12/9/14 objective: what is the structure of a chromosome and what is its role in the cell cycle? do...
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12/9/14
Objective: What is the structure of a chromosome and what is its role in the cell cycle?
Do Now: How many cells does mitosis produce?
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Cell Division: 1 cell divides into 2 identical DAUGHTER cells
Getting from there to here…
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• For reproduction – asexual reproduction
• one-celled organisms
• For growth– from fertilized egg to
multi-celled organism
• For repair & renewal– replace cells that die
from normal wear & tear or from injury
Why do cells divide?
amoeba
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Nucleus Cell
Chromosomes
Chromosomes are made of DNA!!
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• Thread-like structures found in the nucleus of cells that contain DNA
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• A combination of DNA and protein that make up a chromosome
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The Cell Cycle
Interphase
• 90% of cell cycle• cell doing its “everyday job”• makes proteins, etc Prepares for duplication if triggered
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• Interphase can be divided into subphases– G1 phase
– S phase
– G2 phase
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Interphase• Divided into 3 phases:
– G1 = (Growth)• cell grows
– S = DNA Synthesis• copies chromosomes
– G2 = (Growth)• prepares for division • cell grows (more)
G0
signal to
divide
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double-strandedmitotic humanchromosomes
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Mitotic PhaseMitotic Phase
- Stage where the cell is actually dividing
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• Before you can share your notes,
You have to
make
a copy
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- Chromatin condenses- Can see sister chromatids - Nuclear membrane breaks down- Spindle fibers form
Prophase
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Prophase
• Protein fibers cross cell to form mitotic spindle– coordinates movement of
chromosomes
Microtubules: protein fibers that make up the spindle
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- Sister Chromatids: two identical joined chromosomes
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- Centromere: the region where the 2 chromatids are joined together
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Metaphase • Chromosomes align along
middle of cell– metaphase plate
• meta = middle plane
– spindle fibers coordinate movement
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Anaphase • Sister chromatids separate
– move to opposite poles
– pulled at centromeres
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Telophase• Chromosomes arrive at
opposite poles– Nuclear membrane
reforms– Chromosomes disperse
• no longer visible under light microscope
• Spindle fibers disperse
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Cytokinesis• Animals
• Splitting of cytoplasm• cleavage furrow forms
(shallow groove near old metaphase plate)
• splits cell in two
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Cytokinesis in Animals
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Mitosis in whitefish blastula
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Cytokinesis in Plants• Plants
– cell plate forms new cell wall
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The Cell Cycle Control System• The sequential events of the cell cycle
– Are directed by a distinct cell cycle control system, which is similar to a clock
Control system
G2 checkpoint
M checkpoint
G1 checkpoint
G1
S
G2M
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• The clock has specific checkpoints– Where the cell cycle stops until a go-ahead signal is
received
G1 checkpoint
G1G1
G0
(a) If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
(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 nondividing state.
G0 phase: a non-dividing state
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Fig. 12-15
G1
G0
G1 checkpoint
(a) Cell receives a go-ahead signal
G1
(b) Cell does not receive a go-ahead signal
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Cancer
• A disease caused by the disruption of the mechanism that normally controls the cell cycle
• Leads to uncontrolled cell divison
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Tumor
• A mass produced by out-of-control cell reproduction
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Types of Tumors
Benign tumor: An abnormal mass of normal cells that can usually be removed by surgery
Malignant tumor: masses of cells from the reproduction of cancer cells (can spread if not removed or killed)
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Metastasis
The spread of cancer beyond their original site
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Prevention/Early Detection/Treatment
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Getting Started
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Interphase
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Prophase
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Metaphase
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Drawing Metaphase
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Anaphase
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Telophase
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Cytokinesis