Prokaryotic and eukaryotic transcription differ in several key ways. Prokaryotic transcription occurs in the cytoplasm and uses a single RNA polymerase to produce polycistronic mRNA, while eukaryotic transcription takes place in the nucleus using three RNA polymerases and produces monocistronic mRNA. Additionally, prokaryotic transcription and translation are coupled, while in eukaryotes they are not coupled and post-transcriptional processing occurs. Overall, both follow similar steps of initiation, elongation, and termination, but differ in their location, involved enzymes, and mRNA processing.

1. GENE EXPRESSION &
REGULATION-part I
Presented by Dr.SIBI P ITTIYAVIRAH,
PROFESSOR,
DIVISION OF PHARMACOLOGY
DEPARTMENT OF PHARMACEUTICAL
SCIENCES,CPAS,CHERUVANDOOR,KERALA,INDIA.

2. Genes
A gene is a part of DNA that codes for a
particular protein.
DNA is the information database of the cell
and exists within the cell nucleus. It carries
all the important genetic instructions that
produce proteins required by our cells.
2

3. Gene

4. Each gene carries a particular set of instructions,
which is usually in coded format, used for an
accurate function or for a distinct protein
Genes are first transcribed-mRNA- converted into
a polypeptide chain.
A polypeptide is then converted to a protein.
All the hidden codes inside our genes emerged -
physical traits, are known as gene expression.

6. Gene expression
Gene expression is the process by which
information from a gene is used in the synthesis of a
functional gene product that enables it to produce
end products, protein or non-coding RNA, and
ultimately affect a phenotype, as the final effect.

7. These products are often proteins,
but in non-protein-coding genes such as
transfer RNA (tRNA) and
small nuclear RNA (snRNA),
the product is a functional non-coding RNA.

8. tRNA or transfer RNA is a type of RNA, which helps in the synthesis of protein from
mRNA. tRNA functions as an adapter molecule during the translation process. It was
earlier known as soluble RNA or sRNA. As an adapter, it links the amino acids to nucleic
acids.
RNAs (Ribonucleic acids) are an essential component of all living cells. RNAs take
part in the protein synthesis.
There are three different types of RNAs present in a cell, namely- mRNA or
messenger RNA, rRNA or ribosomal RNA and tRNA or transfer RNA.
They are named according to the function they perform. Each of the three types of
RNAs performs unique functions and have different structures.

9. the amino acids to the ribosomes, which has to be added to the polypeptide chain
and rRNA forms ribosomes along with proteins.

10. ● Non-coding RNAs (ncRNAs) are RNA molecules transcribed from the
genome that do not encode proteins. Non-coding RNAs play a big
part in epigenetics regulation of gene expression in addition to their
roles at the transcriptional and post-transcriptional level.

11. Non coding RNA

12. Gene expression is summarized in the central dogma of
molecular biology first formulated by Francis Crick in
1958,
]
further developed in his 1970 article,
and expanded by the subsequent discoveries of reverse
transcription
RNA replication.

14. The process of gene expression is used by all known
life—eukaryotes (including multicellular organisms)
, prokaryotes (bacteria and archaea),
and utilized by viruses—to generate the macromolecular machinery
for life.

15. In genetics, gene expression is the most fundamental level at
which the genotype gives rise to the phenotype, i.e. observable
trait.
The genetic information stored in DNA represents the
genotype, whereas
the phenotype results from the "interpretation" of that
information. Such phenotypes are often expressed by the
synthesis of proteins that control the organism's structure and
development, or
that act as enzymes catalyzing specific metabolic pathways

16. All steps in the gene expression process
may be modulated (regulated), including
the transcription,
RNA splicing,
translation, and
post-translational modification of a
protein.

17. ● RNA splicing, in molecular biology, is a form of RNA processing in which a
newly made precursor messenger RNA (pre- mRNA) transcript is transformed
into a mature messenger RNA ( mRNA ).
●
During splicing, introns (Non-coding regions) are removed and exons (Coding
Regions) are joined together
● In splicing, some sections of the RNA transcript (introns) are removed,
and the remaining sections (exons) are stuck back together.
● Some genes can be alternatively spliced, leading to the production of
different mature mRNA molecules from the same initial transcript.
.

