DNA is the genetic material that is faithfully replicated and passed from parents to offspring. James Watson and Francis Crick discovered the double helix structure of DNA in 1953, which explained how DNA could store and replicate the instructions for making organisms. Their model showed that DNA consists of two strands coiled around each other, with nucleotides on the strands bonded together through base pairing with adenine bonding only to thymine and guanine only to cytosine. This allows each strand to serve as a template for duplicating the other, explaining DNA's role in inheritance and allowing organisms to pass genetic information between generations.
Chapter 16: Molecular Basis of InheritanceAngel Vega
KEY CONCEPTS
16.1 DNA is the genetic material
16.2 Many proteins work together in
DNA replication and repair
16.3 A chromosome consists of a DNA molecule packed together with proteins
8. Living S cells
(control)
Living R cells
(control)
Heat-killed
S cells
(control)
Mixture of
heat-killed
S cells and
living R cells
Mouse dies Mouse diesMouse healthy Mouse healthy
Living S cells
EXPERIMENT
RESULTS
Figure 16.2
24. Figure 16.7
3.4 nm
1 nm
0.34 nm
Hydrogen bond
(a) Key features of
DNA structure
Space-filling
model
(c)(b) Partial chemical structure
3′ end
5′ end
3′ end
5′ end
T
T
A
A
G
G
C
C
C
C
C
C
C
C
C
C
C
G
G
G
G
G
G
G
G
G
T
T
T
T
T
T
A
A
A
A
A
A
25. 3.4 nm
1 nm
0.34 nm
Hydrogen bond
(a) Key features of
DNA structure
(b) Partial chemical structure
3′ end
5′ end
3′ end
5′ end
T
T
A
A
G
G
C
C
C
C
C
C
C
C
C
C
C
G
G
G
G
G
G
G
G
G
T
T
T
T
T
T
A
A
A
A
A
A
Figure 16.7a
35. Figure 16.9-2
(a) Parent molecule (b) Separation of
strands
A
A
A
A
A
A
T
T
T
T
T
T
C
C
C
C
G
G
G
G
36. Figure 16.9-3
(a) Parent molecule (b) Separation of
strands
(c)“Daughter” DNA molecules,
each consisting of one
parental strand and one
new strand
A
A
A
A
A
A
A
A
A
A
A
A
T
T
T
T
T
T
T
T
T
T
T
T
C
C
C
C
C
C
C
C
G
G
G
G
G
G
G
G
41. Figure 16.11
Bacteria
cultured in
medium with
15
N (heavy
isotope)
Bacteria
transferred to
medium with
14
N (lighter
isotope)
DNA sample
centrifuged
after first
replication
DNA sample
centrifuged
after second
replication
Less
dense
More
dense
Predictions: First replication Second replication
Conservative
model
Semiconservative
model
Dispersive
model
21
3 4
EXPERIMENT
RESULTS
CONCLUSION
42. Figure 16.11a
Bacteria
cultured in
medium with
15
N (heavy
isotope)
Bacteria
transferred to
medium with
14
N (lighter
isotope)
DNA sample
centrifuged
after first
replication
DNA sample
centrifuged
after second
replication
Less
dense
More
dense
21
3 4
EXPERIMENT
RESULTS
43. Figure 16.11b
Predictions: First replication Second replication
Conservative
model
Semiconservative
model
Dispersive
model
CONCLUSION
46. Figure 16.12
(a) Origin of replication in an E. coli cell (b) Origins of replication in a eukaryotic cell
Origin of
replication
Parental (template) strand
Double-
stranded
DNA molecule
Daughter (new)
strand
Replication
fork
Replication
bubble
Two daughter
DNA molecules
Origin of replication
Double-stranded
DNA molecule
Parental (template)
strand
Daughter (new)
strand
Bubble Replication fork
Two daughter DNA molecules
0.5µm
0.25µm
47. Figure 16.12a
(a) Origin of replication in an E. coli cell
