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Fig. 16-17
OverviewOrigin of replication
Leading strand
Leading strand
Lagging strand
Lagging strandOverall 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
5
3
5
5
5
5
3
3
3
313 2
4
Figure 16.18
Parental DNA
DNA pol III
Leading strand
Connectingprotein
Helicase
Lagging strandDNA pol III
Laggingstrandtemplate
5
5
5
5
5
5
3 3
33
3
3
Cool animation of DNA replication (and other stuff)
http://www.ted.com/talks/drew_berry_animations_of_unseeable_biology.html
How do we know all this?
-That the lagging strand is made in fragments
-That DNA ligase joins these fragments together
Mixture ofDNA mol-ecules ofdifferentsizes
Powersource
Powersource
Longermolecules
Cathode Anode
Wells
Gel
Shortermolecules
TECHNIQUE
2
1Gel electrophoresis
DNA Pol III
Where do mutations come from?
E.Coli genome: 4.6 x 10^6 b.p.
H. Sapiens genome (diploid): 6 x 10^9 b.p.
~1 “error” for every 1010 bases replicated
DNA pol III adds the wrong base every 105 bases
How often do mutations occur?
Extra fidelity comes from:1. “Proofreading” by DNA pol III (and pol I)
2. Mismatch repair pathway
E.Coli genome: 4.6 x 10^6 b.p.
H. Sapiens genome (diploid): 6 x 10^9 b.p.
~1 “error” for every 1010 bases replicated
DNA pol III adds the wrong base every 105 bases
How often do mutations occur?
E.Coli genome: 4.6 x 10^6 b.p.
H. Sapiens genome (diploid): 6 x 10^9 b.p.
~1 “error” for every 1010 bases replicated
DNA pol III adds the wrong base every 105 bases
How often do mutations occur?
Extra fidelity comes from:1. “Proofreading” by DNA pol III (and pol I)
2. Mismatch repair pathway
Chemically damaged DNA can lead to much higher rates of mutation
Fig. 16-18
Nuclease
DNA polymerase
DNA ligase
Example of damaged DNA: thymine dimer caused by UV radiation
Nucleotide Excision Repair pathway has removed and replaced damaged bases
Fig. 16-18
Nuclease
DNA polymerase
DNA ligase
Nucleotide Excision Repair pathway removes and replaces damaged bases
Example of damaged DNA: thymine dimer caused by UV radiation
Fig. 16-12b
0.25 µm
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
Eukaryotic replication
Fig. 16-19
Ends of parental DNA strands
Leading strandLagging strand
Lagging strand
Last fragment Previous fragment
Parental strand
RNA primer
Removal of primers and replacement with DNA where a 3 end is available
Second round of replication
New leading strand
New lagging strand
Further rounds of replication
Shorter and shorter daughter molecules
5
3
3
3
3
3
5
5
5
5
Fig. 16-19
Ends of parental DNA strands
Leading strandLagging strand
Lagging strand
Last fragment Previous fragment
Parental strand
RNA primer
Removal of primers and replacement with DNA where a 3 end is available
Second round of replication
New leading strand
New lagging strand
Further rounds of replication
Shorter and shorter daughter molecules
5
3
3
3
3
3
5
5
5
5
Fig. 16-20
1 µm
Staining of telomeres Florescence In Situ Hybridization (FISH)
“probe” = (5’-CTAACC-3’)100
08_Figure37.jpg
Fig. 16-7a
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
Fig. 16-21a
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)
Fig. 16-21b
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
