1. DO NOW: Is it a hydrolysis or dehydration synthesis
DO NOW: Is it a hydrolysis or dehydration synthesis? Support your answer with a minimum of two reasons.

2. Synthesis of an “exact” copy of the entire genome of the cell
DNA Replication
Synthesis of an “exact” copy of the entire genome of the cell

3. The parent molecule has two complementary
strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C.

4. The parent molecule has two complementary
strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C.
The first step in replication is separation of the two DNA strands.

5. LE 16-9_3 The parent molecule has two complementary
strands of DNA. Each base is paired by hydrogen bonding with its specific partner, A with T and G with C.
The first step in replication is separation of the two DNA strands.
Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand.

6. Getting Started: Origins of Replication
Replication begins at special sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble”
A eukaryotic chromosome may have hundreds or even thousands of origins of replication
Replication proceeds in both directions from each origin, until the entire molecule is copied
At the end of each replication bubble is a replication fork, a Y-shaped region where new DNA strands are elongating

7. LE 16-12
Parental (template) strand
0.25 µm
Origin of replication
Daughter (new) strand
Bubble
Replication fork
Two daughter DNA molecules
In eukaryotes, DNA replication begins at may sites
along the giant DNA molecule of each chromosome.
In this micrograph, three replication
bubbles are visible along the DNA
of a cultured Chinese hamster cell
(TEM).

8. DNA polymerase Pyrophosphate Nucleoside triphosphate
New strand
Template strand
5¢ end
3¢ end
5¢ end
3¢ end
Sugar
Base
Phosphate
DNA polymerase
3¢ end
3¢ end
Pyrophosphate
Nucleoside
triphosphate
5¢ end
5¢ end

9. Antiparallel Elongation
The antiparallel structure of the double helix (two strands oriented in opposite directions) affects replication
DNA polymerases add nucleotides only to the free 3end of a growing strand; therefore, a new DNA strand can elongate only in the 5 to 3direction

11. The Basic Principle: Base Pairing to a Template Strand
Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication
In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules
Animation: DNA Replication Overview

12. Along one template strand of DNA, called the leading strand, DNA polymerase can synthesize a complementary strand continuously, moving toward the replication fork
To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork
The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase

13. LE 16-14 3¢ 5¢ Parental DNA Leading strand 5¢ 3¢ Okazaki fragments
Lagging strand 3¢ 5¢
DNA pol III
Template
strand
Leading strand
Lagging strand
Template
strand
DNA ligase
Overall direction of replication

14. LE 16-16 Leading strand Lagging strand Origin of replication Lagging
Overall direction of replication
Leading
strand
Lagging
strand
Origin of replication
Lagging
strand
Leading
strand
OVERVIEW
DNA pol III
Leading
strand
DNA ligase
Replication fork 5¢
DNA pol I 3¢
Primase
Parental DNA
DNA pol III
Lagging
strand
Primer 3¢ 5¢