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DNA Replication in Prokaryotes
(ASSIGNMENT # 01 SEMESTER spring-2021)
Submission Date (March 20, 2021)
BY
Muhammad Hamza Saeed
ROLL # 19014107-015
ZOO-103(Principles of Animal Life-II)
BS (C)
Submitted to Dr.Akash Raza
Department of Chemistry
UNIVERSITY OF GUJRAT
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TABLE OF CONTENTS
PageNumbers Contents
3 Introduction
3
Replication process in Prokaryotes
4
DNA Replication in Prokaryotes
4 Three Principle kinds of Polymerases
5 Process of DNA replication summarized
6 Enzymes in prokaryotic DNA replication
6 References
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Introduction
DNA replication, the reason for natural legacy, is a key interaction happening altogether living
creatures to duplicate their DNA.In the cycle of "replication" each strand of the first double-
abandoned DNA molecule fills in as format for the proliferation of the correlative strand.Two
indistinguishable DNA molecules have been delivered from a solitary double-abandoned DNA
molecule..
Replication process in Prokaryotes
DNA replication includes:
Initiation – replication begins at an origin of replication
Elongation – new strands of DNA are synthesized by DNA polymerase
Termination – replication is terminated differently in prokaryotes and eukaryotes.
DNA Replication in Prokaryotes
Origins of Replication
Incidentally, there are explicit nucleotide
groupings called origins of replication where
replication starts. E. coli has a solitary birthplace
of replication on its one chromosome, as do most
prokaryotes.The beginning of replication is
roughly 245 base combines long and is rich in AT
groupings. This succession of base sets is
perceived by specific proteins that tight spot to
this site. A compound called helicase loosens up
the DNA by breaking the hydrogen connections
between the nitrogenous base sets. ATP
hydrolysis is needed for this interaction since it
requires energy. As the DNA opens up, Y-molded
constructions called replication forks are shaped.Two replication forks are framed at the
beginning of replication and these get expanded bi-directionally as replication proceeds. Single-
strand restricting proteins coat the single strands of DNA close to the replication fork to keep the
single-stranded DNA from twisting once more into a double helix.
Significant Catalyst
The following significant catalyst is DNA polymerase III, otherwise called DNA pol III, which
adds nucleotides individually to the developing DNA chain.The expansion of nucleotides
requires energy; this energy is gotten from the nucleotides that have three phosphates appended
to them. ATP primarily is an adenine nucleotide which has three phosphate bunches appended;
severing the third phosphate discharges energy. Notwithstanding ATP, there are likewise TTP,
CTP, and GTP. Every one of these is comprised of the relating nucleotide with three phosphates
appended. At the point when the connection between the phosphates is broken, the energy
Figure 1 DNA replication in prokaryotes, which
have one circular chromosome.
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delivered is utilized to shape the phosphodiester connection between the approaching nucleotide
and the current chain.
Three Principle kinds of Polymerases
in prokaryotes, three principle kinds of polymerases are known: DNA pol I, DNA pol II, and
DNA pol III. DNA pol III is the enzyme needed for DNA blend; DNA pol I is utilized later all
the while and DNA pol II is utilized basically needed for fix (this is another bothering illustration
of naming that was done dependent on the request for disclosure as opposed to a request that
makes sense).
DNA Polymerase
DNA polymerase can add nucleotides simply in the 5′ to 3′ bearing (another DNA strand can be
just reached out toward this path). It requires a free 3′-Goodness gathering (situated on the sugar)
to which it can add the following nucleotide by shaping a phosphodiester connection between the
3′-Gracious end and the 5′ phosphate of the following nucleotide. This basically implies that it
can't add nucleotides if a free 3′-Goodness bunch isn't accessible. At that point how can it add the
principal nucleotide? The issue is addressed with the assistance of a preliminary that gives the
free 3′-Goodness end. Another enzyme, RNA primase, blends a RNA groundwork that is around
five to ten nucleotides in length and corresponding to the DNA. RNA primase doesn't need a free
3′-Gracious gathering. Since this arrangement makes preparations amalgamation, it is properly
called the preliminary. DNA polymerase would now be able to broaden this RNA groundwork,
adding nucleotides individually that are integral to the format strand.
Figure 2
A replication fork is framed when helicase isolates the DNA strands at the root of replication.
The DNA will in general turn out to be all the more exceptionally curled in front of the
replication fork. Topoisomerase breaks and changes DNA's phosphate spine in front of the
replication fork, along these lines alleviating the pressing factor that outcomes from this
supercoiling. Single-strand binding proteins tie to the single-stranded DNA to keep the helix
from re-shaping. Primase integrates a RNA preliminary. DNA polymerase III uses this
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preliminary to orchestrate the girl DNA strand. On the main strand, DNA is blended consistently,
while on the slacking strand, DNA is orchestrated in short stretches called Okazaki pieces. DNA
polymerase I replaces the RNA groundwork with DNA. DNA ligase seals the holes between the
Okazaki pieces, joining the parts into a solitary DNA atom. (credit: change of work by Mariana
Ruiz Villareal).
