Chapter 3 Lesson 1
The Cell Cycle and Cell Division
The Cell Cycle
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Cell Cycle- most cells in an organism go through a cycle of
growth, development, and cell division.
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Organisms Grow
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Organisms Develop
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Organisms Replace Old and Damaged Cells
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Organisms Produce New Cells
Phases of the Cell Cycle
Two Main phases
 Interphase
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A cell spends most of its life in interphase
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Rapid growth and replication ( copying) of its membrane
bound organelles
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Copying DNA
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Preparation for cell division
Mitotic Phase
Mitotic Phase
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A Cell reproduces at this time
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It has two phases
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Nucleus divides in the first stage
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Cell’s cytoplasm divides in the second stage
End product of mitosis is two identical daughter cells
Length of the cell cycle
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Depends on the type of cell dividing
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Eukaryotic cells have many membrane- bound organelles
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Some cells it may last 8 minutes
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Some cells it may take as long as a year
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Most human cells take 24 hours
Interphase
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The cell rapidly grows
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Increase in cellular activities like making proteins
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Actively dividing cells make copies of their DNA
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The DNA is called chromatin
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It resembles spaghetti because it is long strands of chromatin are tangled together
Interphase cont.
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G1 stage- Period of rapid growth, longest period of interphase
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S stage- continues to grow, it also copies its DNA
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G2- final period before the cell divides, also a period of growth
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Each organelle is also replicated or copied
Mitosis
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The nucleus and the cells contents (organelles) divide
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Divided into 4 stages
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Prophase
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Metaphase
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Anaphase
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Telophase
Prophase
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The copied chromatin coils together
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Chromosomes begin to appear
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Nucleolus disappears
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The nuclear membrane dissolves
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The spindle fibers begin to form
Metaphase
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The chromosomes line up in the middle of the cell
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The spindle fibers attach to the centrioles and the centromeres
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Shortest phase of mitosis
Anaphase
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The two sister chromatids in the chromosomes separate
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The spindle fibers pull them apart in opposite directions
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The cell begins to lengthen ( become longer or more oval in shape)
Telophase
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The spindle fibers begin to disappear
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Chromosomes begin to uncoil
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Nuclear membrane forms around each set of chromosomes forming a new
nucleus
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Spindle fibers begin to disappear
Cytokinesis
Animal Cell
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Cells cytoplasm divides
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In animal cell
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Cell membrane contracts around the middle of the cell
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A furrow forms
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The furrow gets deeper until the cell membrane comes together to divide the cell
In plant cell
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A new cell wall forms in the middle of the plant cell
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A cell plate forms and grows outward until a new cell wall is formed.
Plant cell
Results of cell division
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Two identical daughter cells are formed
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Reasons for cell division
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Reproduction- some unicellular organisms reproduce this way
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Growth- growth of an organism is dependent on mitosis
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Replacement- cells in the skin are constantly being replaced
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Repair- when a bone breaks or you cut your skin