The document discusses DNA transcription. It describes the process of transcription, including initiation, elongation, and termination. It discusses RNA polymerase, promoters, and post-transcriptional modifications. Key differences between prokaryotic and eukaryotic transcription are highlighted. The document also briefly mentions reverse transcription and some drugs that inhibit transcription.

2. OUR Group Member
MD.Moshiur Rahman 07 (2047)
MD.Mahir Rahman 60 (2100)
Jahid hasan 29 (2069)
MD.Rabel 46 (2086)

3. Content
INTRODUCTION
Features of transcription
RNA polymerase
 DNA TRANSCRIPTION STAGES
 POST TRANSCRIPTION MODIFICATION
-5’ CAPPING
 REVERSE TRANSCRIPTION
 DRUGS INHIBITING TRANSCRIPTION

5. DNA Transcription
Transcription is the process by which the information in a
strand of DNA is copied into a new molecule of messenger RNA
(mRNA)
• All eukaryotic cells have five major classes of RNA: (rRNA),
(mRNA), (tRNA), snRNA and (miRNA).
• The first three are involved in protein synthesis, while the small
RNAs are involved in mRNA splicing and regulation of gene
expression.

6. Similarities between Replication and
Transcription
The processes of DNA and RNA synthesis are similar
in that they involve-
 The general steps of initiation, elongation, and
termination with 5' to 3' polarity;
 Large, multicomponent initiation complexes; and
 Adherence to Watson- Crick base-pairing rules.

7. Differences between replication and transcription

8. Features of transcription
• 1. Highly Selective –
This selectivity is due to signals embedded in the nucleotide sequence of
DNA.
 Specific sequences mark the beginning and the end of DNA segment
which is o be transcribed.
 This signal instruct the enzyme where to start and stop transcription,
when to start and how often to start.
2. Formation of Primary Transcripts –
Many of RNA transcripts are synthesized as precursors known as Primary
transcripts.
On modification and trimming they are converted into functional RNA.

9. RNA polymerase
RNA polymerases are large enzymes with multiple subunits,
even in simple organisms like bacteria. Humans and other
eukaryotes have three different kinds of RNA polymerase: I, II,
and III.
 Each one specializes in transcribing certain classes of genes.
Plants have an additional two kinds of RNA polymerase, IV and
V, which are involved in the synthesis of certain small RNAs.

10. RNA polymerase
• RNA polymerases are enzymes that transcribe DNA into RNA. Using a
DNA template, RNA polymerase builds a new RNA molecule through
base pairing. For instance, if there is a G in the DNA template, RNA
polymerase will add a C to the new, growing RNA strand.

11. Template strand
• The information in the template strand is read out in the 3' to 5'
direction
• The sequence of ribonucleotides in the RNA molecule is
complementary to the sequence of deoxy ribonucleotides in
template strand of the double-stranded DNA molecule.

12. Transcription unit and Primary transcript
A transcription unit is defined as that region of DNA that includes the
signals for transcription initiation, elongation, and termination
The RNA product, which is synthesized in the 5' to 3' direction, is the
primary transcript.
 In prokaryotes, this can represent the product of several contiguous
genes
 In mammalian cells, it usually represents the product of a single gene
The 5' terminals of the primary RNA transcript and the mature
cytoplasmic RNA are identical.
 The starting point of transcription corresponds to the 5' nucleotide of
the mRNA.

13. Transcription overview
• Transcription is the first step of gene expression During this
process, the DNA sequence of a gene is copied into RNA
• Transcription uses one of the two exposed DNA strands as a
template; this strand is called the template strand. The RNA
product is complementary to the template strand and is almost
identical to the other DNA strand, called the nontemplate (or
coding) strand.
• There is one important difference: in the newly made RNA, all of
the T nucleotides are replaced with U nucleotides.

14. Transcription

15. Prokaryotic transcription Steps of
RNA Synthesis
• The process of transcription of a typical
gene of E. Coli can be divided in to three
phases-
• i) Initiation
• ii) Elongation
• iii) Termination

16. Transcription initiation
To begin transcribing a gene, RNA polymerase binds
to the DNA of the gene at a region called the promoter. Basically, the
promoter tells the polymerase where to "sit down" on the DNA and
begin transcribing.