Replication Fork
The replication fork moves at the pace of 1000 nucleotides each second. DNA polymerase can
just reach out in the 5′ to 3′ heading, which represents a slight issue at the replication fork. As we
probably are aware, the DNA double helix is hostile to resemble; that is, one strand is in the 5′ to
3′ heading and the other is situated in the 3′ to 5′ course. One strand, which is reciprocal to the 3′
to 5′ parental DNA strand, is integrated persistently towards the replication fork on the grounds
that the polymerase can add nucleotides toward this path. This ceaselessly combined strand is
known as the main strand. The other strand, correlative to the 5′ to 3′ parental DNA, is expanded
away from the replication fork, in little parts known as Okazaki pieces, each requiring a
groundwork to begin the blend. Okazaki parts are named after the Japanese researcher who
originally found them. The strand with the Okazaki sections is known as the slacking strand.
The main strand can be reached out by one preliminary alone, though the slacking strand needs
another introduction for every one of the short Okazaki pieces.
Sliding Clamp
The general bearing of the slacking strand will be 3′ to 5′, and that of the main strand 5′ to 3′. A
protein called the sliding clamp holds the DNA polymerase set up as it keeps on adding
nucleotides. The sliding clamp is a ring-formed protein that ties to the DNA and holds the
polymerase set up. Topoisomerase forestalls the over-twisting of the DNA double helix in front
of the replication fork as the DNA is opening up; it does as such by causing transitory scratches
in the DNA helix and afterward resealing it. As union continues, the RNA groundworks are
supplanted by DNA pol I, what separates the RNA and fills the holes with DNA nucleotides. The
scratches that stay between the recently integrated DNA (that supplanted the RNA groundwork)
and the recently combined DNA are fixed by the enzyme DNA ligase that catalyzes the
arrangement of phosphodiester linkage between the 3′-Goodness end of one nucleotide and the 5′
phosphate end of the other section.
The process of DNA replication can be summarized as follows:
1. DNA unwinds at the origin of replication.
2. Helicase opens up the DNA-forming replication forks; these are extended in both directions.
3. Single-strand binding proteins coat the DNA around the replication fork to prevent rewinding
of the DNA.
4. Topoisomerase binds at the region ahead of the replication fork to prevent supercoiling (over-
winding).
5. Primase synthesizes RNA primers complementary to the DNA strand.
6. DNA polymerase III starts adding nucleotides to the 3′-OH (sugar) end of the primer.
7. Elongation of both the lagging and the leading strand continues.
8. RNA primers are removed and gaps are filled with DNA by DNA pol I.
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9. The gaps between the DNA fragments are sealed by DNA ligase.
The enzymes involved in prokaryotic DNA replication and the functions of each.
Enzyme/protein Specific Function
DNA pol I Exonuclease activity removes RNA primer and replaces with newly
synthesized DNA
DNA pol II Repair function
DNA pol III Main enzyme that adds nucleotides in the 5′-3′ direction
Helicase Opens the DNA helix by breaking hydrogen bonds between the nitrogenous
bases
Ligase Seals the gaps between the Okazaki fragments to create one continuous DNA
strand
Primase Synthesizes RNA primers needed to start replication
Sliding Clamp Helps to hold the DNA polymerase in place when nucleotides are being added
Topoisomerase Helps relieve the stress on DNA when unwinding by causing breaks and then
resealing the DNA.
Single-strand
binding
proteins (SSB)
Binds to single-stranded DNA to avoid DNA rewinding back.
The main strand can be stretched out by one groundwork alone, though the slacking strand needs
another introduction for every one of the short Okazaki sections. The general bearing of the
slacking strand will be 3′ to 5′, and that of the main strand 5′ to 3′. A protein called the sliding
clamp holds the DNA polymerase set up as it keeps on adding nucleotides. The sliding clamp is a
ring-formed protein that ties to the DNA and holds the polymerase set up. Topoisomerase
forestalls the over-twisting of the DNA double helix in front of the replication fork as the DNA
is opening up; it does as such by causing impermanent scratches in the DNA helix and afterward
resealing it. As amalgamation continues, the RNA groundworks are supplanted by DNA pol I,
what separates the RNA and fills the holes with DNA nucleotides. The scratches that stay
between the recently blended DNA (that supplanted the RNA preliminary) and the recently
combined DNA are fixed by the enzyme DNA ligase that catalyzes the arrangement of
phosphodiester linkage between the 3′-Goodness end of one nucleotide and the 5′ phosphate end
of the other part.
References;
1. Bramhill,D. and Kornberg,A. (1988)
2. Bramhill,D and Kornberg,A. (1988)
3. Schnos,M.,Zahn,K.,Inman,R.B., and Blattner,F. (1988)
4. Mukherjee,S.,Patel,I., and Bastia,D. (1985)
