Cell Reproduction
Why Do Cells Divide???
• DNA Overload - information overload too much cell to make proteins for.
• Materials Exchange Problem – Surface Area to Volume Ratio
• Injury
• Depletion of Cells from natural death.
Human Chromosomes23 Homologous Pairs
homologous pairs= a matching pair of chromosomes, one from each parent
Chromosomes
• Number of chromosomes depends on characteristics of species
• Examples: • Humans 46 (23 pr)
Earth worm 36 (18pr)• Fly 8 ( 4 pr)
Time for cell divisiondepends on type of cellbacteria completes cycle in 22 minutes
nerve cell some only once in entire life
liver cell may take 1 year
G1 ~ intense activity & cell growthS phase ~ DNA replication ( will copy every chromosome)G2 ~ prepares for mitosis usually shortest part of interphase organelles needed for mitosis are made now
Go to Video Clips
Stages of Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
• Mitosis begins (cell begins to divide)
• Centrioles (or poles) appear and begin to move to opposite ends of the cell.
• Spindle fibers form between the poles.
All these cells are in prophase
Metaphase
• Chromosomes line up at the equator of the cell.
• Animal cell Plant Cell
Spindle fibers attach to the chromatids
Anaphase ~ Chromatids (or pairs of chromosomes) separate and
begin to move to opposite ends of the cell.
Animal Cell Plant Cell
TelophaseTwo new nuclei form.
Chromosomes appear as chromatin (threads rather than rods).
Mitosis ends.Animal Cell Plant Cell
CytokinesisCell membrane moves inward to
create two daughter cells – each with its own nucleus with identical
chromosomes.
Division of
Prokaryotic Cells
(binary fission)
http://www.biologycorner.com/resources/mitosis-animated.gif
MorePractice
Cell Cycle
In lab, we will be looking at the tip of a plant leaf, looking for the
different stages of mitosis
end
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