This is an assignment prepared by me in 2022, when i was studying at Muhimbili College of Health and Allied Science(MUCOHAS)

1. DNA TRANSCRIPTION
IN CENTRAL DOGMA
GROUP PRESENTATION

2. ABOUT CENTRAL DOGMA
The idea of protein synthesis(Central Dogma) was firstly introduced by
Frances Crick in 1958,it is often known as the central dogma since it is
the most elementary concept required to understand all of biology. All
living things undergo the process of protein synthesis.
The three major players in central dogma are DNA, RNA and PROTEINS.
All living things require a blueprint, a recipe book to make various
essential molecules in our body such as proteins. In humans that
blueprint is found in the form of DNA which we inherit from our parents.
That DNA Is composed of four molecules known as bases which are
Adenine, Thymine, Guanine and Cytosine.

3. ABOUT CENTRAL DOGMA
For protein to be made information store in DNA must be first converted
into another form, a process known as TRANSCRIPTION converts the
genes from DNA to RNA, which is a very similar molecule. This is like
photocopying the original blueprint (DNA) onto different type of paper.
This is because the protein making machinery (Ribosome), can only
understand genetic information in the form of RNA.
Depending on what the gene codes for, the molecule in the process may
proceed onto becoming proteins or remains as RNA, which now serves
other important functions for the cell such as helping other RNA
molecules becoming proteins.

4. Central Dogma invloves two major
processes
It is called translation because the nucleotide sequence of mRNA
must be translated into completely different language of Amino
acids
TRNSCRIPTION
It is called transcription because it involves rewritting
or transcribing DNA sequence in a similar RNA
TRANSLATION
1
2

6. TRANSCRIPTION
1

7. TRANSCRIPTION
Transcription is the first step in gene expression, in which
information from a gene is used to construct a functional product,
a protein.
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.

8. TRANSCRIPTION 3 STEPS
INITIATION
The phase during which the first
nucleotides in the RNA chain are
synthesized ELONGATION
Regulated process in which an RNA
chain complementary to the template
strand of DNA is synthesized as RNA
polymerase moves along DNA.
TERMINATION
This is the process by which
transcription ending.

9. TRANSCRIPTION INITIATION
Transcription is catalyzed by the enzyme RNA polymerase, which
attaches itself and moves along the DNA molecule scanning until
recognizes a promoter sequence.
This part of DNA indicates the starting point of transcription, and
there may be multiple promoter sequences within DNA molecule.
Transcription factors are proteins that control the rate of
transcription, they too bind to the promoter sequence with RNA
polymerase.

10. RNA polymerase;
The main enzyme involved in transcription is RNA
polymerase, which uses a single stranded DNA template
to synthesize a complementary strand of RNA.
Specifically, RNA polymerase builds an RNA strand in
the 5' to 3' direction, adding each new nucleotide to the
3' end of the strand.
Three types of RNA polymerase in eukaryotic are;
i) pol I = responsible for rRNA
ii) pol II = responsible for mRNA
iii)pol III= responsible for tRNA

11. TRANSCRIPTION INITIATION Cont…
Once they (enzyme and factor) bound to the promoter
sequence, the enzyme (RNA polymerase) unwind the DNA
double helix. The unzipping exposes the bases on each of
the two DNA strands.
After unwinding the DNA strand the activated
phosphorylated ribonucleotides come to lie opposite of the
DNA template nitrogen base whereby A will be opposite to
T, U opposite A, G opposite C and C opposite G.

12. TRANSCRIPTION INITIATION Cont…
https://lab.concord.org/embeddable.html#interactives/sam/DNA-to-
proteins/2-modeling-transcription.json

13. TRANSCRIPTION ELONGATION
In elongation is where the formation of RNA chain occur
whereby;
One strand of DNA, acts as a template for RNA polymerase. As
it "reads" this template one base at a time, Polymerase builds
an RNA molecule out of complementary nucleotides, making a
chain that grows from 5' to 3’.
The RNA transcript carries the same information as the non-
template (coding) strand of DNA, but it contains the base uracil
(U) instead of thymine (T).

14. TRANSCRIPTION TERMINATION
The previous process (elongation) continues until the RNA
polymerase encounters a stop sequence. Those
Sequences called terminators and they signal that the
RNA transcript is complete. Once they are transcribed,
they cause the transcript to be released from the RNA
polymerase.
This process separates the enzyme (RNA polymerase) as
well as the newly built RNA strand.

