bacterial cell
Post on 24-Feb-2016
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Bacterial cell
Phage head
Tail sheath
Tail fiber
DNA
100
nm
1
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
2
Sugar–phosphate backbone
5 end
Nitrogenous
bases
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
DNA nucleotide
Sugar (deoxyribose)
3 end
Phosphate
3
(a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA
4
(c) Space-filling model
Hydrogen bond 3 end
5 end
3.4 nm
0.34 nm3 end
5 end
(b) Partial chemical structure(a) Key features of DNA structure
1 nm
5
Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width consistent with X-ray data
6
Cytosine (C)
Adenine (A) Thymine (T)
Guanine (G)7
A T
GC
T A
TA
G C
(a) Parent molecule
A T
GC
T A
TAG C
(c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand
(b) Separation of strands
A T
GC
T A
TA
G C
A T
GC
T A
TAG C
8
Origin of replication Parental (template) strand
Daughter (new) strand
Replication forkReplication bubble
Two daughter DNA molecules
(a) Origins of replication in E. coli
Origin of replication Double-stranded DNA molecule
Parental (template) strandDaughter (new) strand
Bubble Replication fork
Two daughter DNA molecules
(b) Origins of replication in eukaryotes
0.5 µm
0.25 µm
Double-strandedDNA molecule
9
A
C
T
G
G
G
GC
C C
C
C
A
A
AT
T
T
New strand 5 end
Template strand 3 end 5 end 3 end
3 end
5 end5 end
3 end
BaseSugar
Phosphate
Nucleoside triphosphate
Pyrophosphate
DNA polymerase
10
DNA double helix (2 nm in diameter)
Nucleosome(10 nm in diameter)
Histones Histone tailH1
DNA, the double helix Histones Nucleosomes, or “beads on a string” (10-nm fiber)
11
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
12
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