The document summarizes DNA replication in three main points:
1) DNA replication involves the semi-conservative duplication of DNA in which each new DNA molecule contains one old and one new strand. It is facilitated by various enzymes and occurs through multiple steps.
2) Replication initiates at the origin of replication and proceeds bidirectionally, forming a replication fork. The leading strand is replicated continuously while the lagging strand forms discontinuous Okazaki fragments.
3) Key enzymes involved include DNA polymerases, helicase, primase, ligase, topoisomerases and single-strand binding proteins which help unwind, copy and join DNA strands for accurate duplication of genetic material.
Replication Introduction , DNA replicating Models , Meselson and Stahl Experiments , Circuler Model of DNA replication , Replication in Prokaryotes , Replication In Eukaryotes , Comparison Between Prokaryotes and Eukaryotes Replicaton and PCR (Polymerease Chain Reaction)
RNA Polymerase
Introduction
Purification
History
PRODUCTS OF RNAP
Messenger RNA
Non-coding RNA or "RNA genes
Transfer RNA
Ribosomal RNA
Micro RNA
Catalytic RNA (Ribozyme)
prokaryotic and eukaryotic
Transcription by RNA Polymerase
TYPES OF RNA POLYMERASE
Type I
Type II
Type III
Prokaryotic Transcription Unit
EXPRESSION OF A PROKARYOTIC GENE
Prokaryotic Polycistronic Message Codes for Several Different Proteins
Eukaryotic Transcription Unit
ENHANCERS AND SILENCERS
RESULT OF THE TRANSCRIPTION CYCLE
RNAP III TRANSCRIBES HUMAN MICRORNAS
RNAP I–specific subunits promote polymerase clustering to enhance the rRNA gene transcription cycle
RNAP II–TFIIB STRUCTURE AND MECHANISM OF TRANSCRIPTION INITIATION
FIVE CHECKPOINTS MAINTAINING THE FIDELITY OF TRANSCRIPTION BY RNAP IN STRUCTURAL AND ENERGETIC DETAILS
DNA replication is fundamental process occurring in all living organism to copy their DNA. The process is called replication in sense that each strand of dsDNA serve as template for reproduction of complementary strand.
Replication Introduction , DNA replicating Models , Meselson and Stahl Experiments , Circuler Model of DNA replication , Replication in Prokaryotes , Replication In Eukaryotes , Comparison Between Prokaryotes and Eukaryotes Replicaton and PCR (Polymerease Chain Reaction)
RNA Polymerase
Introduction
Purification
History
PRODUCTS OF RNAP
Messenger RNA
Non-coding RNA or "RNA genes
Transfer RNA
Ribosomal RNA
Micro RNA
Catalytic RNA (Ribozyme)
prokaryotic and eukaryotic
Transcription by RNA Polymerase
TYPES OF RNA POLYMERASE
Type I
Type II
Type III
Prokaryotic Transcription Unit
EXPRESSION OF A PROKARYOTIC GENE
Prokaryotic Polycistronic Message Codes for Several Different Proteins
Eukaryotic Transcription Unit
ENHANCERS AND SILENCERS
RESULT OF THE TRANSCRIPTION CYCLE
RNAP III TRANSCRIBES HUMAN MICRORNAS
RNAP I–specific subunits promote polymerase clustering to enhance the rRNA gene transcription cycle
RNAP II–TFIIB STRUCTURE AND MECHANISM OF TRANSCRIPTION INITIATION
FIVE CHECKPOINTS MAINTAINING THE FIDELITY OF TRANSCRIPTION BY RNAP IN STRUCTURAL AND ENERGETIC DETAILS
DNA replication is fundamental process occurring in all living organism to copy their DNA. The process is called replication in sense that each strand of dsDNA serve as template for reproduction of complementary strand.
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2. DNA replication is also known as semi conservative
replication.
It is the process by which DNA is essentially
doubled i.e makes its exact copies.
It is an important process that takes place within
the dividing cell.
DNA is copied during the S phase of interphase.
Replication is the process of formation of exact carbon
copies of a substance.
3.
4. DNA replication can occur by three possible
methods:
Conservative replication : The parent structure
remains intact. The replica is a completely new
structure.
Disruptive replication: The parent structure
fragments and two new structures are formed afresh.
Semiconservative replication : One half of the
parent structure passes into each replica and the
second half is built anew.
DNA structure proposed by Watson and Crick (1953)
was based on its semiconsevative replication.
5.
6. DNA replication is a complex multistep process that
require a number of enzymes , protein factors and ions.
ORIGIN OF REPLICATION:
Replication begins at a particular region of DNA,
characterized by primarily three types of structures:
I. Sites for binding of proteins mainly intiation and
auxillary proteins.
II. A characteristically AT rich region that is unwound
III. Sites & structural properties involved in regulating
initiation.
7. It is called origin of replication or ori.
Prokaryotes have single origin of replication while
eukaryotes have several of them.
DNA of prokaryotes functions as a single replicating
unit called ‘’replicon’’.
DNA of eukaryotes possess a number of replicons or
replicating units.
The use of vector for recombiant DNA procedure is
meant for providing origin of replication.
Replication proceeds on both sides from Ori, this is
called bidirectional replication.