20. RNA splicing

21. Regulation of gene expression gives control
over the timing, location, and amount of a given
gene product (protein or ncRNA) present in a
cell and can have a profound effect on the
cellular structure and function.
Regulation of gene expression is the basis for
cellular differentiation,
development,
morphogenesis and
the versatility and
adaptability of any organism

22. Cellular differentiation is the process in which a cell changes from
one cell type to another.
Usually, the cell changes to a more specialized type.
Differentiation occurs numerous times during the development of
a multicellular organism as it changes from a simple zygote to a
complex system of tissues and cell types.

25. Gene regulation

26. Transcription, the synthesis of RNA from DNA.
Genetic information flows from DNA into protein,
the substance that gives an organism its form.
This flow of information occurs through the
sequential processes of transcription (DNA to
RNA) and translation (RNA to protein).
Transcription occurs when there is a need for a
particular gene product at a specific time or in a
specific tissue.

27. Mechanism-Transcription
1. Transcription- In this step, with the help of RNA
polymerase enzymes, the messenger RNA is
produced resulting in the processing of mRNA
molecule.

29. RNA POLYMERASE
In bacteria a single type of RNA polymerase is responsible for
the synthesis of all types of RNAs.( mRNA,r RNA and tRNA).
In eukaryotes 3 types of RNA polymerase I,II and III) are
present in nucleus.
RNA pol I synthesizes rRNA,PolII synthesizes mRNA and RNA
PolIII synthesizes t RNAs, 5S tRNA and an sn RNAs.
The prokaryotic RNA polymerase is pentameric .Only
holoenzyme can initiate gene transcription.

31. ● RNA polymerase is a holoenzyme that catalyzes the
synthesis reaction of RNA.
● This holoenzyme is necessary to construct RNA strands
from template strands of DNA that function as templates
during the transcription process.
● Its function is to add ribonucleotides at the 3-terminus
of a growing RNA molecule.

32. ●
Ribonucleic Acid (RNA) Polymerase (RNAP) enzyme is a
multi-subunit enzyme that applies its activity in the catalyzation of
the transcription process of RNA synthesized from a DNA template
.
Prokaryotic (Bacteria, viruses, archaea) organisms have a single type of
RNA polymerase that synthesizes all the subtypes of RNA,
eukaryotes (multicellular organisms) have 5 different types of RNA
polymerases which perform different functions in the synthesis of different
RNA molecules.

33. Stages of Transcription
● The process of transcription can be broadly categorised into 3 main stages:
initiation, elongation & termination.
● Transcription is catalysed by the enzyme RNA polymerase. It attaches to and
moves along the DNA molecule until it recognises a promoter sequence, which
indicates the starting point of transcription.
In DNA transcription, the DNA sequence of a gene is copied out (transcribed) in
order to make a molecule of RNA. It is the first step in the expression of the gene.
The process of DNA Transcription is done by the enzymes known as RNA
polymerases.
● Transcription takes place in the nucleus. It uses DNA as a template to make an
RNA (mRNA) molecule. During transcription, a strand of mRNA is made that is
complementary to a strand of DNA.

35. Transcription begins when RNA polymerase binds to a
promoter sequence near the beginning of a gene (directly or
through helper proteins).
RNA polymerase uses one of the DNA strands (the template
strand) as a template to make a new, complementary RNA
molecule.
Transcription ends in a process called termination. Termination
depends on sequences in the RNA, which signal that the
transcript is finished.

36. RNA polymerase is crucial because it carries out transcription, the
process of copying DNA (deoxyribonucleic acid, the genetic
material) into RNA (ribonucleic acid, a similar but more short-lived
molecule).
Transcription is an essential step in using the information from
genes in our DNA to make proteins. Proteins are the key molecules
that give cells structure and keep them running.

