1. Chapter 16: The Molecular Basis of Inheritance (DNA)
Zooming in on DNA

2. Mixture of heat-killed S cells and living R cells Living S cells
(control)
Living R cells
(control)
Heat-killed
S cells (control)
RESULTS
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells
are found in
blood sample

3. LE 16-3
Phage
head
Tail
Tail fiber
DNA
100 nm
Bacterial
cell

4. Activity: Hersey Chase Experiment
LE 16-4
Empty
protein shell
Radioactive
protein
Radioactivity
(phage protein)
in liquid
Phage
Bacterial cell
Batch 1:
Sulfur (35S)
DNA
Phage
DNA
Centrifuge
Radioactive
DNA
Pellet (bacterial
cells and contents)
Batch 2:
Phosphorus (32P)
Centrifuge
Radioactivity
(phage DNA)
in pellet
Pellet
Activity: Hersey Chase Experiment

5. LE 16-5 Sugar–phosphate backbone Nitrogenous bases 5 end Thymine (T)
Adenine (A)
Cytosine (C)
Phosphate
DNA nucleotide
Sugar (deoxyribose)
3 end
Guanine (G)

6. Chargaff
DNAi.org

7. Franklin’s X-ray diffraction photograph of DNA
LE 16-6
Rosalind Franklin
Franklin’s X-ray diffraction
photograph of DNA
DNAi.org

8. Figure 16-01
DNAi.org

9. Purine + purine: too wide
LE 16-UN298
Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width
consistent with X-ray data
DNAi.org

10. Sugar Sugar Adenine (A) Thymine (T) Sugar Sugar Guanine (G)
LE 16-8
Sugar
Sugar
Adenine (A)
Thymine (T)
Sugar
Sugar
Guanine (G)
Cytosine (C)

11. Activity: DNA & RNA Structure Activity: DNA Double Helix
5 end
Hydrogen bond
3 end
1 nm
3.4 nm
3 end
0.34 nm
5 end
Key features of DNA structure
Partial chemical structure
Space-filling model
Activity: DNA & RNA Structure
DNAi.org
Activity: DNA Double Helix

12. LE 16-9_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.
Each parental strand now serves as a template that determines the order of nucleotides along a new, complementary strand.
The nucleotides are connected to form the sugar-phosphate back-
bones of the new strands. Each “daughter” DNA
molecule consists of one parental strand and one new strand.

13. LE 16-10 First Second replication replication Parent cell
Conservative model. The two parental strands reassociate after acting as templates for new strands, thus restoring the parental double helix.
Semiconservative model. The two strands of the parental
molecule
separate, and each functions as a template for synthesis of a new, comple-mentary strand.
Dispersive model. Each strand of both daughter molecules contains
a mixture of
old and newly synthesized
DNA.

14. Meselson & Stahl LE 16-11 Bacteria cultured in medium containing 15N
transferred to
medium
containing
14N
Meselson & Stahl
DNA sample
centrifuged
after 20 min
(after first
replication)
DNA sample
centrifuged
after 40 min
(after second
replication)
Less
dense
More
dense
First replication
Second replication
Conservative
model
Semiconservative
model
Dispersive
model

16. Activity: DNA Replication: An Overview
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).
Activity: DNA Replication: An Overview

17. Activity: DNA Replication: A Closer Look
LE 16-13
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
Activity: DNA Replication: A Closer Look

18. Overall direction of replication
LE 16-14 3¢
Parental DNA 5¢
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

19. LE 16-15_6 Primase joins RNA nucleotides into a primer. 3¢ 5¢ 5¢ 3¢
Template
strand
DNA pol III adds
DNA nucleotides to
the primer, forming
an Okazaki fragment. 3¢
RNA primer 3¢ 5¢ 5¢
After reaching the
next RNA primer (not
shown), DNA pol III
falls off.
Okazaki
fragment 3¢ 3¢ 5¢ 5¢
After the second fragment is
primed, DNA pol III adds DNA
nucleotides until it reaches the
first primer and falls off. 5¢ 3¢ 3¢ 5¢
DNA pol I replaces
the RNA with DNA,
adding to the 3¢ end
of fragment 2. 5¢ 3¢ 3¢ 5¢
DNA ligase forms a
bond between the newest
DNA and the adjacent DNA
of fragment 1.
The lagging
strand in the region
is now complete. 5¢ 3¢ 3¢ 5¢
Overall direction of replication

20. Activity: DNA Replication: A Review
LE 16-16
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¢
DNAi.org
Activity: DNA Replication: A Review

21. Proofreading and Repair
LE 16-17
A thymine dimer
distorts the DNA molecule.
Proofreading and Repair
A nuclease enzyme cuts
the damaged DNA strand
at two points and the
damaged section is
removed.
Nuclease
Repair synthesis by
a DNA polymerase
fills in the missing
nucleotides.
DNA
polymerase
DNA
ligase
DNA ligase seals the
free end of the new DNA
to the old DNA, making the
strand complete.

22. Telomeres LE 16-18 5¢ End of parental DNA strands Leading strand
Lagging strand 3¢
Last fragment
Previous fragment
RNA primer
Telomeres
Lagging strand 5¢ 3¢
Primer removed but
cannot be replaced
with DNA because
no 3¢ end available
for DNA polymerase
Removal of primers and
replacement with DNA
where a 3¢ end is available 5¢ 3¢
Second round
of replication 5¢
New leading strand 3¢
New leading strand 5¢ 3¢
Further rounds
of replication
Shorter and shorter
daughter molecules