All about transcription

2. TRANSCRIPTION AND ITS
REGULATION
SUPERVISED BY
DR. SHAH HASSAN.
PRESENTED BY KEHKASHAN SABIR.
BS CHEMISTRY
ISLAMIA COLLEGE UNIVERSITY

3. Transcription
TRANSCRIPTION IS THE FIRST STEP OF GENE EXPRESSION, IN
WHICH A PARTICULAR SEGMENT OF DNA IS COPIED INTO RNA
(ESPECIALLY MRNA) BY THE ENZYME RNA POLYMERASE.
OR
DNA TRANSCRIPTION IS THE PROCESS IN WHICH DNA IS COPIED
INTO RNA; AS A RESULT THE PROCESS CAN ALSO BE CALLED RNA
SYNTHESIS.

4. 1) CHAIN INITIATION
 During initiation, RNA Polymerase binds to the promotor region of the
gene.
 This is region where the majority of gene expression is controlled.
 Binding causes the DNA double helix to unwind and open.

5. 2) CHAIN ELONGATION
 During elongation, RNA polymerase slides along the template DNA
strand. As the complementary bases pair up.
 The RNA polymerase links nucleotides to the 3’ end of the growing RNA
molecule.

6. 3) CHAIN Termination
 As the RNA polymerase reaches the terminator region of the gene, the
mRNA transcript is complete.
 Then the RNA polymerase, DNA stand and mRNA transcript dissociate
from each other.

7. DNA TRANSCRIPTION

8. TRANSCRIPTION
FACTORS
 TRANSCRIPTION IS REGULATED BY PROTEINS CALLED
TRANSCRIPTION FACTORS.
 TRANSCRIPTION FACTOR IS A PROTEIN THAT PRODUCE IN
CYTOPLASM AND EVENTUALLY MIGRATED IN TO THE NUCLEUS
,WHERE IT INTERACT WITH DNA AND STARTS TRANSCRIPTION.
 T.F THAT BINDS TO A DNA IN A SEQUENCE SPECIFIC MANNER
TO REGULATE TRANSCRIPTION.

9. Transcriptional Regulation
 Transcriptional regulation is about controlling how often a given gene is
transcribed.
 Once an RNA polymerase starts to transcribe, it continues to transcribe
until reaches the end of the gene.
 Transcription initiation is regulated by additional proteins, known
as activators and repressors.

10. Enhancer/Activator
 An Enhancer : is a DNA sequence located upstream or downstream of the promoter
region.
• An activator: is a regulatory protein that binds to enhancer sequence.

11. Enhancer/Activator
• Activators contain:
• A DNA binding domain: a location in the protein binds to DNA (enhancer
sequence).
• A protein binding domain: a location in the protein that binds to the
transcription initiation complex.

13. Enhancer/Activator
• When an activator binds to the enhancer sequence away from the promoter,
DNA loops so that the activator is in contact with the initiation complex.
• The activator interacts with the transcription initiation complex and give
signal to RNA polymerase to start transcription.
• Gene is turned ON and mRNA is made.

14. Enhancer/Activator regulates the
initiation of transcription by turning
ON

15. Regulation of transcription initiation
Silencer/Repressor
 A silencer: is a DNA sequence located upstream or downstream of the promoter
region.
 A Repressor is a regulatory protein that binds to silencer sequence.

16. Silencer/Repressor
 Repressors contain:
• A DNA binding domain: a location in the protein binds to DNA (silencer
sequence).
• A protein binding domain: a location in the protein that binds to the
transcription initiation complex.

17. Silencer/Repressor
• When an repressor binds to silencer sequence away from the promoter,
DNA loops so that the repressor is in contact with the initiation complex.
• The repressor interacts with the transcription initiation complex and
prevents the initiation of transcription.
• No mRNA is made.

18. Silencer/Repressor

20. Genetic
code
 The set of DNA and RNA sequences that
 determine the amino acid sequences used in th
e synthesis of an organism's proteins.
 It is the biochemical basis of heredity and
nearly universal in all organisms.

21. The genetic code is highly
similar among all organisms
and can be expressed in a
simple table with 64 entries.

26. Anti codon
The anticodon region is
a sequence of three
bases that are
complementary to a
codon in the messenger
RNA.

28.  The start codon is the first codon of a messenger RNA
(mRNA) transcript translated by a ribosome. The start codon
always codes for methionine in eukaryotes and a modified Met
(fMet) in prokaryotes. The most common start codon is AUG.
Start codon 28

29. STOP CODON
 In the genetic code, a stop codon (or termination
codon) is a nucleotide triplet within messenger RNA
that signals a termination of translation.
 Proteins are based on polypeptides, which are unique
sequences of amino acids.

30. • The reading of mRNA is always in the same
direction 5’ to 3’ (the same way as
transcription and replication).
• The code is universal for all organisms.