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The Cell Cycle
Why are cells so small??
• What limits the size of a cell??
– Most cells are between .002 - .2 millimeters
What limits the size of a cell?
• Diffusion
– Very fast and efficient over short distances
– Becomes slow and inefficient as the distances
become larger
– Cells would die before nutrients could reach the
organelles if the cell was too big
What limits the size of a cell??
• Surface Area – to – Volume Ratio
– As cell size increases, its volume increases
much faster than surface area
– Example: If cell size doubles, the cell would
require 8 times more nutrients, but the cell
membrane would only increase by 4 times. This
would mean that the cell doesn’t have enough
room (cell membrane) to diffuse.
What limits the size of a cell??
• DNA
– There’s a limit to how fast DNA can make
proteins
– If you have a large cell then the DNA can’t
make proteins fast enough for the cell.
The Cell Cycle
• Cell Reproduction
– One cell (parent cell) reproduces to make 2
identical cells (daughter cells)
– 5 steps in this process
What is Mitosis
• Mitosis is…THE PROCESS BY WHICH A
CELL’S NUCLEUS DIVIDES!
Before Mitosis…
• Interphase
– This phase is broken down into 3 subphases
– G1 = Cell grows in size and organelles replicate
– S = DNA duplicates itself (DNA Replication)
– Chromatin duplicates – long coily strands of DNA that become
wrapped up
– G2 = Rapid Growth before dividing
– Cells spend most of their time in this phase
Interphase
Interphase
Interphase
Interphase
Mitosis
• Prophase
– A.) Chromatin organizes itself into chromosomes
made up of 2 sister chromatids attached by a
centromere
• Sister Chromatids – A chromosome and its
duplicated twin
• Centromere – rubber band structure that
joins the 2 sister chromatids together
Prophase
– B.) Nuclear membrane
breaks down
– Nucleus dissolves
– C.) Centrioles move to
opposite ends of the cell
(poles)
– Centrioles – cylinder
structures that will reel in the
chromatids
– D.) Spindle fibers form
– Spindle fibers – football
shaped set of ropes that will
attach to the centrioles and
the chromatids
– Made of microtubules
Prophase
Prophase
Prophase
Prophase
Prophase
Prophase
Prophase
Mitosis
• Metaphase
– Spindle fibers attach to centrioles and sister
chromatids at their centromeres.
– Chromosomes line up in the middle of the cell
• Line up on the metaphase plate/equator.
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Metaphase
Mitosis
• Anaphase
– The centromeres split apart and the sister chromatids
separate from each other
– The spindle fibers pull the chromatids toward the poles
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Anaphase
Mitosis
• Telophase
–
–
–
–
–
Chromatids reach the poles
Chromosomes unwind
Spindle fibers break down
Nucleus reforms
Cell begins to split
• Cleavage furrow
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
Telophase
After Mitosis…
• Cytokinesis
– Cells Separate
Cytokinesis
The Cell Cycle
What phase is this cell in?
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What phase is this cell in?
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What phase is this cell in?
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What phase is this cell in?
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What phase is this cell in?
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Which phase does a cell spend most
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Cytokinesis
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What phase is this cell in?
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What phase is this cell in?
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What phase is this cell in?
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What phase is this cell in?
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What phase is this cell in?
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When do 2 daughter cells split
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47%