bacterial cell phage head tail sheath tail fiber dna 100 nm 1
TRANSCRIPT
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Bacterial cell
Phage head
Tail sheath
Tail fiber
DNA
100
nm
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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
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Sugar–phosphate backbone
5 end
Nitrogenous
bases
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
DNA nucleotide
Sugar (deoxyribose)
3 end
Phosphate
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(a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA
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(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
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Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine + pyrimidine: width consistent with X-ray data
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Cytosine (C)
Adenine (A) Thymine (T)
Guanine (G)
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A T
GC
T A
TA
G C
(a) Parent molecule
A T
GC
T A
TA
G 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
TA
G C
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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) 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
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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
Base
Sugar
Phosphate
Nucleoside triphosphate
Pyrophosphate
DNA polymerase
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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)
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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
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