DNA replication is initiated by enzymes that unwind and separate the double helix, including DNA gyrase and helicase. Primase then lays down RNA primers to which DNA polymerase can add complementary DNA nucleotides to the 3' ends of the primers, elongating the strands. One strand is synthesized continuously as the leading strand while the other is synthesized in fragments called Okazaki fragments that are later joined by ligase. Several DNA polymerases and exonucleases work together to accurately copy the genetic material.

1. DNA STRUCTURE AND
RUPLICATION
PRESENTATION OF ZOOLOGY

2. DNA THE GENATIC METRIAL:
 Study of DNA how store information knowns as “MOLECULAR BIOLOGY”
 DNA is a double stranded molecule
 which have components:
 Nitrogenous bases
 Deoxyribose sugar
 Phosphates
Phosphat
e group
Nitrogenous
bases
Ribose sugers

3. • Like ladder, with the
rails of the ladder
consisting of
alternating sugar-
phosphate groups
5’3’
3, 5’
• Stands are anti parallel
The entire molecule is twisted into a
Right hand helix, with one complete
Spinal every 10 base pair.

4. (a)Nucleotides of one strand of
nucleic acid join by linking the
phosphate of one of one nucleotides
to the 3’ Carbon of an adjacent
nucleotides. Dashed line between
the nitrogenous bases indicates
“HYDROGEN BONDING”.3 dashes
are between cytosine and guanine,
and 2 between thymine & adenine .
(b) Three-dimentional
representation of DNA. The anti
parallel nature of the strands is
indicated by the curved arrows.

5.  Nitrogenous bases are specify to attached with each other that is:
 Cytosine always attached with Guanine
&
 Adenine always attached with Thymine.

Adenine
Cytosine
ThymineGuanine
The sequence of the nitrogenous bases
are responsible for the different trades
represent by organisms.

6. Replication of dna
Replication began simultaneously at many initiation sites along the length of
chromosomes in eukaryotic cells and in prokaryotes only one inisiation site is available.
there are following Enzymes are evolved of replication of DNA:
1. DNA gyrase & Helicase
2. Primase
3. DNA polymerase I, II, III
4. Exonuclease
5. DNA ligase.

7. Frist step of replication initiation phase
First the enzyme DNA gyrase open the turns of DNA and turn into straight ladder. At the same times
unzipping occurs.
An enzyme called Helicase unzip the DNA strand and replication bubble and fork is formed at a
particular site. The two strands gradually separated from each other and give rise a bubble like
appearance
Helicase

8. After the breakdown of base pairs, single strands of DNA prevented to pair up again by specific proteins
called Single stranded binding (SSB).
Each side of replication bubble is now termed as replication Fork.
A primase enzyme is attached for initiation of the replication which is carried out by DNA polymerase.
DNA polymerase can not be functioned unless some nucleotides are arranged on template.so RNA
primer is necessary.
RNA primase

9. After the establishment of primer the DNA polymerase is active.
DNA polymerase is of three types:
 DNA polymerase I ( exonuclease )
 DNA polymerase II (involve in repairing of DNA throughout the life)
 DNA polymerase III (main function in replication)

10.  The DNA polymerase add nitrogenous basses on only 3’ end so replication began from 5’to 3’
 The new formed strand is continuous and called leading strand. One subunit of DNA polymerase also
posses ability to remove wrong nucleotides, if it is added mistakenly . This ability is called
PROOFREADING

11.  The second strand is lagging strand which is formed not continuously.
 On this strand Okazaki fragments are formed by DNA polymerase

12. Okazaki fragments are small part of nucleotides which made by DNA polymerase.
After every Okazaki fragment new primer is formed. And DNA polymerase jumped next for making new
Okazaki fragment. This strands replicate away from fork and called lagging strand
Here formed
new Okazaki

13.  Then the RNA nucleotides are removed by an enzyme called Exoneuclase and add DNA nucleotides
here.
 Okazaki fragments are discontinues so an enzyme called DNA ligase seals the gaps and two daughter
strands are formed.

14. Old strand
New strand

16. summary
 Enzymes used:
 DNA gyrase
 Protein SSB (single stranded binding)
 Helicase
 Primase
 DNA polymerase I, II, III
 Exonuclease (polymerase I)