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Cells from cells:cell division
Video Intro (8:26)
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Why do cells divide?Cells divide for three reasons:
1. Reproduction
Cells reproduce to form new cells through a process called asexual reproduction
One cell divides to produce two new cells, called daughter cells, that are genetically identical to each other and to the parent cell.
when there is only one parent
Examples:
singlecelled organisms: paramecium – binary fission
body cells – mitosis
¢This process by which a parent cell divides into two daughter cells is called cell division.
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2. Repair
Cells divide to replace lost or damaged cells (e.g. cuts, bruises, broken bones), as well as dying/dead cells.
3. Cell Growth
Cells divide when they grow and become too large to function properly.
For cells to grow, the cell membrane allows for the entry of all of the oxygen, water, and nutrients needed by the cell’s organelles.
Most of the materials that pass into or out of the cell occurs through the processes of diffusion and osmosis.
Diffusion is the movement of particles from areas of high concentration to areas of low concentration.
high concentration
low concentration
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•Large cells have a smaller surface area to volume ratio
•Thus…cells too big will not have enough surface area for the diffusion of all the nutrients & oxygen it needs and the elimination of wastes
1cm
1cm1cm
3cm
3cm
3cmSA =
Vol =
Ratio
SA =
Vol =
Ratio
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Osmosis is the movement of water molecules from areas of high water concentration to areas of low water concentration.
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The cell uses the nutrients and water that enters through its membrane to:
1. grow and increase its volume 2. efficiently perform the functions necessary for its survival Eventually, the cell becomes too large to efficiently perform its functions.
At this point, the cell must divide into two smaller cells so that these jobs can still be performed properly.
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Interphase: Getting Ready for Cell division 1. The centriole duplicates so that it has two copies.
Note: During interphase, the chromosomes are still in the form of threadlike structures called chromatin.
1 centriole 2 centrioles
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2. The nucleus makes an exact copy of every chromatin (all 46). This copying process is called DNA replication.
During DNA replication:
• the DNA molecule (chromatin) is replicated, creating two sister chromatids
• the two sister chromatids join together at a point called the centromere
originalDNA
sister chromatidschromosome
chromatin
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Human chromosomes, magnified ~6100x, that is ready to undergo cell division.
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¢The process of DNA replication is very precise, however copying errors can occur.
¢When there are copying errors, they are usually detected and fixed by special “proofreading” and repair proteins.
Now the cell is ready for cell division
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Cell divisionThere are two stages of cell division: 1. Mitosis 2. Cytokinesis Stage 1 of Cell Division: Mitosis
There are four distinct phases of mitosis:
1. prophase
2. metaphase
3. anaphase
4. telophase
Phases of mitosis: Let’s now complete the handout
PMAT
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¢Sister chromatids coil and condense into visible chromosomes.
¢Each centriole begins to migrate toward the opposite ends of the cell.
¢Threadlike tubules called spindle fibers form and extend from the centrioles toward the centromere of each chromosome.
¢The nuclear membrane disintegrates.
1. Prophase
centromere
spindle fibre
fragments of nuclear membrane spindle
fibres
centriole
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¢The centrioles reach the opposite ends of the cell.
¢The chromosomes line up in the centre of the cell along an invisible “equator”.
¢Each centromere has now become attached to two spindle fibres – one from each end of the cell.
2. Metaphase
“equator”
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¢The spindle fibres retract and pull on the centromere of the chromosomes.
This causes the sister chromatids to separate into two identical chromosomes.(Note: Once the chromatids separate, each becomes a chromosome in its own right)
¢The chromosomes are pulled to opposite sides of the cell.
3. Anaphase
identical chromosomes
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¢The chromosomes arrive at opposite ends of the cell.
¢The chromosomes relax and change back into chromatin.
¢The spindle fibres disappear.
¢New nuclear membrane forms around each set of chromatin
¢Cell membrane begins to pinch inward: called cleavage furrow in animal cells cell plate in plant cells
4. Telophase
cleavage furrow
formation of nucleus
nucleolus
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cleavage furrow
cell plate
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Stage 2 of Cell Division: Cytokinesis ¢The cleavage furrow and the cell plate continue to pinch inward and divide the cytoplasm.
Result: The parent cell is physically separated into two new daughter cells. • each has a complete set of chromosomes contain identical genetic information as each other and the parent cell
• Each daughter cell enters its cell cycle and begins to grow.
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Actual cell division footage video
Cell Division Recap 3D video
One more if needed video
Task Handout
