MADHESH AGRICULTURAL
UNIVERSITY
Rajbiraj,Sapatari
TOPIC: DNA REPLICATION
Submitted to: Dr.MD Ekram Hussain
Presented By:
Roshani Khatun
INTRODUCTION
DNA replication is the process by which a cell makes an exact copy of its DNA before cell division
Nature of Replication:
Semi-conservative:
Each new DNA molecule has: One parental (old) strand
One newly synthesized strand
Location
Occurs in the nucleus (in eukaryotes)
In prokaryotes, it occurs in the cytoplasm
Timing
Takes place during the S-phase (synthesis phase) of the cell cycle
Basic Requirements
Template DNA strand
Free nucleotides (A, T, G, C) Enzymes
Energy (ATP)
Important Enzymes
Helicase: Unwinds the DNA double helix Topoisomerase: Relieves strain ahead of replication fork Primase: Synthesizes RNA primers
DNA Polymerase: Adds nucleotides in 5' → 3' direction DNA Ligase: Joins Okazaki fragments
Steps of DNA Replication
Replication begins at origin of replication (Ori)
Helicase breaks hydrogen bonds → forms replication fork
DNA polymerase adds nucleotides complementary to template
Two strands formed:
Leading strand
Synthesized continuously (5' → 3') Lagging strand
Synthesized discontinuously as Okazaki fragments
Replication ends when forks meet
RNA primers removed and replaced with DNA Fragments joined by ligase
Direction of Replication
Always occurs in 5' → 3' direction
Base Pairing Rule
Adenine (A) pairs with Thymine (T) Guanine (G) pairs with Cytosine (C)
Proofreading
DNA polymerase checks and corrects errors → ensures high accuracy
Significance:
Ensures genetic continuity
Essential for growth, repair, and reproduction Maintenance of Genetic Stability
Evolution and Diversity Tissue Repair and Regeneration
Cell Division and Growth
THANK YOU