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Chapter 3 Lesson 1
THE CELL CYCLE AND DIVISION
The Cell Cycle
The cell cycle is the cycle of growth, development, and
division of most cells in an organism.
The cell cycle makes it possible for organisms to
 grow and develop
 replace old or damaged cells, and
 produce new cells.
To reproduce, a cell divides.
Overview
Phases of the Cell Cycle for Eukaryotic Cells
 Interphase
 Mitotic Phase
The Interphase – 3 Stages
 G1, S, and G2
The Mitotic Phase
 2 stages – mitosis followed by cytokinesis
o Phases of Mitosis: Prophase, Metaphase, Anaphase, &
Telophase
Results of Cell Division
 reproduction, growth, replacement, and repair
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Phases of the Cell Cycle for Eukaryotic Cells
NOTE - Only eukaryotic cells undergo mitosis.
1. The interphase
 This is the period of the cell’s growth and
development.
2. The mitotic phase (when mitosis takes place)
 This is the cell’s reproduction.
Length of a Cell Cycle
 The length of time for a cell to complete the cell
cycle depends on the type of cell.
 It may be a few minutes or even a year.
 Most dividing human cells take about 24 hours.
The Interphase
 A cell spends most of its life in the interphase.
 The cell grows and prepares for cell division.
 The interphase has 3 stages.
Three Stages of the Interphase
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1. The G1 Stage (the longest part of the interphase)
 Rapid growth takes place.
 Organelles are replicated.
 Normal cell functions occur.
o For example – stomach cells produce and put
out digestive enzymes.
 The DNA is in the form of long, thin strands called
chromatin.
2. The S Stage
 More growth takes place.
 Organelles are replicated.
 Chromosomes are replicated in the nucleus.
o The cell’s DNA is copied.
o The DNA is arranged as pairs of identical
chromosomes called sister chromatids.
o Sister chromatids are held together by a
structure called the centromere. (See p. 88.)
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3. The G2 Stage
 More growth, organelle replication, and cell
functions occur.
 The cell stores energy that will be needed for cell
division.
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The Mitotic Phase
 It follows the interphase.
 It produces a pair of daughter cells.
 It occurs in two stages:
1. Mitosis
o During mitosis the nucleus divides into two
identical nuclei.
o Mitosis occurs in four phases.
2. Cytokinesis
o The cytoplasm divides with its contents,
including the organelles.
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Phases of Mitosis
The process is continuous, but 4 phases are observed.
1. Prophase
 Duplicated chromosomes are present.
 The nucleolus disappears and the nuclear
membrane breaks down.
 Spindle fibers form.
2. Metaphase
 Spindle fibers cause chromosomes to line up in a
single file in the middle of the cell.
3. Anaphase
 Sister chromatids separate.
 Spindle fibers shorten and pull chromatids in
opposite directions.
o This leads to two separate identical sets of
single-stranded chromosomes.
 Cell lengthens.
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4. Telophase
 A nuclear membrane forms around each set of
chromosomes in the two sides of the elongated cell.
o This gives two new & identical nuclei.
 Spindle fibers begin to break down.
After Mitosis: Dividing the Cell’s Components
Cytokenisis is the process of the cell’s cytoplasm being
divided.
For Animal Cells
 The cell membrane contracts (squeezes together) to
form a furrow in the middle of the cell.
 The furrow gets deeper until two separate cells
form.
For Plant Cells
 Vesicles join to form a disk, called a cell plate, down
the middle of the cell.
 The cell plate grows toward the cell wall, forming a
new cell wall.
 This results in two new daughter cells.
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Results of Cell Division
The cell cycle is important for:
1. reproduction in some organisms
2. growth in multicellular organisms
3. replacement of worn out or damaged cells, and
4. repair of damaged tissues.
• In some unicellular organisms, cell division is a form of
reproduction.
• Cell division allows multicellular organisms to grow and
develop from one cell.
Fun Facts
Each species has a characteristic number of
chromosomes in each cell.
Species
Chromosomes
human cell
46
guinea pig cell
64
gorilla cell
48
apple cell
34