Unidirectional replication is rare.
8.
9. ACTIVATION OF DEOXYRIBONUCLEOTIDES:
4 types of deoxyribonucleotides – dAMP, dGMP, dTMP,
dCMP.
With the help of energy , phosphate and enz.
phophorylase the nucleotides are changed in
triphosphate state i.e dATP, dGTP, dTTP, dCTP .
10. INITIATION:
Origin of replication is recoganized by recognition
complex.
It attracts enzymes.
Enzyme helicase unwinds the DNA helix and unzips
the two strands of DNA by breaking hydrogen bonds.
The separated strands become stabilized in this
condition with the help of Single strand binding
proteins or SSBPs.
Unwinding creates tension which is released by cutting
and resealing enzymes topoisomerases I &II.
11. Topoisomerase II of prokaryotes is also called gyrase.
It functions both as helicase and topoisomerase.
Unzipping creates a Y-shaped configuration called
replication fork, forms within the nucleus during DNA
replication.
It is created by helicases, which break the hydrogen
bond holding the two DNA strands together
The resulting structure has two branching “prongs”,
each made up of single strand DNA .
These two strands serve as the template for leading
and lagging strand , which will be created as DNA
polymerase matches complementary nucleotides to
the templates, the templates may be properly referred
to as the leading strand template and the lagging
12. strand template.
• DNA is always synthesized in 5’ to 3’ direction.
• Since the leading and lagging strand templates are
oriented in opposite directions at the replication
fork , a major issue is how to achieve synthesis of
new lagging strand DNA, whose direction of
synthesis is opposite to the direction of the
growing replication fork.
13.
14. The leading strand is the strand of new DNA
which is being synthesized in the same
direction as the growing replication fork.
The polymerase reads the leading strand
template and adds complementary nucleotides
to the new leading strand on continuous basis.
15. The lagging strand is the strand of new DNA
whose direction of synthesis is opposite to the
direction of the growing replication fork.
Because of its orientation , replication of the
lagging strand is more complicated as
compared to leading strand.
As a consequence, DNA polymerase on this
strand is seen to lag behind the other strand.
16. The lagging strand is synthesized in short ,
separated segments.
On the lagging strand template , a primase reads
the template DNA and initiates synthesis of a short
complementary RNA primer.
A DNA polymerase extends the primed segments,
forming okazaki fragments
The RNA primers are then removed and replaced
with DNA, and the fragments of DNA are joined
together by DNA ligase.
17. Okazaki fragments are small stretches of DNA with
1000-2000 base pairs in length.
Named after scientist Rejis Okazaki who
discovered them in 1968.
These fragments are synthesized by DNA
polymerase.
Okazaki fragments are joined together by enzyme
DNA ligase
18. A large number of enzymes are required for DNA
replication
The main enzyme which takes part in combining
deoxyribose nucleotides to form new DNA strands is
called DNA dependent DNA polymerase
The other enzymes required for DNA replication are-
primase, topoisomerase, helicase, single strand
binding proteins,DNA ligase etc.
19. These enzymes copy DNA sequences by using one
strand as a template.
The reaction catalysed by DNA polymerases s the
addition of deoxyribonucleotides to a DNA chain .
Prokaryotes have three types of DNA polymerases- I,
II, III. DNA polymerase I ( also called Kornberg
enzyme) is used in proof reading, whereas, DNA
polymerase II is a specialized repair enzyme. DNA
polymerase III actually takes part in replication.
Eukaryotes have 5 types of DNA polymerases.
20.
21. It is called DNA unwinding protein.
Binds to single stranded regions of DNA to prevent
premature annealing, to protect ss DNA from being
digested by nucleases.
To remove secondary structure from DNA to allow
other enzymes to function effectively upon it.
Major function is to prevent recoiling of DNA strands
after its unwinding by helicases.
22. It is strand of nucleic acid that serves as a starting point for
DNA synthesis.
DNA polymerases adds new nucleotides to existing strand
of DNA.
Replication starts at the 3’ end of the primer, and copies the
opposite strand.
PRIMASE:
It is a type of RNA polymerase which creates RNA primer.
RNA primer functions as 5’ end of the new strand( to be
synthesised).
23. Primase is of key importance because no known DNA
polymerases can initiate the synthesis of DNA strand
without an initial RNA or DNA primer.
DNA GYRASE
• Simply referred as gyrase.
• It relieves strain while ds DNA is being unwound by
helicase.
• This cause negative supercoiling of DNA.
• The ability of gyrase ( also topoisomerase) to relax
positive supercoiles allows superhelical tension ahead
of the polymerase to be released so that replication
can continue.
24.
25. They are often used to separate strands of DNA double
helix.
They are proteins which are involved in unwinding of
DNA molecule, to provide a ssDNA for replication ,
transcription and recombination.
TOPOISOMERASE
They are a group of enzymes which control
supercoiling of DNA thereby maintaining a
superhelical tension.
They are of two types – type I and type II
26. Responsible for connecting DNA segments during
replication, repair and recombination
They catalyze the formation of alpha-phosphodiester
bond between two DNA chains
This enzyme requires the free OH group at 3’ end of the
other DNA strand and phosphate group at 5’ end of
the other.
