1. Determining the Method of DNA Replication
Replication of DNA
Determining the Method of DNA Replication

2. DNA Replication What is replication?
“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”, Watson and Crick

3. Overview of DNA Replication
Helicase unwinds the DNA
Replication bubbles form
Complementary base pairs inserted
DNA polymerase
Joining
DNA ligase

4. Which Type of Replication Occurs?
Conservative
Parental strands get back together
Semiconservative
Parental strands serve as template
Dispersive
Copy short chunks

5. Types of Replication

7. Meselsen and Stahl’s Experiment
They made predictions for each possible type of replication
They conducted experiment and gathered data
Their conclusion was made by comparing results to predictions

8. Predictions of DNA Band Location for Each Type of Replication
Semiconservative
Dispersive
Conservative
L I H
P1 (0 Gen) X
F1 (1 Gen)
X X
F2 (2 Gen)
X X

9. Experimental Results Showing Band Locations
The Experiment

10. Replication of DNA
DNA replication is the process of copying a DNA molecule.
Replication is semiconservative, with each strand of the original double helix (parental molecule) serving as a template (mould or model) for a new strand in a daughter molecule. 10

11. Replication: Eukaryotic
DNA replication begins at numerous points along linear chromosome
DNA unwinds and unzips into two strands
Each old strand of DNA serves as a template for a new strand
Complementary base-pairing forms new strand on each old strand
Requires enzyme DNA polymerase 11

12. Replication: Eukaryotic
Replication bubbles spread bi-directionally until they meet
The complementary nucleotides join to form new strands. Each daughter DNA molecule contains an old strand and a new strand.
Replication is semiconservative:
One original strand is conserved in each daughter molecule i.e. each daughter double helix has one parental strand and one new strand. 12

13. Animation
Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

14. Science Focus: Aspects of DNA Replication
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. OH P
is attached here 5¢
base is attached here
CH2 O OH 4¢ C H H C 1¢ 1 H 3¢ C C H 2¢ OH H
Deoxyribose molecule 2
DNA polymerase
attaches a new
nucleotide to the 3
carbon of the
previous nucleotide.
5¢ end P T P A P P G C
3¢ end P P C G 5¢ P 3¢ P T A P C G P
template strand DN A
polymerase
3¢ end
5¢ end P 4
leading new strand
template strand
Direction of replication
new strand 3¢ 3
helicase at replication fork
RNA primer
template strand 6
Okazaki fragment 3¢ 5
lagging strand 5¢ 5¢
parental DN A
helix 7
DNA ligase
DNA polymerase 3¢
Replication fork introduces complications 14

15. Replication: Prokaryotic
Prokaryotic Replication
Bacteria have a single circular loop
Replication moves around the circular DNA molecule in both directions
Produces two identical circles
Cell divides between circles, as fast as every 20 minutes 15

16. Replication: Prokaryotic vs. Eukaryotic
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
origin
replication is
complete
replication is
occurring in
two directions
a. Replication in prokaryotes
replication fork
replication bubble
parental strand
new DNA
duplexes
daughter strand
b. Replication in eukaryotes 16