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Chapter 9 The Cell Cycle
9
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(the letters/
sequences that makes DNA)
 Chromatin: the complex of DNA and proteins that makes up eukaryotic chromosomes
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(Many chains of DNA compressed)
 Chromosome: A cellular structure consisting of one DNA molecule and associated protein
molecules
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A prokaryotic cell often has a single, circular chromosome, which is found in the
nucleoid, a region that is not enclosed by a membrane
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When this cohesion is broken, the
chromatids separate during cell division, becoming
the chromosomes of the new daughter cells
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]

 Meiosis: a modified type of cell division in sexually reproducing organisms consisting of
two rounds of cell division but only one round of DNA replication
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2 The mitotic phase alternates with interphase in the cell cycle
Phases of the Cell Cycle
1
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Mitosis: PPMAT (Preparing to Painting My Ass Turquoise)
1) Prophase: Chromatin condenses into chromosomes - nucleolus disappears –
mitotic spindles being to form – the centrosomes move away from each other to
opposite sides of the cell
2) Pro-metaphase: Nuclear membrane breaks down – Kinetochore microtubules
invade nuclear space and attach to kinetochores – Polar microtubules push against
each other moving centrosomes apart – nuclear envelope fragments 3) Metaphase: centrosomes are now at opposite ends of the cell - chromosomes line
up along the metaphase plate (imaginary plate) – cleavage furrows
4) Anaphase: Chromosomes break at centromeres - sister chromatids move to
opposite ends of the cell – the cell elongates as the non-kinetochore microtubules
lengthen 5) Telophase: Mitotic spindles disappear/ depolymerized – 2 daughter nuclei form in
the cell - cell divides into two - Cell membrane reforms – Myosin II and actin
filament ring contract to cell
into two
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–
cytoplasm divides  Myosin: a fibrous
protein that forms the
contractile filaments of
muscle cells and is also
involved in motion in other
types of cells

 Actin: a proteins that forms (together with myosin) the contractile filaments of muscle cells,
and is also involved in motion in
other types of cells
The Mitotic Spindle: A Closer
Look

The mitotic spindle is
an apparatus of microtubules that
controls chromosome movement
during mitosis
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 Some
spindle microtubules attach to the
kinetochores of chromosomes
and move the chromosomes to
the metaphase plate
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 Meanwhile, motor proteins push non-kinetochore
microtubules from opposite poles away from each other, elongating the cell
...

 Mitotic Spindle: An assemblage of microtubules and associated proteins that is involved in
the movement of chromosomes during mitosis
 Centrosome: In a duplicated chromosome, the region on each sister chromatid where they
are most closely attached to each other by proteins that bind to specific DNA sequences ;
this close attachment causes a constriction in the condensed chromosome
 Aster: a radical array of short microtubules that extends from each centrosome toward the
plasma membrane in an animal cell undergoing mitosis structure of proteins attached to
the centromere that links each sister chromatid to the mitotic spindle
 Kinetochore: A structure of proteins attached to the centromere that links each sister
chromatid to the mitotic spindle
Cytokinesis: A Closer Look
 Mitosis is usually followed by cytokinesis
...

 Cleavage: the process of cytokinesis in animal cells, characterized by pinching of the plasma
membrane  the succession of rapid cell divisions without significant growth during early
embryonic development that converts the zygote to a ball of cells 
 Cleavage Furrow: the first sign of cleavage in an animal cell; a shallow groove around the
cell in the cell surface near the old metaphase plate
 Cell Plate: a membrane bounded, flattened sac located at the midline of its parts by
centrifugation at successively higher speeds
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 Some of the proteins involved in bacterial binary
fission are related to eukaryotic actin and tubulin
...

 Binary Fission: a method of asexual reproduction by division in half
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 Origin of Replication: site where the replication of a DNA molecule begins, consisting of a
specific sequence of nucleotides
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3 The eukaryotic cell cycle is regulated by a molecular control system
 The timing and rate of cell division in different parts of a plant or animal are crucial to normal
growth, development, and maintenance
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Loss of Cell Cycle Control in Cancer Cells
Cancer cells elude normal cell cycle regulation and divide out of control, forming
tumors
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
 Malignant tumors: a cancerous tumor containing cells that have significant genetic and
cellular changes and are capable of invading and surviving in new sites
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 Metastasis: the spread of cancer cells to locations distant from their original site



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