37. Transcription is the first step of gene expression. During this process, the
DNA sequence of a gene is copied into RNA.
Before transcription can take place, the DNA double helix must unwind near
the gene that is getting transcribed. The region of opened-up DNA is called a
transcription bubble.

38. transcription happens in the nucleus of human cells, while
translation happens in the cytosol.
Also, in eukaryotes, RNA molecules need to go through
special processing steps before translation.
That means translation can't start until transcription and RNA
processing are fully finished.

39. Gene transcription-video

40. ● Transcription is the process in which a DNA sequence is transcribed
into an RNA molecule with the help of enzyme RNA polymerase.
One of the DNA strands acts as a template to make a
complementary RNA strand. Where the transcription start and
terminate? The transcription starts at the 5′-end of the DNA
sequence.
● The RNA polymerase is the main enzyme involved in transcription. It uses
single-strand DNA to synthesize a complementary RNA strand. The
DNA-dependent RNA polymerase binds to the promoter and catalyses the
polymerization in the 5’ to 3’ direction on the template strand. Once it
reaches the terminator sequence, the process terminates and the newly
synthesised RNA strand is released.

41. Initiation
RNA polymerase attaches to the DNA molecule and moves along the DNA strand
until it recognises a promoter sequence. These are known as the transcription start
sites. The DNA double helix then unwinds and all the bases on each of the DNA
strands are exposed. This acts as a template for a new mRNA strand.
Elongation
Ribonucleotides are added to the template strand that enables the growth of mRNA
growth.
Termination
RNA polymerase encounters a terminator sequence and the transcription stops.
RNA polymerase then releases the DNA template.

42. RNA Processing
The transcribed RNA is known as the pre-mRNA. It is
processed further to convert it into mature RNA. RNA
processing include:
● Capping
● Polyadenylation
● Splicing

43. Capping
A methylated guanine cap is added to protect the mRNA. It involves:
● Addition of methylated guanine
● It occurs at 5′ end of mRNA transcript
● It protects the mRNA from degradation
Polyadenylation
The poly-A tail also protects the mRNA from degradation. It involves:
● The endonucleases cleave the mRNA at a specific sequence.
● The enzyme polyA polymerase facilitates the addition of several
adenine nucleotides.

44. Splicing
● The non-coding sequences, i.e., the introns are removed by
spliceosome excision.
● The coding sequences or the exons join together by ligation.
Thus several proteins can be made from a single pre-mRNA. A
mature mRNA is obtained at the end of transcription.
An RNA transcript is obtained as an end product of transcription.
It can form any type of RNA such as rRNA, mRNA, non-coding
RNA and tRNA. The prokaryotes form a polycistronic mRNA
whereas eukaryotes form a monocistronic mRNA.

48. To understand this topic better, let us take the example of the
Keratin genes.
Keratin is a protein that helps in the formation our hairs, nails,
and skin.
In most cases, these things grow at a continuous speed as our
hairs, nails, and skin get worn down over a period of time.
The production of excessive keratin could form many hairs on the
skin, dry and hard skin, thick and long nails.
To avoid this, it is necessary to regulate the expression of keratin
gene.

49. Prokaryotic and Eukaryotic Transcription
Regulation of gene occurs differently, depending on
the type of organisms- prokaryotic or eukaryotic
Eukaryotes refer to both multicellular and
unicellular organism like- animals, fungi, plants, and
protists possessing cells with nuclei and other
organelles present within the cell.
.

50. Prokaryotes are single-celled organism like bacteria
which do not have a nucleus.
Regulation of prokaryotic and eukaryotic transcription
is completely different as eukaryotes have a nucleus
but prokaryotes do not.

51. The key difference between prokaryotic and eukaryotic
transcription is that the prokaryotic transcription takes
place in the cytoplasm
while the eukaryotic transcription takes place inside the
nucleus.

