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Chapter 12: The Cell Cycle
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Chapter 12: The Cell Cycle
1.
When is cell division important?
-
Reproduction – unicellular organisms – binary fission in bacteria
Growth & development from fertilized egg
Repair (& replacement) of damaged cells
100 µm
(a) Reproduction. An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).
200 µm
20 µm
(b) Growth and development.
(c) Tissue renewal. These dividing
This micrograph shows a
bone marrow cells (arrow) will
sand dollar embryo shortly after
give rise to new blood cells (LM).
the fertilized egg divided, forming
two cells (LM).
Chapter 12: The Cell Cycle
1.
2.
When is cell division important?
What is an organism’s genome?
-
3.
Total hereditary endowment (all genes) in the cell of a species
Nuclear & extra-nuclear (mito & chloro)
How many chromosomes do we have?
46 – somatic cell (cells of the body)
-
23 – gamete (sex cells – sperm & egg)
-
4.
2n
Diploid – 2 sets of chromosomes
n
Haploid – 1 set of chromosomes
What are chromosomes made of?
-
Chromatin
DNA & proteins
Fig 12.4 Chromosome duplication & distribution during cell division
0.5 µm
A eukaryotic cell has multiple
chromosomes, one of which is
represented here. Before
duplication, each chromosome
has a single DNA molecule.
Once duplicated, a chromosome
consists of two sister chromatids
connected at the centromere. Each
chromatid contains a copy of the
DNA molecule.
Mechanical processes separate
the sister chromatids into two
chromosomes and distribute
them to two daughter cells.
Chromosome
duplication
(including DNA
synthesis)
Centromere
Separation
of sister
chromatids
Centromeres
Sister
chromatids
Sister chromatids
Chapter 12: The Cell Cycle
1.
2.
3.
4.
5.
When is cell division important?
What is an organism’s genome?
How many chromosomes do we have?
What are chromosomes made of?
What are the 2 major phases of the cell cycle?
-
Interphase – 90%
Mitotic phase – 10%
INTERPHASE
S
(DNA synthesis)
G1
G2
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Chapter 12: The Cell Cycle
1.
2.
3.
4.
5.
When is cell division important?
What is an organism’s genome?
How many chromosomes do we have?
What are chromosomes made of?
What are the 2 major phases of the cell cycle?
-
6.
Interphase
Mitotic phase
What are the steps of the cell cycle?
-
IPMAT
Interphase
Prophase
Metaphase
Anaphase
Telophase
Combine pro- & prometaphase
G2 OF INTERPHASE
Centrosomes
(with centriole pairs)
Nucleolus
Chromatin
(duplicated)
Nuclear
Plasma
envelope membrane
PROPHASE
Early mitotic
spindle
Aster
Centromere
PROMETAPHASE
Fragments
of nuclear
envelope
Chromosome, consisting
of two sister chromatids
Chromosomes appear as Pairs
Kinetochore
Nonkinetochore
microtubules
Kinetochore
microtubule
METAPHASE
ANAPHASE
Metaphase
plate
Spindle
Cleavage
furrow
Centrosome at Daughter
one spindle pole chromosomes
Middle
TELOPHASE AND CYTOKINESIS
Apart
Nucleolus
forming
Nuclear
envelope
forming
Two
Chapter 12: The Cell Cycle
1.
2.
3.
4.
5.
6.
7.
When is cell division important?
What is an organism’s genome?
How many chromosomes do we have?
What are chromosomes made of?
What are the 2 major phases of the cell cycle?
What are the steps of the cell cycle?
What is the difference between animal and plant cytokinesis?
-
Animal – cleavage furrow – cell forms from outside in
Plants – cell plate – cell forms from inside out
Figure 12.9 Cytokinesis in animal and plant cells
100 µm
Cleavage furrow
Contractile ring of
microfilaments
Vesicles
forming
cell plate
Wall of
patent cell
1 µm
Cell plate
New cell wall
Daughter cells
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (SEM)
Chapter 12: The Cell Cycle
1.
2.
3.
4.
5.
6.
7.
8.
When is cell division important?
What is an organism’s genome?
How many chromosomes do we have?
What are chromosomes made of?
What are the 2 major phases of the cell cycle?
What are the steps of the cell cycle?
What is the difference between animal and plant cytokinesis?
How is the cell cycle regulated?
-
Checkpoints
Make sure cell has enough “ingredients” to move to next stage
Figure 12.14 Mechanical analogy for the cell cycle control system
G1 checkpoint
Control
system
G1
M
M checkpoint
G2 checkpoint
G2
S
Figure 12.15 The G1 checkpoint
G0
G1 checkpoint
G1
(a) If a cell receives a go-ahead signal at
the G1 checkpoint, the cell continues
on in the cell cycle.
G1
(b) If a cell does not receive a go-ahead
signal at the G1checkpoint, the cell
exits the cell cycle and goes into G0, a
non-dividing state.
Most functioning cells are in G0
Chapter 12: The Cell Cycle
1.
2.
3.
4.
5.
6.
7.
8.
When is cell division important?
What is an organism’s genome?
How many chromosomes do we have?
What are chromosomes made of?
What are the 2 major phases of the cell cycle?
What are the steps of the cell cycle?
What is the difference between animal and plant cytokinesis?
How is the cell cycle regulated?
-
Checkpoints
Make sure cell has enough “ingredients” to move to next stage
Cyclins
Cyclin-dependent kinase (CDK)
MPF
-
maturation promoting factor
Cyclin + CDK = MPF
(a) Fluctuation of MPF activity and
cyclin concentration during
the cell cycle
Relative Concentration
Fig. 12.16 Molecular control of the cell cycle at the G2 checkpoint
G1 S G2 M
MPF activity
G 1 S G2 M
Cyclin
Time
(b) Molecular mechanisms that
help regulate the cell cycle
1 Synthesis of cyclin begins in late S
phase and continues through G2.
Because cyclin is protected from
degradation during this stage, it
accumulates.
5 During G1, conditions in
the cell favor degradation
of cyclin, and the Cdk
component of MPF is
recycled.
Cdk
Degraded
Cyclin
Cyclin is
degraded
4 During anaphase, the cyclin component
of MPF is degraded, terminating the M
phase. The cell enters the G1 phase.
G2
Cdk
checkpoint
MPF
Cyclin
2 Accumulated cyclin molecules
combine with recycled Cdk molecules, producing enough molecules
of MPF to pass the G2 checkpoint and
initiate the events of mitosis.
3 MPF promotes mitosis by phosphorylating
various proteins. MPF‘s activity peaks during
metaphase.
Chapter 12: The Cell Cycle
1.
2.
3.
4.
5.
6.
7.
8.
9.
When is cell division important?
What is an organism’s genome?
How many chromosomes do we have?
What are chromosomes made of?
What are the 2 major phases of the cell cycle?
What are the steps of the cell cycle?
What is the difference between animal and plant cytokinesis?
How is the cell cycle regulated?
What happens when there is a loss of cell cycle regulation?
- Tumors &/or cancer
- Lack of cell division