DNA replication is the process where a cell makes an exact copy of its DNA. It occurs in three main steps: unwinding of the DNA double helix by helicase, addition of nucleotides to both strands by DNA polymerase, and ligation of the nucleotide fragments by DNA ligase. The two resulting DNA molecules each have one original parent strand and one new daughter strand. DNA replication ensures fidelity of the genetic material and is essential for cell division and reproduction.

1. DNA
Replication

2. What does DNA look
like?
 DNA
has..
A
sugar/phosphate
backbone
 4 Chemical bases
Sugar

3. The bases
 It
is composed of 4
chemical bases:
Adenine (A), Thymine
(T), Cytosine (C) and
Guanine (G).
A
always pairs with T

4. The Bases
C
always pairs with G
 The
pairs are held together by hydrogen
bonds.

5. What does DNA do?

DNA: deoxy ribose nucleic acid
 DNA
is the genetic code.

It determines our physical characteristics: from our
hair color to what we are allergic to.

Our DNA codes for 20 amino acids which are the
building blocks of life.

6. What Is DNA Replication
 DNA
Replication is the
process in which the
DNA within a cell
makes an exact copy
of itself.

7. DNA Replication - the very basics
The basics of DNA REPLICATION
 Unwind – Unzip – Add nucleotides – wind it all back up.


If only it could be that simple
Two things make it a little more complicated
 DNA is a VERY LONG double helix chemical molecule
 It has a anti-parallel structure

8. It’s a long Double
Helix
Anti-parallel
structure of
DNA

9. -

10. DNA Replication
Replication occurs during Interphase
Replication
fork
Replication
fork
Replication
bubble
Hydrogen
bond
DNA replication is the process where an entire double-stranded DNA is
copied to produce a second, identical DNA double helix.

11. DNA Replication
DNA
helicase
• Helicase unwinds the double helix starting at a replication bubble.
• The two strands separate as the hydrogen bonds between base pairs are
broken.
• Two replication forks form and the DNA is unwound in opposite directions.

12. DNA Replication
•Helicase has completed unwinding the DNA strand.
•Single stranded Binding Proteins keep the two strands from reannealing (coming back together).

13. DNA Replication
Leading Strand
Primase
RNA Primer
Lagging Strand
•Primase is an RNA polymerase that makes the RNA primer.
•These primers “tell” the DNA polymerase where to start copying the
DNA.

14. DNA Replication
Leading Strand
5’
3’
Direction of Replication
DNA Polymerase
5’
Direction of Replication
Lagging Strand
3’
• The DNA polymerase starts at the 3’ end of the RNA primer of the leading stand
CONTINUOUSLY.
• DNA is copied in 5’ to 3’ direction.
• DNA polymerase copies the lagging strand DIS- continuously.

15. DNA Replication
• The dis-continuous pieces of DNA copied on the lagging
strand are known as Okazaki fragments.

16. DNA Replication
Another DNA Polymerase removes the RNA primers and
replaces them with DNA.

17. DNA Replication
ligase
Finally the gaps in the sugar phosphate backbone are
sealed by DNA ligase
There are now 2 identical double helices of DNA.

18. REACTION:
o
The DNA occurs simultaneously forming
sister chromatids.
o
Nucleotides should always be in pairs.
o
Nucleotides are held together with loose
hydrogen bonds.

19. o
Every cell in our body has the same copy
of DNA, and the DNA will copy itself trillion
of times in our lifetime.
o
Every copy of the DNA contains half of its
original strand.
o
DNA replication is semiconservative with
each existing strand serving as template
for synthesis of new strand.

20. o
Replication begins at specific location called
REPLICATION.
o
On one strand (leading strand) synthesis is
continuous
o
On the other strand (lagging strand) synthesis is
discontinuous.

21. The 2 strands is producing a series
Of okazaki fragments that must be
Ligased together
o

22. DNA Replication ANIMATION
 http://www.wiley.com/college/pratt/0471
393878/student/animations/dna_replicati
on/index.html
 http://www.youtube.com/watch?v=teV6
2zrm2P0

23. Done by:
Lume Landman
201218257

24. References

Mohapatra , L
http://www.slideshare.net/lopamohapatra39/dnareplication-29922117?qid=f160c09e-4986-412e-b81eccf2da2dcab5&v=default&b=&from_search=1 (Accessed
on 7 March)

Serwelas, CM and Esquivel, CL
http://www.slideshare.net/claudeaa/dna-replication11970385 (Accessed on 7 March)

http://www.slideshare.net/ihmcbiology1213/dnareplication-15152639(Accessed on 7 March)