What needs to happen to somatic cells during division

1
Cell Division in Somatic Cells
What needs to happen to somatic cells during
division?

• Make enough of the various cellular components
  for two cells
• Divide the components equally between the two new
  
• (daughter) cells
• Involves karyokinesis (mitosis) and cytokinesis

2
The Cell Cycle and DNA Replication
DNA Synthesis
Gap/Growth Phase 2
Gap/Growth Phase 1
3
Timing of Cell Cycle
Whats going on during this phase that occupies a
significant portion of cell cycle?
4
DNA Replication
Making enough DNA for two cells
5
Models for DNA Replication
6
Models for DNA Replication
7
Models for DNA Replication
8
Models for DNA Replication
9
The Meselson-Stahl Experiment

• Grew E.coli in 15NH4Cl
• This heavy isotope affects the
  centrifugation behavior of DNA in CsCl
• The labeled E.coli were shifted to a 14N
  environment for successive generations

10
Nitrogen in DNA
15N is heavier than 14N and so will make the DNA
heavier
11
The Meselson-Stahl Experiment

• Grew E.coli in 15NH4Cl
• This heavy isotope affects the
  centrifugation behavior of DNA in CsCl
• The labeled E.coli were shifted to a 14N
  environment for successive generations

12
The Meselson-Stahl Experiment
Predictions
Conservative
Semi-Conservative
13
The Meselson-Stahl Experiment
In the dispersive model, all of the generations
would exhibit an intermediate density which would
gradually approach the 14N density.
If F1 rules out conservative model, why do F2 and
F3 rule out the dipersive model?
14
The Meselson-Stahl Experiment
original data
15
Questions for Chapter 11 2, 4, 7, 10, 13 17
16
DNA Replication
What needs to happen in order for DNA to be
replicated?
- Recall what we talked about last class.
How does DNA replicate?
- Semi-conservative replication.
What is the end product of semi-conservative
replication?

• Two double stranded DNA molecules, each comprised
  of
• one old and one new strand.

17
DNA Replication
parental double strand
old strand
old strand
new strand
new strand
daughter double strand
daughter double strand
Making enough DNA for two cells
18
DNA Synthesis Uses 5 to 3 Polymerization
dGTP
DNA Polymerase
dGTP
19
Origin of Replication
The origin of replication is a sequence of
nitrogenous bases on a DNA molecule that signals
the beginning point of replication of the DNA
molecule necessary for DNA replication.
Prokaryotic
Eukaryotic
20
Replication Begins at Distinct ORI Sites

• OriC - in E.coli
• 245 nucleotides long
• Three tandem repeats (13-mer) required for
  the formation of the replication bubble (A-T
  rich)

21
Getting Started
22
Replication Bubble
Other accessory proteins are needed to keep the
bubble open.
23
Priming the Single Stranded DNA for Polymerase
primase
24
DNA Polymerase III in Action
Is replication the same on both leading and
lagging strands?
25
Replication Is Not the Same in Leading and
Lagging Strand
What differs?
26
Eukaryotic Replication Bubble
Remember, there are multiple origins of
replication.
27
Special Cases for DNA Replication Mechanisms

• Telomeres
• Homologous Recombination
• -Crossing Over

28
Human Telomere Structure
29
Telomere Sequences
Vertebrates Human, mouse, Xenopus TTAGGG Filament
ous fungi Neurospora TAGGG Slime
molds Physarum, Didymium TTAGGG
Dictyostelium AG(1-8) Kinetoplastid
Trypanosoma, Crithidia TTAGGG protozoa Ciliated
protozoa Tetrahymena, Glaucoma TTGGGG
Paramecium TTGGG(T/G) Oxytricha,
Stylonychia, TTTTGGGG Euplotes Sporozoite
protozoa Plasmodium TTAGGG(T/C) Higher
plants Arabidopsis TTTAGGG

30
Telomerase A Reverse Transcriptase
31
Telomerase Demo.
created by Dr. Donald F. Slish at SUNY,
Plattsburgh
32
Crossing-Over Results in Homologous Recombination
33
Holliday Model of Homologous Recombination
34
Meselson-Radding Model of Homologous
Recombination