Why do Cells Need to Grow? Replace old cells Replace damaged cells Make new life.
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Transcript of Why do Cells Need to Grow? Replace old cells Replace damaged cells Make new life.
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Why do Cells Need to Grow?
• Replace old cells• Replace damaged cells
• Make new life
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When do Cells Grow?• Cells grow, or more accurately, divide to stay
small• Cells need to be small to function properly– Cellular organelles need to be able to
communicate to each other and the outside world
• The surface area to volume ratio needs to be high– That means, the cell needs more membrane and
less cytoplasm
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The Cell Cycle• The cycle of growing and dividing of eukaryotic cells• It is a continuous production of new cells• Controlled by a series of signals
Three Main Stages of the Cell Cycle:1. Interphase
2. Mitosis3. Cytokinesis
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Interphase- The Longest Stage
Broken down into Three Sub-Stages
1. G1 Sub-Stage• Period of cell growth and maturing into a
functioning cell• Some cells, like muscle cells, stop here
2. S Sub-Stage• Duplicates its DNA • DNA is copied to put into new cell
3. G2 Sub-Stage• Prepares for Division• Cell gets ready to divide
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Mitosis and Cytokinesis
• Mitosis– When the nucleus and
cellular material divides
• Cytokinesis– When the cell’s
cytoplasm divides
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MitosisThe accurate separation of the cell’s DNA
1. Prophase2. Metaphase3. Anaphase4. Telophase
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Prophase• Longest phase of Mitosis• The copied DNA condenses into
chromosomes– Chromosomes are shaped like an X– The center of the X is called the
centromere– The pair of chromosomes are
called sister chromatids• Nuclear membrane disintegrates • Spindle fibers (microtubules)
begin to form
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Metaphase
• Chromosomes attach to spindles (microtubules)
• Chromosomes align along the equator of the cell
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Anaphase
• The microtubules of the spindles begin to shorten
• The sister chromatids are pulled apart
• The chromatids are moved to the poles of the cell
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Telophase
• Chromosomes reach end of cell
• Nuclear membrane reappears
• Chromosomes decondense
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Cytokinesis
• Division of the cytoplasm
• Animal cells – furrow
• Plant cells – cell plate
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Cell Cycle Checkpoints
• The cell cycle has “checkpoints”• “security” proteins at the “checkpoints”• If something goes wrong, cell cycle stops• Also regulation on when cell cycle starts and
stops• What is it called when the cell cycle continues
uncontrollably?