Transcript The Cell Cycle - Lake Stevens High School / Overview

Chapter 12
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Described by Rudolf Virchow in 1855.
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involves the distribution of genetic material
(chromosomes) from parent to daughter cell
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Functions
◦ reproduction of an entire organism (singlecelled)—asexual reproduction
◦ Allows multicellular organisms to develop
from a single cell
◦ renewal and repair (replacing dead cells and
healing wounds)
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life of a cell from time it was
split from parent cell until it
divides into two daughter cells
Different in cell types
◦ Prokaryotes
 Binary fission
◦ Eukarytotes--somatic cells
(body cells)
 mitosis (identical cells)
◦ Eukaryotes--gametes (sperm
and egg)
 meiosis (non-identical cells)
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DNA exists as chromatin
in cells not undergoing
division (mitosis)
During mitosis
chromatin condenses
into chromosomes
Duplicated chromosome
= sister chromatid
◦ attached at centromere
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Interphase
◦ 90% of the cell cycle
◦ divided into:
 G1 “growth/gap 1” (grow)
 S “synthesis” (chromosomes copied)
 G2 “growth/gap 2” (grow and prepare for division)
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Mitotic (M) Phase (mitosis)--division of genetic material
◦ prophase- chromosomes condense (sister chromatids),
mitotic spindle forms, centrosomes (centrioles) migrate
to opposite ends
◦ prometaphase- nuclear membrane disappears,
microtubules (spindle fibers) begin to attach to
chromatids (centromere/kinetochore)
◦ metaphase- chromosomes line up on metaphase plate
(middle of cell), all microtubules attached to chromatids
◦ anaphase- chromatid pairs are pulled apart and move
toward opposite ends of cell
◦ telophase- two nuclei begin to form, chromosomes
unwind, cytoplasm begins to pinch inward (cleavage)
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Cytokinesis--complete division of cytoplasm
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Frequency of cell division varies with cell type,
which is crucial to normal growth, development
and maintenance
Cell cycle regulated at certain checkpoints by
internal and external signals.
◦ a “stop and go” signal which regulates the cycle
 Allows the cell to determine if there is enough
nutrients and raw materials to move to the next
phase of the cycle
◦ located in G1, G2, and M phases
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In Eukaryotes, cellular reproduction must be
controlled to maintain the form and function
of different parts of the body
◦ Prokaryotes reproduce constantly when
environmental conditions are optimal
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Progression through the phases of the cell
cycle is tightly regulated
Some cells never reproduce and enter G0
phase, a “non-dividing” phase
◦ Cells may be here for a designated period of time
or forever…
 Nerve and muscle cells
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G1 checkpoint triggered by DNA damage
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S checkpoint triggered by incomplete DNA
replication
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G2 checkpoint triggered by DNA damage
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M checkpoint triggered by chromosome not
attaching to spindle
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Regulatory Molecules
◦ protein kinases
 enzymes that activate or inactivate
other proteins by phosphorylation;
help in cell signaling
 “go” signals in G1 and G2
◦ cyclins
 Proteins that activate the kinases by
attaching (cyclin-dependent kinases-Cdks)
 Allosteric regulation
 levels rise and fall in response to
concentration of kinase
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MPF (maturation/mitosis promoting factor): triggers
passage into M-phase. Concentration declines as mitosis
proceeds, eventually stopping mitosis
◦ PDGF (platelet derived growth factor): produced in
blood (platelets), helps stimulate connective tissue
to heal after injury
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Regulatory mechanisms are missing in cells (due to
mutations)
Cells divide excessively and become invasive; “faulty cell
cycle control”
◦ benign vs. malignant tumors
◦ chemotherapy alters cell cycle (prevents it from
occurring), but targets cancerous as well as normal cells
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can stop dividing at random points in cell cycle, or can be
“immortal” and divide indefinitely
◦ HeLa Cells