stabilises
the RNA which is also required for
translation.

13.  Splicing
 Noncoding sequences (introns) are
removed
 Coding sequences (exons) spliced
together
 The removal is achieved by Small
nuclear ribonuclear protein (SnRNP).
 Mutations at the splice sites can cause
disease

Thalassemia • Breast cancer (BRCA 1)

14. mRNA is edited by
splicing

15.  Cutting:- here pieces of RNA are cut
which are not required( trimming).
 Chemical Modification:- new
chemical group are added and RNA is
modified into active form.

16. Modification of hnRNA
A cap is added at the 5’ end (cap sidt)
Poly-A tail added to the 3” end.
Introns are removed by a process called splicing to produce the mature mRNA.

18. Eukaryotic transcription and translation are separated in space and time
Prokaryotes
Eukaryotes
exons introns
nucleus
cytosol
translation
translation
transcription
DNA
transcription
nuclear export
splicing
pre-mRNA
mRNA
processing