Homologous Chromosomes Homologous Chromosomes Sister

Home , Sister chromatids

Origin of Bacterial chromosome: replication Double-stranded DNA

Septum

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Chromosome Rosettes of Chromatin Loops Chromatin Loop Solenoid Scaffold protein Scaffold protein

Chromatin loop

DNA Double Helix (duplex) Nucleosome Histone core DNA

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Kinetochore

Replication

Cohesin Centromere proteins

Kinetochores

Sister chromatids Sister chromatids

Metaphase Prometaphase Anaphase Prophase Telophase Cohesin Chromatid proteins G2 Centromere region of

G1 chromosome S Interphase

G2 Mitosis M Phase Cytokinesis S G1 Kinetochore Kinetochore microtubules Metaphase chromosome 7 8

INTERPHASE G MITOSIS CYTOKINESIS 2 Prophase Prometaphase Metaphase Anaphase Telophase Polar 57 µm microtubule Centrioles 80 µm 80 µm 80 µm 80 µm Chromosomes 80 µm 80 µm (replicated; 80 µm Chromatin aligned on Kinetochore Polar animal Mitotic spindle Condensed Centromere and Mitotic Kinetochore (replicated) metaphase plate microtubule microtubule Chromosomes cells only) beginning to form chromosomes kinetochore spindle Nucleus reforming microtubule Centrioles Aster Kinetochore microtubule

Cleavage furrow Nuclear Nucleolus Kinetochore Polar microtubule membrane Nucleus • Chromosomes condense and • Chromosomes attach to microtubule become visible microtubules at the kinetochores • Chromosomes appear as two Polar microtubule • Proteins holding centromeres of • Chromosomes are clustered at • In animal cells, cleavage furrow • DN A has been replicated • Each chromosome is oriented sister chromatids held together sister chromatids are degraded, opposite poles and decondense forms to divide the cells • Centrioles replicate (animal cells) such that the kinetochores • All chromosomes are aligned at the centromere freeing individual chromosomes • Nuclear envelopes re-form around • In plant cells, cell plate forms • Cell prepares for division of sister chromatids are at equator of the cell, called • Cytoskeleton is disassembled: attached to microtubules the metaphase plate • Chromosomes are pulled to chromosomes to divide the cells spindle begins to form from opposite poles. • Chromosomes are attached opposite poles (anaphase A) • Golgi complex and ER re-form • Golgi and ER are dispersed • Chromosomes move to to opposite poles and are • Spindle poles move apart • Nuclear envelope breaks down equator of the cell under tension (anaphase B)

Metaphase

Pole Overlapping Pole microtubules

Late Anaphase

Prokaryotes Some Protists Other Protists Yeasts Animals

No nucleus, usually Nucleus present and A spindle of micro- Nuclear envelope Spindle microtubules have single circular nuclear envelope tubules forms between remains intact; spindle begin to form between chromosome. After DNA remains intact during two pairs of centrioles at microtubules form inside centrioles outside of is replicated, it is cell division. opposite ends of the the nucleus between nucleus. Centrioles move partitioned in the cell. Chromosomes line up. cell. The spindle passes spindle pole bodies. A to the poles and the After cell elongation, Microtubule fibers pass through one tunnel in single kinetochore nuclear envelope breaks FtsZ protein assembles through tunnels in the the intact nuclear microtubule attaches to down. Kinetochore into a ring and facilitates nuclear membrane and envelope. Kinetochore each chromosome and microtubules attach 0.7 µm septation and cell set up an axis for microtubules form pulls each to a pole. kinetochores of division. separation of between kinetochores chromosomes to spindle replicated on the chromosomes poles. Polar microtubules Chromosome chromosomes, and cell and the spindle poles Kinetochore microtubule extend toward the center Vesicles containing Cell wall division. and pull the chromo- of the cell and overlap. FtsZ protein somes to each pole. Spindle pole body membrane components Nucleus Microtubule Kinetochore microtubule fusing to form cell plate Chromosome Kinetochore microtubule Fragments Central spindle of nuclear of microtubules envelope

Septum

Polar microtubule

Nucleus

Centrioles Kinetochore Centriole Polar microtubule

G2/M checkpoint Spindle checkpoint

High M MPF activity Cyclin G2 Concentration

G1/S checkpoint G Low S (Start or restriction point) 1

G2 M G1 S G2 M G1 S G2 M

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G2/M Checkpoint Spindle Checkpoint

• Replication • Chromosomes P completed attached at Cyclin-dependent kinase • DNA integrity metaphase plate (Cdk) M

G1/S Checkpoint

Cdk1/Cyclin B Cyclin • Growth factors • Nutritional state G P S of cell 1 • Size of cell

G2/M Checkpoint Spindle Checkpoint Cdk1/Cyclin B APC Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Replication • Chromosomes completed attached at p53 allows cells with p53 repaired DNA to divide. • DNA integrity metaphase plate protein

DNA repair enzyme M Normal p53 1. DNA damage is caused by 2. Cell division stops, and p53 triggers 3. p53 triggers the destruction of heat, radiation, or chemicals. enzymes to repair damaged region. cells damaged beyond repair. G2

G1/S Checkpoint Abnormal p53 protein Cancer cell Cdc2/G1Cyclin

• Growth factors • Nutritional state 2. The p53 protein fails to stop cell 3. Damaged cells continue to divide. G Abnormal p53 1. DNA damage is caused by of cell 1 division and repair DNA. Cell divides If other damage accumulates, the S heat, radiation, or chemicals. • Size of cell without repair to damaged DNA. cell can turn cancerous.

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