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

53

5

5

5

5

3

3

3

313 2

4

Figure 16.18

Parental DNA

DNA pol IIILeading 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