This about the DNA and mechanism of DNA replication. DNA IS A BLUE PRINT OF LIFE.DNA is a major store of genetic information.Located in nucleus and mitochondria.

1. MECHANISM OF DNA
REPLICATION
By
Gayathri. V
B.Sc.(Microbiology)
ANJA College,
Sivakasi .

2. DNA
• DNA IS A BLUE PRINT OF LIFE

3. DNA
(DEOXYRIBO NUCLEIC ACID)
• DNA is a major store of genetic information.
• DNA or deoxyribonucleic acid is a genetic material that transfer the genetic
information from one organism to their off spring.
• Located in nucleus and mitochondria.
• The information in DNA is stored as code (made up of A – Adenine, G – Guanine, C
– Cytosine, T – Thymine)
• 99% of base are same. The order of bases determines the individuality.

4. CENTRAL DOGMA
• The flow of information is the cell starts at DNA, which replicates to form more DNA.
• Information is then “transcribed” into RNA.
• And then it is “translated” into protein.
• The proteins do most of the work in the cell.

5. DNA REPLICATION
• The duplication or synthesis of DNA is called replication.

6. DNA REPLICATION IS SEMI CONSERVATIVE
• Each replicated duplex daughter DNA molecule contains one parent
strand and one newly synthesized strand.
• The base pairing rule is always maintained.

7. BASIC REQUREMENT FOR REPLICATION
SUBSTRATES:
• The four deoxyribonucleoside triphosphate.
• {dATP,dGTP,dCTP ,dTTP}
• Both strands of DNA double helix serve as template for the
synthesis of new daughter DNA strands.
• DNA B protein (Helicase) Unwinds DNA. It acts like zipper
to unzip the DNA
• Primase Synthesizes RNA primer
TEMPLATE:
ENZYMES AND PROTEINS

8. • DNA Topoisomerase I & II Relieves torsional strain by cutting &
joining single strand or both strands.
• DNA ligase Joins Okazaki Fragments.
• DNA A Protein Opens duplex at origin of replication.
• SSB (Single Strand Binding Protein) Binds separated single
stranded DNA and stabilizes it.
• Ter binding protein Prevents the helicase from further unwinding
and facilitates termination.
• DNA Polymerase DNA Chain elongation.

9. STEPS OF DNA REPLICATION

10. INITIATION
• During replication of DNA the two complementary strand of DNA uncoil and
separate from one end in a zipper like fashion.
• The enzyme helicase unwinds the two strand and as a result replication fork is
formed.
• As the DNA unwinds, the part of the DNA that is found above the replication fork
becomes supercoils. These are called positive supercoils.
• An enzyme called topoisomerase releases these supercoils.
• Based on separated DNA strands, new strands grow by the addition of nucleotides.

11. • DNA polymerase I, II and III are involved in this
elongation.However these enzymes are not capable of
initiating DNA synthesis.

12. ELONGATION
• For the synthesis of new DNA, two things are required. One is RNA
Primer and the enzyme primase.
• The DNA polymerase moves along the newly formed RNA primer
nucleotides, which leads to the elongation of DNA.
• In the other stand, DNA is synthesized in small fragments called
Okazaki fragments.
• Okazaki fragments are short, newly synthesized DNA Fragments
That Are Formed on the lagging template strand during DNA
replication.

13. • Okazaki fragments are between 1000 and 2000 nucleotides long in
prokaryotes and are approximately 150 nucleotides long in
eukaryotes.
• Two Okazaki fragments are connected into one continuous newly
synthesized complementary strand by enzyme ligase.

14. TERMINATION
• Termination sequences, e.g. “ter”, direct termination of replication.
• A specific protein, ter binding protein, binds these sequences and prevents the
helicase from further unwinding of DNA and facilitates the termination of
replication.
• In the resulting DNA one of the strand is parental and the other is the newer strand
which is formed discontinuously. Hence, it is called semi discontinuous replication.

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