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Bacterial cell
Septum
Bacterial chromosome: Double-stranded DNA
Origin of replication
1 2
3
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Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid
Nucleosome Histone core
Chromatin loop
Scaffold protein Scaffold protein
DNA
DNA Double Helix (duplex)
4
5
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Homologous chromosomes Homologous chromosomes
Sister chromatids Sister chromatids
Centromere
Replication
Kinetochore
Kinetochores
Cohesin proteins Centromere
6
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G1
G2
S Interphase
Mitosis M Phase
Cytokinesis
M Phase
G2
S G1
Metaphase
Prophase Anaphase
Telophase Prometaphase
7
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Chromatid
Kinetochore
Cohesin proteins
Centromere region of chromosome
Metaphase chromosome
Kinetochore microtubules
8
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INTERPHASE G2 Prophase Prometaphase Metaphase Anaphase Telophase
Nucleus Nucleolus
Aster Chromosomes
Polar microtubule
Nucleus reforming
Cleavage furrow
80 µm 80 µm 80 µm
CYTOKINESIS MITOSIS
Centrioles (replicated; animal cells only)
Nuclear membrane
• DN A has been replicated • Centrioles replicate (animal cells) • Cell prepares for division
• Chromosomes condense and become visible • Chromosomes appear as two sister chromatids held together at the centromere • Cytoskeleton is disassembled: spindle begins to form • Golgi and ER are dispersed • Nuclear envelope breaks down
• Chromosomes attach to microtubules at the kinetochores • Each chromosome is oriented such that the kinetochores of sister chromatids are attached to microtubules from opposite poles. • Chromosomes move to equator of the cell
• All chromosomes are aligned at equator of the cell, called the metaphase plate • Chromosomes are attached to opposite poles and are under tension
• Proteins holding centromeres of sister chromatids are degraded, freeing individual chromosomes • Chromosomes are pulled to opposite poles (anaphase A) • Spindle poles move apart (anaphase B)
• Chromosomes are clustered at opposite poles and decondense • Nuclear envelopes re-form around chromosomes • Golgi complex and ER re-form
• In animal cells, cleavage furrow forms to divide the cells • In plant cells, cell plate forms to divide the cells
Polar microtubule
Kinetochore microtubule
Chromatin (replicated)
80 µm 80 µm 80 µm 80 µm
Mitotic spindle beginning to form
Condensed chromosomes
Centromere and kinetochore
Mitotic spindle
Chromosomes aligned on
metaphase plate Kinetochore microtubule
Polar microtubule
Kinetochore microtubule
© Andrew S. Bajer, University of Oregon
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Centrioles
Sister chromatids
Aster
57 µm
Kinetochore microtubule
Metaphase plate
Polar microtubule
© Andrew S. Bajer, University of Oregon
10
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Metaphase
Pole Pole
Pole Pole 2 µm
Overlapping microtubules
Late Anaphase
Overlapping microtubules
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Cell wall Nucleus
0.7 µm
Vesicles containing membrane components fusing to form cell plate
© B.A. Palevits & E.H. Newcomb/BPS/Tom Stack & Associates
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Septum
FtsZ protein
Chromosome
Chromosome Microtubule
Nucleus
Kinetochore microtubule
Centrioles Kinetochore
Polar microtubule
Spindle pole body
Kinetochore microtubule
Centriole
Prokaryotes Some Protists Other Protists Animals
Kinetochore microtubule
Polar microtubule
No nucleus, usually have single circular chromosome. After DNA is replicated, it is partitioned in the cell. After cell elongation, FtsZ protein assembles into a ring and facilitates septation and cell division.
Nucleus present and nuclear envelope remains intact during cell division. Chromosomes line up. Microtubule fibers pass through tunnels in the nuclear membrane and set up an axis for separation of replicated chromosomes, and cell division.
A spindle of micro- tubules forms between two pairs of centrioles at opposite ends of the cell. The spindle passes through one tunnel in the intact nuclear envelope. Kinetochore microtubules form between kinetochores on the chromosomes and the spindle poles and pull the chromo- somes to each pole.
Nuclear envelope remains intact; spindle microtubules form inside the nucleus between spindle pole bodies. A single kinetochore microtubule attaches to each chromosome and pulls each to a pole.
Spindle microtubules begin to form between centrioles outside of nucleus. Centrioles move to the poles and the nuclear envelope breaks down. Kinetochore microtubules attach kinetochores of chromosomes to spindle poles. Polar microtubules extend toward the center of the cell and overlap.
Yeasts
Central spindle of microtubules
Fragments of nuclear envelope
14
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G1 S G2 M G2 M G1 S G2 M
Co
nce
ntr
atio
n
Low
High MPF activity Cyclin
15
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G2
M
S G1
Spindle checkpoint G2/M checkpoint
G1/S checkpoint (Start or restriction point)
16
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Cyclin
P
Cyclin-dependent kinase (Cdk)
P
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• Growth factors
• Size of cell
G2
M
S G1
Spindle Checkpoint APC Cdc2/Mitotic Cyclin
• Chromosomes attached at metaphase plate
• Replication completed • DNA integrity
G2/M Checkpoint
G1/S Checkpoint
Cdk1/Cyclin B
• Nutritional state of cell
18
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• Growth factors
• Size of cell
G2
M
S G1
Spindle Checkpoint APC Cdk1/Cyclin B
• Chromosomes attached at metaphase plate
• Replication completed • DNA integrity
G2/M Checkpoint
G1/S Checkpoint
Cdc2/G1Cyclin
• Nutritional state of cell
19
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1. DNA damage is caused by heat, radiation, or chemicals.
2. Cell division stops, and p53 triggers enzymes to repair damaged region.
3. p53 triggers the destruction of cells damaged beyond repair.
p53 allows cells with repaired DNA to divide.
1. DNA damage is caused by heat, radiation, or chemicals.
2. The p53 protein fails to stop cell division and repair DNA. Cell divides without repair to damaged DNA.
3. Damaged cells continue to divide. If other damage accumulates, the cell can turn cancerous.
DNA repair enzyme
Cancer cell
p53 protein
No
rmal
p53
A
bn
orm
al p
53 Abnormal
p53 protein
20
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