Post on 04-Oct-2020
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 dies Mouse healthy Mouse healthy
Living S cells
RESULTS
EXPERIMENT
1
Bacterial cell
Phage head
Tail sheath
Tail fiber
DNA
100
nm
2
EXPERIMENT
Phage
DNA
Bacterial cell
Radioactive protein
Radioactive DNA
Batch 1: radioactive sulfur (35S)
Batch 2: radioactive phosphorus (32P)
Empty protein shell
Phage DNA
Centrifuge
Centrifuge
Pellet
Pellet (bacterial cells and contents)
Radioactivity (phage protein) in liquid
Radioactivity (phage DNA) in pellet
3
Sugar–phosphate backbone
5ʹ′ end
Nitrogenous bases
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
DNA nucleotide
Sugar (deoxyribose) 3ʹ′ end
Phosphate
4
(a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA
5
(c) Space-filling model
Hydrogen bond 3ʹ′ end
5ʹ′ end
3.4 nm
0.34 nm
3ʹ′ end
5ʹ′ end
(b) Partial chemical structure (a) Key features of DNA structure
1 nm
6
Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width consistent with X-ray data
7
Cytosine (C)
Adenine (A) Thymine (T)
Guanine (G)
8
A T
G C
T A
T A
G C
(a) Parent molecule
A T
G C
T A
T A
G C
(c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand
(b) Separation of strands
A T
G C
T A
T A
G C
A T
G C
T A
T A
G C
9
Parent cell First replication
Second replication
(a) Conservative model
(b) Semiconserva- tive model
(c) Dispersive model
10
EXPERIMENT
RESULTS
CONCLUSION
1 2
4 3
Conservative model
Semiconservative model
Dispersive model
Bacteria cultured in medium containing 15N
Bacteria transferred to medium containing 14N
DNA sample centrifuged after 20 min (after first application)
DNA sample centrifuged after 40 min (after second replication) More
dense
Less dense
Second replication First replication
11
Origin of replication Parental (template) strand
Daughter (new) strand
Replication fork
Replication bubble
Two daughter DNA molecules
(a) Origins of replication in E. coli
Origin of replication Double-stranded DNA molecule
Parental (template) strand Daughter (new) strand
Bubble Replication fork
Two daughter DNA molecules
(b) Origins of replication in eukaryotes
0.5 µm
0.25 µm
Double- stranded DNA molecule
12
Topoisomerase
Helicase
Primase Single-strand binding proteins
RNA primer
5ʹ′ 5ʹ′
5ʹ′ 3ʹ′
3ʹ′
3ʹ′
13
A
C
T
G
G
G
G C
C C
C
C
A
A
A
T
T
New strand 5ʹ′ end
Template strand 3ʹ′ end 5ʹ′ end 3ʹ′ end
3ʹ′ end
5ʹ′ end 5ʹ′ end
3ʹ′ end
Base
Sugar
Phosphate
Nucleoside triphosphate
Pyrophosphate
DNA polymerase
14
Leading strand
Overview
Origin of replication Lagging strand
Leading strand Lagging strand
Primer
Overall directions of replication
Origin of replication
RNA primer
“Sliding clamp”
DNA poll III Parental DNA
5ʹ′
3ʹ′
3ʹ′
3ʹ′
3ʹ′
5ʹ′
5ʹ′
5ʹ′
5ʹ′
5ʹ′
15
Overview
Origin of replication
Leading strand
Leading strand
Lagging strand
Lagging strand
Overall directions of replication
1 2
16
Template strand
5ʹ′
5ʹ′ 3ʹ′
3ʹ′
RNA primer 3ʹ′ 5ʹ′
5ʹ′
3ʹ′
1
1 3ʹ′
3ʹ′ 5ʹ′
5ʹ′
Okazaki fragment
1 2
3ʹ′
3ʹ′
5ʹ′
5ʹ′
1 2
3ʹ′
3ʹ′
5ʹ′
5ʹ′
1 2
5ʹ′
5ʹ′
3ʹ′
3ʹ′
Overall direction of replication
17
Overview Origin of replication
Leading strand
Leading strand
Lagging strand
Lagging strand Overall directions
of replication
Leading strand
Lagging strand
Helicase
Parental DNA
DNA pol III
Primer Primase
DNA ligase
DNA pol III
DNA pol I
Single-strand binding protein
5ʹ′
3ʹ′
5ʹ′
5ʹ′
5ʹ′
5ʹ′
3ʹ′
3ʹ′
3ʹ′
3ʹ′ 1 3 2
4
18
Nuclease
DNA polymerase
DNA ligase
19
Ends of parental DNA strands
Leading strand
Lagging strand
Lagging strand
Last fragment Previous fragment
Parental strand
RNA primer
Removal of primers and replacement with DNA where a 3ʹ′ end is available
Second round of replication
New leading strand
New lagging strand
Further rounds of replication
Shorter and shorter daughter molecules
5ʹ′
3ʹ′
3ʹ′
3ʹ′
3ʹ′
3ʹ′
5ʹ′
5ʹ′
5ʹ′
5ʹ′
20
DNA double helix (2 nm in diameter)
Nucleosome (10 nm in diameter)
Histones Histone tail H1
DNA, the double helix Histones Nucleosomes, or “beads on a string” (10-nm fiber)
21
30-nm fiber
Chromatid (700 nm)
Loops Scaffold
300-nm fiber
Replicated chromosome (1,400 nm)
30-nm fiber Looped domains (300-nm fiber)
Metaphase chromosome
22