why does a cell divide?
DESCRIPTION
Why does a cell divide?. Cell cycle. G1 phase: Growth, cytokinesis finishes , protein synthesis, prepares to copy DNA S phase: DNA copies itself G2: protein synthesis continues prepares to divide M Mitosis Nucleus divides perfectly Cytokinesis: cytoplasm divides sort of evenly. - PowerPoint PPT PresentationTRANSCRIPT
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Why does a cell divide?
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Cell cycle
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• G1 phase: Growth, cytokinesis finishes , protein synthesis, prepares to copy DNA
• S phase: DNA copies itself• G2: protein synthesis continues prepares to
divide• M Mitosis Nucleus divides perfectly• Cytokinesis: cytoplasm divides sort of evenly
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Unicellular organisms
• Mitosis is reproduction• Nutrients, oxygen come in across the cell membrane.
Waste products leave through the cell membrane.• The ability to maintain a chemical balance across the
cell membrane is vital.• As the cell grows the volume increases faster than
the surface area of the membrane.• When the cell can no longer maintain the traffic
across the membrane. It signals the cell to divide.
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Multicellular Organisms
• If cells are limited to their size then in order to have large organisms they become multicellular.
• Cells specialize into tissues each with a certain job. Nerves for communication and sensing, muscles for moving, digestive system for attaining food etc.
• Each of these cells contain all the DNA but to specialize they turn off certain genes and turn on others.
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How do cells divide?Mitosis and cytokinesis
• Mitosis• How the nucleus divides exactly• Uncoiled DNA copies itself (Chromatin threads)• DNA coils up (Chromosomes)• Centrioles go to each end of the cell • Micro tubules attach to chromosomes• Microtubules pull them apart • Mitosis - YouTube
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Phases of mitosis
• Prophase coil up
• Metaphase line up
• Anaphase separate
• Telophase uncoil
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Cytokinesis
• Cytoplasm divides
• At the end of telophase
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Interphasecell does it’s work
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Intephase
Onion root tip White fish ovaries
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Prophase cell prepares to divide
Early prophase Late Prophase
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Prophase
• DNA coils up into Chromosomes• Centrioles migrate to the 2 poles
• Aster starts to form
• Nuclear envelopes disintegrates• Chromosome are doubled in
chromatid pairs.
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Prophase
In allium root tip In white fish ovaries
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Metaphase Chromosomes line up
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Metaphase
• Centrioles form a complete spindle • Microtubules attach to the kinetichores of the
chromatid pairs• Chromatid Pairs line up across the equator .• Nuclear membrane is gone
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Metaphase
In allium root tip In white fish
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Anaphase the chromotids separate
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Anaphase
• The micro tubules shorten and pull the chromatids apart.
• The chromatids migrate to opposite ends of the cell
• The micro tubules push the cell membrane make the cell longer
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Anaphase
In allium root tips In white fish ovaries
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Telophasetwo new nuclei reform
Early telophase Late telophase
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Telophase
• This is prophase backwards• The nuclear envelope reforms.• The chromosomes uncoil• The aster disappears• The cytoplasm starts to divide
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Telophase
In allium root tips In white fish ovaries
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Cytokinesiscytoplasm divides
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Animal cells make a cleavage furrow
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Plant cells make a cell plate
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Cytokinesis
Allium root tip White fish ovaries
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All the stages of mitosis in Allium root tips