Tail sheath Tail fiber DNA 100 nm 1 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1 radioactive sulfur 35 S Batch 2 radioactive phosphorus 32 P ID: 778868
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Slide1
Bacterial
cell
Phage head
Tail sheath
Tail fiber
DNA
100 nm
1
Slide2EXPERIMENT
Phage
DNA
Bacterial cell
Radioactive protein
Radioactive DNA
Batch 1: radioactive sulfur (
35
S)
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
2
Slide3Sugar–phosphate
backbone
5 end
Nitrogenous bases
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
DNA nucleotide
Sugar (deoxyribose) 3 end
Phosphate
3
Slide4(a) Rosalind Franklin
(b) Franklin’s X-ray diffraction
photograph of DNA
4
Slide5(c) Space-filling model
Hydrogen bond
3
end
5 end
3.4 nm
0.34 nm
3 end
5 end
(b) Partial chemical structure
(a) Key features of DNA structure
1 nm
5
Slide6Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width consistent with X-ray data
6
Slide7Cytosine (C)
Adenine (A)
Thymine (T)
Guanine (G)
7
Slide8A
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
8
Slide9Origin 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
9
Slide10A
C
T
G
G
G
G
C
C
C
C
C
A
A
A
T
T
T
New strand 5
end
Template strand 3
end
5
end
3
end
3
end
5
end
5
end
3
end
Base
Sugar
Phosphate
Nucleoside triphosphate
Pyrophosphate
DNA polymerase
10
Slide11DNA 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)
11
Slide1230-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
12