Origin of
replication Parental (template) strand
Double-
stranded
DNA molecule
Daughter (new) strand
Replication fork
Replication
bubble
Two
daughter
DNA molecules
0.5 µm
48. Figure 16.12b
(b) Origins of replication in a eukaryotic cell
Origin of replication
Double-stranded
DNA molecule
Parental (template)
strand
Daughter (new)
strand
Bubble Replication fork
Two daughter DNA molecules
0.25 µm
57. Figure 16.14
New strand Template strand
Sugar
Phosphate Base
Nucleoside
triphosphate
DNA
polymerase
Pyrophosphate
5′
5′
5′
5′
3′
3′
3′
3′
OH
OH
OH
P P i
2 P i
P
P
P
A
A
A
A
T T
T
T
C
C
C
C
C
C
G
G
G
G
60. Figure 16.15
Leading
strand
Lagging
strand
Overview
Origin of replication Lagging
strand
Leading
strand
Primer
Overall directions
of replication
Origin of
replication
RNA primer
Sliding clamp
DNA pol III
Parental DNA
3′
5′
5′
3′
3′
5′
3′
5′
3′
5′
3′
5′
70. Figure 16.16b-5
Template
strand
RNA primer
for fragment 1
Okazaki
fragment 1
RNA primer
for fragment 2
Okazaki
fragment 2
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
5′
5′
5′
5′
5′
5′
5′
5′
5′
5′5′
2
2
1
1
1
1
71. Figure 16.16b-6
Template
strand
RNA primer
for fragment 1
Okazaki
fragment 1
RNA primer
for fragment 2
Okazaki
fragment 2
Overall direction of replication
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
5′
5′
5′
5′
5′
5′
5′
5′
5′
5′5′
5′
2
2
2
1
1
1
1
1
72. Figure 16.17
Overview
Leading
strand
Origin of
replication Lagging
strand
Leading
strandLagging
strand Overall directions
of replicationLeading strand
DNA pol III
DNA pol III Lagging strand
DNA pol I DNA ligase
Primer
Primase
Parental
DNA
5′
5′
5′
5′
5′
3′
3′
3′
3′
3′3 2 1
4
76. Figure 16.18
Parental DNA
DNA pol III
Leading strand
Connecting
protein
Helicase
Lagging strandDNA
pol III
Lagging
strand
template
5′
5′
5′
5′
5′
5′
3′ 3′
3′
3′
3′
3′
81. Figure 16.20
Ends of parental
DNA strands
Leading strand
Lagging strand
Last fragment Next-to-last fragment
Lagging strand RNA primer
Parental strand
Removal of primers and
replacement with DNA
where a 3′ end is available
Second round
of replication
Further rounds
of replication
New leading strand
New lagging strand
Shorter and shorter daughter molecules
3′
3′
3′
3′
3′
5′
5′
5′
5′
5′
82. Figure 16.20a
Ends of parental
DNA strands
Leading strand
Lagging strand
Last fragment Next-to-last fragment
Lagging strand RNA primer
Parental strand
Removal of primers and
replacement with DNA
where a 3′ end is available
3′
3′
3′
5′
5′
5′
83. Figure 16.20b
Second round
of replication
Further rounds
of replication
New leading strand
New lagging strand
Shorter and shorter daughter molecules
3′
3′
3′
5′
5′
5′
90. Figure 16.22a
DNA double helix
(2 nm in diameter)
DNA, the double helix
Nucleosome
(10 nm in diameter)
Histones
Histones
Histone
tail
H1
Nucleosomes, or “beads on
a string” (10-nm fiber)
105. Figure 16.UN03
DNA pol III synthesizes
leading strand continuously
Parental
DNA DNA pol III starts DNA
synthesis at 3′ end of primer,
continues in 5′ → 3′ direction
Origin of
replication
Helicase
Primase synthesizes
a short RNA primer
DNA pol I replaces the RNA
primer with DNA nucleotides
3′
3′
3′
5′
5′
5′
5′
Lagging strand synthesized
in short Okazaki fragments,
later joined by DNA ligase