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The Cell Cycle
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Your cells are dividing…• You need new cells for:
– replacing all of the cells that are dying.– Repairing injury– New growth (getting taller/wider)
• Facts:
• You replace all of your skin every 27 days.
• 300 million cells in your body die and must be replaced every minute.
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50,000 of the cells in your body will die and be replaced with new cells,
all while you have been reading this sentence!
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From beginning to end…• The cell cycle begins when the cell is
formed
• Cell grows increase cytoplasm till it can’t hold anymore….or else…
• The cycle ends when the cell divides and forms new cells.
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Before cells divide…1) Before a cell can divide it must make
an extra copy its DNA.
2) This is called Replication -DNA (deoxyribonucleic acid) contains all
the information that tells the cell how to make proteins.
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DNA REPLICATION
• The DNA is normally long and stringy.(chromatin)
• The cell winds up the DNA into chromosomes (chromosome shape of an X).
• The cell has to an entire copy the DNA so that each new cell will have an identical copy of the DNA.
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Chromosome Numbers• Number of chromosomes has nothing to do with
the complexity of organisms.
• Example: Fruit Flies have 8 chromosomes, potatoes have 48 chromosomes, humans have 46 chromosomes, a single cell protozoa 1600, chickens have 78.
• For human we have 46 chromosomes (23 pairs) During Replication the number doubles to 92.
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Making More Prokaryotic Cells
• Bacteria undergo binary fission
• Binary fission is a type of asexual reproduction.
• Binary fission copies the circular DNA and results in two cells that are equal in size.
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Eukaryotic Cells and DNA
• Eukaryotes are usually much larger and more complex than prokaryotic cells.
• The number of chromosomes in the cells of eukaryotes differ depending on the organism
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Human Chromosomes
• Humans have.. 46 chromosomes
• Each pair are made 23 homologous chromosomes pairs.
Karyotype Chromosome Map
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Making More Eukaryotic Cells• Stage 1: Starts just after division
– cytoplasm grows – toward the end the DNA condense and
makes an extra copy. (replication)
• The two copies are called sister chromatids.
• Chromosomes are held together at the centromere. (in the center) Connects all 2 sister chromatids.
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Making More Eukaryotic Cells
• Stage 2: The chromatids separate in a process called mitosis.
• Mitosis ensures that each new cell receives a copy of each chromosome.
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Stages of Mitosis
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
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Interphase
• Before mitosis begins…– The cell grows (cytoplasm) – the chromosomes are
replicated (copied).
• Each chromosome now consists of two chromatids.
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Prophase• The nuclear envelope
breaks apart • Chromosomes
condense to rod-like structures (like an X).
• The centrioles move to opposite sides of the cell
• spindle fibers form between centrioles.
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Metaphase
• Chromosomes line up along the equator (middle) of the cell.
• Each chromosome attaches to a spindle fiber.
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Anaphase• The chromatids
separate
• Chromatids are pulled to opposite sides of the cell by the fibers attached to the centrioles.
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Telophase• The nuclear
membrane forms around the two sets of chromosomes
• Chromosomes unwind, the fibers disappear.
• mitosis is complete.
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Cytokinesis• In plant cells, a cell
plate forms between the two cells (this is will become the cell wall)
• In animal cells a cleavage furrow forms as the two cells pinch apart. Cell Plate
Cleavage furrow
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Cytokinesis• Once mitosis is completed, the cytoplasm splits
in tow.
• This results in two identical cells that are also identical to the original cell from which they were formed.
• After cytokenesis, the cell cycle is complete and they will begin the cell cycle again.
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http://www.sep.alquds.edu/biology/scripts/Biology_english/part_3_4_files/image010.jpg
Stages of Mitosis
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Significance of Cell Division (mitosis and fission)
• Produces 2 cells that are genetically identical to the parent cell.
• In unicellular organisms is asexual reproduction.
• In multicellular organisms: -Primarily--growth and repair
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How are Mitosis and Binary Fission Different? Binary
Fission is…• Is not mitosis (no phases).
• Has no spindle fibers or microtubules of any kind.
• The DNA does not condense into a distinct chromosome