DNA replication

1. SUPERVISOR:
PROF-DR/ NOHA MANSOUR

2. Content
Introduction (abstract)
DNA Replication
Types of DNA Replication
Prokaryotic & Eukaryotic Replication
Replication Enzymes & Proteins
Steps of Replication
Inhibitors of DNA Replication
References

3. Introduction
Everyday cell stores its genetic information in the DNA .
 Before a cell divides , this DNA needs to be duplicated , so that the genetic
information can be transferred to the daughter cells .
This process of duplicating of a cell is carried out through a highly coordinated
process called
Replication DNA
This process involves specialized enzymes and proteins .
 These enzymes and proteins act within a multiprotein complex called Replisome .
 despite the difference between prokaryotic and eukaryotic cells , the DNA
Replication is conserved in all kingdoms of life , further underlining its essential
role in nature.

4. DNA Replication
DNA Replication means to produce new
molecules that have the same base
sequence .
 It is a biological process that occurs in
all living organisms and copies their exact
DNA .
 It is the bases for biological inheritance .
It is a reaction in which daughter DNAs
are synthesized using the partner DNAs as
a template .

5. Types

6. Prokaryotic&EukaryoticReplication
Prokaryotic Replication Eukaryotic Replication
 Have circular DNA .
 Replication occurs at one site ,
producing 2 replication forks and
proceeds in opposite direction.
 Have linear DNA .
 Replication occurs at many sites
producing 2 replication forks and
proceeds in opposite direction.

7. ReplicationEnzymes&Proteins
DNA polymerase :match the
correct nucleotides then join .
 Helicase : unwind the DNA and milt
it .
Primase : provides an DNA primer
to start polymerization .

8. StepsofReplication
The first major step for the DNA Replication to take place is the breaking of hydrogen bonds
between bases of the two antiparallel strand.
The un wounding of the two strands is the starting point.
 The splitting happens in places of the chain which are rich in A-T. That is because there are only
two bonds between Adenine and Thymine (there are three hydrogen bonds between Cytosine and
Guanine).
Helicase is the enzyme that splits the two strands. The structure that is created is known as
“Replication Fork”.
In order for DNA replication to begin,
the double stranded DNA helix must first be opened.
The sites where this process first occurs are called replication organs .
 Helicase unwinds the two single strands.



9. The elongation process is different for the 5’-3’ and 3’-5’ template.
a)5’-3’ Template : The 3’-5’ proceeding daughter strand – that uses a
5’-3’ template – is called leading strand because DNA Polymerase(3)
can “read” the template and continuously adds nucleotides .
Once a RNA primer has been laid down by primase , the DNA
polymerase(3) can build the second strand continuously and in the same
direction that the double helix is being opened. To complete the process , DNA
polymerase(1) replaces the RNA primer with DNA .
3’-5’ Template : The 3’-5’ template cannot be “read” by DNA
Polymerase(3) . The replication of this template is complicated and the
new strand is called lagging strand. In the lagging strand the RNA
Primase adds more RNA Primers . DNA polymerase(3) reads the
template and lengthens the bursts. The gap between two RNA primers is
called “Okazaki Fragments”.

10.  The last step of DNA Replication is the Termination. This process happens
when the DNA Polymerase reaches to an end of strands. We can easily
understand that in the last section of the lagging strand, when the RNA primer
removed, it is not possible for the DNA Polymerase to seal the gap (because there
is no primer). So, the end of the parental strand where the last primer binds isn’t
replicated. These ends of linear (chromosomal) DNA consists of noncoding
DNA that contains repeat sequences and are called telomeres. As a result, a part
of the telomeres is removed in every cycle of DNA Replication.
 The DNA Replication is not completed before a mechanism of repair fixes
possible errors caused during the replication. Enzymes like nucleases remove the
wrong nucleotides and the DNA Polymerase fills the gaps.

12. InhibitorsofDNAReplication
Bacterial DNA Gyrase (Type ll Topoisomerase )
Inhibited by Novobiocin &Nalidixic acid .
 Ciprofloxacin interferes with DNA breakage and rejoining process .
Mammalian Topoisomerase
Inhibited by Etoposide & Adriamycin , used as anticancer drugs .
Nucleoside analogues also inhibit replication and are used as anticancer
drugs .

13. References
http://www.yourgenome.org/facts/what-is-dna-replication
http://www.alyvea.com/biologystudyguides/d
nareplication.php
https://study-biology.wikispaces.com/DNA+Replication
http://biologyprojectjhs.weebly.com/dna-replication.html
http://www.sciencedirect.com/science/article/pii/S138357181630
0407
http://morgansbio205.weebly.com/dna-replication.html

14. Faculty of Pharmacy
Department of Biochemistry
RESEARCH ON / DNA REPLICATION
Student
Aml Nashaat Taher (246)
Aml Hesham hussain (247)
Omnia Ebrahem Rashad (248)
Omnia Ibrahem Abdel-rehem (249)
Omnia Ahmed Ibrahem (250)
SUPERVISOR
PROF-DR / NOHA MANSOUR