17. Promoters in bacteria
• A typical bacterial promoter contains two important DNA
sequences, the -10 and -35 elements.
• RNA polymerase recognizes and binds directly to these
sequences. The sequences position the polymerase in the right
spot to start transcribing a target gene, and they also make sure
it's pointing in the right direction.
• Basically, the rear part of the enzyme binds to the -35 element,
while the front part binds to the -10 element.RNA polymerase
can only bind to the promoter if it's pointing in a particular
direction.

18. Promoters in bacteria
The -10 and the -35 elements get their names because they come 35 and
10 nucleotides before the initiation site (+1+1+1plus, 1 in the DNA).
The minus signs just mean that they are before, not after, the initiation
site.

19. Elongation
• Once RNA polymerase is in position at the promoter, the
next step of transcription—elongation—can begin. Basically,
elongation is the stage when the RNA strand gets longer,.
• During elongation, RNA polymerase "walks" along one
strand of DNA, known as the template strand, in the 3' to 5'
direction. For each nucleotide in the template, RNA
polymerase adds a matching (complementary) RNA
nucleotide to the 3' end of the RNA strand.

20. Elongation
The RNA transcript is nearly identical to the non-template, or coding,
strand of DNA. However, RNA strands have the base uracil (U) in place of
thymine (T), as well as a slightly different sugar in the nucleotide. So, as
we can see in the diagram above, each T of the coding strand is replaced
with a U in the RNA transcript.

21. Termination of transcription
• There are two major termination strategies found in bacteria: Rho-dependent and Rho-
independent.
• In Rho-dependent termination, the RNA contains a binding site for a protein called Rho
factor. Rho factor binds to this sequence and starts "climbing" up the transcript towards
RNA polymerase.

22. Termination of transcription
• Rho-independent termination depends on specific
sequences in the DNA template strand.
• As the RNA polymerase approaches the end of the gene
being transcribed, it hits a region rich in C and G nucleotides.
The RNA transcribed from this region folds back on itself, and
the complementary C and G nucleotides bind together. The
result is a stable hairpin that causes the polymerase to stall.

23. Post Transcriptional Modification
• The primary transcript needs to be modified to become functional tRNAs, rRNAs
and mRNAs.
Post Transcriptional modifications include;
Splicing
 Addition of 5’ cap
Creation of Poly A tail
RNA Editing..

24. POST TRANSCRIPTION MODIFICATION
5’ capping
It is a 7-methylguanosine tri-phosphate cap structure at the
5' terminal of eukaryotic mRNA.
The cap structure is added to the 5' end of the newly
transcribed mRNA before it transport to cytoplasm.
 The 5' cap of the RNA transcript is required both for
efficient translation initiation and protection of the 5' end of
mRNA from attack by 5-'3' exonucleases.

25. Reverse Transcription
 It is the process of synthesis double stranded DNA from Single stranded RNA by reverse
transcriptase enzyme (RNA directed DNA polymerase).
 Reverse transcriptase common in
 HIV
 MMLV (Moloney Murine Leukemia Virus),
 AMV (Avian Myeloblastosis Virus)
 Reverse transcriptase enzyme includes two activity: DNA polymerase and RNAase H

26. DRUG Inhibiting DNA Transcription
• Rifampicin binds with Beta subunit of
prokaryotic RNA polymerase but not to
eukaryotic RNA polymerases.
Rifampicin use for the treatment of
tuberculosis and leprosy.
• Mitomycin used as anticancer drug
Intercalates with DNA strands
blocks transcription.

27. DRUG Inhibiting DNA Transcription
Alpha amanitin
The mechanism of action is that alpha amanitin
inhibits RNA polymerase –II at both the
initiation and elongation states of
transcription.
Actinomycin D- Actinomycins inhibit both
DNA synthesis and RNA synthesis by blocking
chain elongation. Actinomycins are used as
anti-cancer drugs

28. Application of DNA Transcription
The goal of transcription is to make a RNA copy of a
gene's DNA sequence.
 For a protein-coding gene, the RNA copy, or transcript,
carries the information needed to build a polypeptide
(protein or protein subunit).
 Eukaryotic transcripts need to go through some
processing steps before translation into proteins.