15. TRANSCRIPTION TERMINATION Cont…
As soon as the RNA strand separates, the unwounded sense and
the antisense strands of DNA re-establish hydrogen bonds
between their complementary base pairs.
AND NOW THE DUPLEX NATURE (DOUBLE HELIX) IS RESTORED.

16. Post Transcription RNA processing
5‘ CAPPING
Also act as a
protective group
from 5’ to 3’
POLY-A tail
Makes RNA more
stable and prevents
its degradation
SPLICING
Allowing new
combination of
exons to be created

17. Post Transcription RNA processing cont….
5’ Capping:
The 5’ end of the RNA product of DNA transcription contains a free
triphosphate group since it was the first incorporated nucleotide in
the chain. So this capping process replaces the triphosphate group
with another structures called “CAP”.
The cap is added by the enzyme Guanyl transferase. This enzyme
catalyzes the reaction between 5’ end of the RNA transcript and a
Guanine triphosphate (GTP) molecule.
Once in a place, the cap plays a role in the ribosomal recognition of
messenger RNA during TRANSLATION.

18. THE POLYADENYLATION:
At the end of the opposite end of the transcript comes in the form of a string
adenine bases attached to the end of the synthesized RNA chain. This string
of adenine is called the “poly A tail”. The addition of the adenines is catalyzed
by the enzyme poly A polymerase, which recognizes the sequence AAUAAA
as a signal for the addition.
The reaction proceeds through mechanism similar to that used for the
addition of nucleotides during transcription.
The poly A is found in most of eukaryotic RNA transcript. It helps to confer
stability of the mRNA, aids in the export of mRNA to the cytosol and also
together with the 5’ cap structure it is involved in the formation of a
translation-competent ribonucleoprotein (RNP)
Post Transcription RNA processing cont….

19. Post Transcription RNA processing cont….
SPLICING:
Eukaryotic DNA transcription takes place In a cell’s nucleus and
produces what is called primary RNA transcript or pre messenger
RNA.
Before the products (mRNAs) transported into cytoplasm, they must
undergo modifications that allow them to become mature messenger
Ribonucleic Acid (mRNA).
Splicing is the name given the reaction that removes unnecessary
segments of the primary RNA transcript called introns, this is since
the matured mRNA contains only exons.

20. Diagram: Splicing

21. Post Trans.. RNA processing… Splicing: cont….
With the help of spliceosome, a mult-component protein, the
splicing reaction occurs. Spliceosome contains five small nuclear
ribonucleoproteins (snRNPs). They are called U1, U2, U4, U5 and
U6. each snRNP contains protein components that are critical for
the splicing reaction.
U1 binds directly to the 5’ splice site via complementary base
pairing, then it recruits U2, which forms a complex with branch
point A. U4 and U6 work in concert to make “pre-splicing
complex” and U5 helps to hold the exons in place between the
first and second steps in the splicing reaction.

22. Once the splicing reaction have occurred and the
exons have been rejoined to form mature mRNA, the
resulting mRNA is freed from the spliceosome
machinery, and now they met the requirement
qualifications to pass through nucleopores to the
cytosol for central dogma next step (TRANSLATION).

23. ***THE END***
THANKS FOR BEING WITH US AND GOD BLESS YOU

25. References:
 DMLS Molecular Biology notes 2022, prepared by Mr. John Kimbe.
 Editors Principles of Research Methodology, by Phyllis G. Supino • Jeffrey S. Borer
 Molecular & Cell biology for Dummies, by Rene Fester Kratz, PhD, Biology
Professor at Everett Communty College (ECC), Everett, Washington.
 Essential Cell Biology, 4th edition, by Bruce Alberts, Dennis Bray, Karen Hopkin, Alexander
Johnson, Julian Lewis, Keith Roberts, Peter Walter all are PhD holders in different health health science
corners and Martin Raff MD in cell biology
 https://is.muni.cz/do/med/mimsa/12840881/17898932/32049468/13_Transcription_Regulati
on.pdf
 https://www.khanacademy.org/science/ap-biology/gene-expression-and-
regulation/transcription-and-rna-processing/a/overview-of-transcription