Mitosis in detail
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Transcript of Mitosis in detail
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05/04
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To Be To Be Answered…Answered…THINK:
How many cells are you composed of?
When an organism grows bigger do you get more cells or just bigger cells or both?
When do your cells divide the fastest? Slowest?
Do cells ever stop dividing?
Are all cells capable of division and replacement?
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Why Would a Cell Why Would a Cell Divide?Divide? As cells absorb nutrients and get larger,
the volume of the cell increases faster than the surface area
This means that a cell can no longer absorb nutrients and get rid of wastes fast enough to support its demands (volume)
So what’s a cell to do?
Solution: divide in 2!
Surface area for exchange not great enough to support cell’s needs
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When Would a Cell When Would a Cell Divide?Divide? Growth
Repair or Replacement
Cancer
Different cells divide at different rates:
Most mammalian cells = 12-24 hours
Some bacterial cells = 20-30 minutes
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Getting Older…Getting Older… All cells are only allowed to complete a
certain number of divisions
Then they die (programmed cell death)
How does cell division change over a lifetime?
Childhood = cell division > cell death
Adulthood = cell division = cell death
The Later Years = cell division < cell death
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Stages of the Cell Stages of the Cell CycleCycle 2 stages = interphase (growth &
replication of DNA) & mitotic phase (division of cell into 2 daughter cells)
Cell spends about 90% of the time in interphase
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InterphaseInterphase Divided into 3 phases:
G1 (1st gap) = small cell is absorbing nutrients, growing & doing its job (i.e. making proteins)
S (synthesis) = cell is continuing to grow & duplicates its DNA (i.e. chromosomes) in preparation for making duplicate cells during mitosis
G2 (2nd gap) = cell keeps growing & doing its job (i.e. making proteins); prepares for cell division; it grows too big…solution = divide in 2
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Mitosis: A Closer LookMitosis: A Closer Look
Prior to entering the mitotic phase, the cell has just come out of interphase
Replicated DNA during S (synthesis)
2 complete sets of chromosomes that must be distributed equally between 2 cells = mitosis
Interphase
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The Mitotic PhaseThe Mitotic Phase Equal distribution of 2 sets of chromosomes
(DNA) into 2 identical daughter cells
Divided into 4 stages of Mitosis:
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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Cell Cycle TidbitsCell Cycle TidbitsHow long is one cell cycle?
Depends on the cell- skin cells = ~24 hours, nerve cells = never after maturity, cancer cells = very short
Remember: every cell only has a certain # of divisions it can undergo, then it dies = apoptosis (programmed cell death)
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ProphaseProphase
Chromatin condenses visible chromosomes
Appear as sister chromatids held together by centromere
Nuclear membrane dissolves
The centrioles migrate to opposite poles & spindle fibers form between them
http://www.biostudio.com/demo_freeman_dna_coiling.htm
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MetaphaseMetaphase
Chromosomes line-up on the metaphase plate
Centromeres are attached to spindle fibers
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AnaphaseAnaphase
Centromeres divide
Spindle fibers contract
Result = sister chromatids are pulled away from one another towards the poles
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TelophaseTelophase
The chromosomes reach the poles
Nuclear membranes form around the 2 new nuclei
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CytokinesisCytokinesis The cytoplasm
distributed equally between the 2 new cells
In animals, a cleavage furrow forms from outside in
In plants, a cell plate forms from inside out
PlantAnimal
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What Mitosis Actually Looks What Mitosis Actually Looks LikeLike
InterphaseProphase Metaphase
Anaphase Telophasehttp://www.sci.sdsu.edu/multimedia/mitosis/mitosis_gif2.html
http://science.nhmccd.edu/biol/bio1int.htm
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Summary of MitosisSummary of Mitosis
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What Happens After What Happens After Mitosis?Mitosis?
The cell returns to interphase
Chromosomes uncoil back into chromatin
The cycle repeats itself over & over…
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At What Stage Are Our Cells At In The Cell At What Stage Are Our Cells At In The Cell Cycle?Cycle?
Different cells can be in different stages
Interphase
Mitosis:
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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Can You Identify the Stages of Can You Identify the Stages of Mitosis?Mitosis?
Put the following mitosis stages in the correct sequence
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The GuarenteeThe Guarentee
The product of mitosis is 2 cells
The daughter cells are identical to each other & to the mother cell
Mother cell
Identical daughter
cellsWhy is this so important?
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The Daughter CellsThe Daughter Cells
In humans, the 2 daughter cells will have 46 chromosomes (23 pairs)
1 chromosome originally from mom & 1 from dad
Each chromosome is said to have the same gene sequence
Identical daughter
cells
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The Beauty of Asexual The Beauty of Asexual ReproductionReproduction
Mitosis is a form of asexual reproduction
New individuals are produced by 1 parent & thus, are identical to their parent
Mother cell
Identical daughter
cells
Runners produces by strawberries
Cuttings from plants
Budding by hydra & yeast