DNA replication is the process by which DNA makes a copy of itself during cell division. It involves unwinding the DNA double helix structure into single strands, which then serve as templates for new strands to be synthesized. DNA polymerase enzymes carry out the synthesis of new strands. The leading strand is synthesized continuously while the lagging strand is synthesized in fragments that are later joined together. DNA replication results in two identical DNA molecules each with one original and one new strand of nucleotides.

2. Presented by …summaya asghar

3. Dna replication

5.  DNA is an essential molecule for life. It acts
like a recipe holding the instructions telling
our bodies how to develop and function.

6.  DNA is a long thin molecule made up of
something called nucleotides.
 There are four different types of nucleotides
and .
 They are usually represented by their first
letter:
 A- adenine
 T- thymine
 C - cytosine
 G - guanine

8.  DNA replication is
the process by which
DNA makes a copy
of itself during cell
division.

11. DNA polymerases are a
family of enzymes that
carry out all forms of DNA
replication.

12.  The first step in DNA replication is to ‘unzip’
the double helix structure of
the DNA molecule.
 This is carried out by an enzyme called
helicase which breaks the hydrogen
bonds holding the complementary bases of
DNA together (A with T, C with G).

14.  The separation of the two single strands of
DNA creates a ‘Y’ shape called a replication
‘fork’.

15.  The two separated strands will act as
templates for making the new strands of
DNA.
 One of the strands is oriented in the 3’ to 5’
direction (towards the replication fork), this is
the leading strand.

17.  The other strand is oriented in the 5’ to 3’
direction (away from the replication fork), this
is the lagging strand.
 As a result of their different orientations, the
two strands are replicated differently:

19.  Once all of the bases are matched up (A with
T, C with G), an enzyme called exonuclease
strips away the primer(s).
 The gaps where the primer(s) were are then
filled by yet more complementary
nucleotides.

20.  The new strand is proofread to make sure
there are no mistakes in the new DNA
sequence.

22.  The result of DNA replication is two DNA
molecules consisting of one new and one old
chain of nucleotides.

24.  DNA Replication, like all biological
polymerization processes, proceeds in three
enzymatically catalyzed and coordinated
steps:
 initiation
 elongation and
 termination

28.  Imperfect DNA replication results in mutations. Berg JM, Tymoczko JL, Stryer L, Clarke ND
(2002). "Chapter 27: DNA Replication, Recombination, and Repair".Biochemistry. W.H. Freeman
and Company. ISBN 0-7167-3051-0.
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Repair, and Recombination". Molecular Biology of the Cell. Garland Science. ISBN 0-8153-3218-
1.
 Berg JM, Tymoczko JL, Stryer L, Clarke ND (2002). "Chapter 27, Section 4: DNA Replication of
Both Strands Proceeds Rapidly from Specific Start Sites".Biochemistry. W.H. Freeman and
Company. ISBN 0-7167-3051-0.
 Alberts, B., et al., Molecular Biology of the Cell, Garland Science, 4th ed., 2002, pp. 238–
240 ISBN 0-8153-3218-1
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978-1-4051-0379-4
 Berg JM, Tymoczko JL, Stryer L, Clarke ND (2002). Biochemistry. W.H. Freeman and
Company. ISBN 0-7167-3051-0. Chapter 27, Section 2: DNA Polymerases Require a Template
and a Primer
 McCulloch SD, Kunkel TA (January 2008). "The fidelity of DNA synthesis by eukaryotic
replicative and translesion synthesis polymerases". Cell Research 18(1): 148–
61. doi:10.1038/cr.2008.4. PMC 3639319. PMID 18166979.
 McCarthy D, Minner C, Bernstein H, Bernstein C (1976). "DNA elongation rates and growing
point distributions of wild-type phage T4 and a DNA-delay amber mutant". J Mol Biol 106 (4):
963–81. doi:10.1016/0022-2836(76)90346-6.PMID 789903.
 Drake JW (1970) The Molecular Basis of Mutation. Holden-Day, San FranciscoISBN
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