52. When this sigma factor binds to the DNA promoter sequence resulting in the unwinding of
DNA double helix, initiation takes place. Using one of the DNA strands as a template,
RNA polymerase synthesizes the RNA strand moving along the DNA strand unwinding the
helix in the 5’ to 3’ direction.
Hence, during the elongation step, this RNA strand grows from 5′ to 3′ forming a short
hybrid with the DNA strand.
Once the termination sequence meets, elongation of the mRNA sequence ceases. In
prokaryotes,
there are two types of termination; factor-dependent termination and intrinsic termination.
Factor dependent termination needs Rho factor, and intrinsic termination happens when
the template contains a short GC rich sequence near the 3′ end after several uracil bases.

53. Prokaryotic Transcription
When this sigma factor binds to the DNA promoter sequence resulting in the unwinding of D

54. Eukaryotic transcription takes place in the nucleus. Similar to prokaryotic
transcription, eukaryotic transcription also occurs via four steps, i.e. binding,
initiation, elongation and termination. However, eukaryotic transcription is more
complex than the prokaryotic transcription.
In a eukaryotic cell, three different kinds of RNA polymerases are present; they are
namely, RNA pol I, II and III and they differ from their location and types of RNA they
synthesize. RNA polymerase binds with the DNA at the promoter region with the help
of transcriptional factors.

55. When the DNA helix unwinds into single strands, RNA
polymerase catalyzes the synthesis of mRNA sequence
from the template strand.
This RNA strand grows from 5′ to 3′ forming a short hybrid
with the DNA strand, and that is called elongation.
Elongation is ceased with the transcription of a special
sequence called a termination signal.
Termination is controlled by a variety of signals which vary
with the enzyme involved.

56. Eukaryotic Transcription

57. Moreover, the initial RNA sequence that results from the
transcription is a premature RNA sequence. It contains
junk sequences. Hence, prior to translation, some
modifications occur in order to produce mature mRNA.
These modifications include RNA splicing, 5’ capping, 3’
adenylation, etc.
Once the modifications happen, mRNA sequence travels
to the cytoplasm. Unlike in prokaryotes, eukaryotic
transcription does not occur simultaneously with the
translation.

58. Similarities Between Prokaryotic and Eukaryotic Transcription?
● Both prokaryotic and eukaryotic transcription follow the same
mechanism.
● Also, both have similar steps.
● At the end of both processes, an mRNA is produced.
● Furthermore, RNA polymerase catalyzes both transcription processes.
● Besides, both processes use DNA template to produce a mRNA
sequence.

59. Difference Between Prokaryotic and Eukaryotic
Transcription?
Prokaryotic transcription takes place in the cytoplasm. On the other
hand, eukaryotic transcription takes place in the nucleus. This is the
key difference between prokaryotic and eukaryotic transcription.
Furthermore, prokaryotic transcription produces polycistronic mRNA
while eukaryotic transcription produces monocistronic mRNA
. Thus, it is also a difference between prokaryotic and eukaryotic
transcription. Also, one more difference between prokaryotic and
eukaryotic transcription is that the prokaryotic transcription involves one
type of RNA polymerase while eukaryotic transcription involves three
types of RNA polymerases.

60. Moreover, another difference between prokaryotic and
eukaryotic transcription is that the transcription and
translation are coupled in prokaryotes while they are not
coupled in eukaryotes.
Furthermore, in prokaryotes, post-transcriptional
modifications are not taking place while in eukaryotes,
post-transcriptional modification occurs.
Thus, it is also a difference between prokaryotic and
eukaryotic transcription.

62. Prokaryotic vs Eukaryotic Transcription
Transcription is the first step of gene expression, which is followed by
translation. Though the transcription mechanism is the same in prokaryotes
and eukaryotes, there are several differences between them. The key
difference between prokaryotic and eukaryotic transcription is that the
prokaryotic transcription occurs in the cytoplasm while the eukaryotic
transcription occurs in the nucleus.

63. Furthermore, prokaryotic transcription involves only one RNA
polymerase while eukaryotic transcription involves three types
of RNA polymerases.
Moreover, the mRNA sequence of prokaryotes is polycistronic
while in eukaryotes, mRNA sequence is monocistronic.
Not only that, in eukaryotes, post-transcriptional modifications
occur while in prokaryotes, they do not occur.
This is the summary of the difference between prokaryotic and
eukaryotic transcription.