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They grow and divide!
The process of cells growing and dividing is
known as the cell cycle.
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Why do cells need to do this? Hmmm…
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Cell cycle – cells growing and dividing
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There are 3 stages
1. Interphase
2. Mitosis
3. Cytokinesis
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All of the cell cycle occurs in the nucleus!
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We need to understand some parts of the cell
before we begin looking at each step.
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Centrioles
Chromatin
DNA
Chromosomes
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Come in pairs
Look like a macaroni noodle or barreled shape
Found in the cytoplasm
Like to hang out at the north pole of the cell
They are orange here
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Definition: Mass of genetic material
composed of DNA and proteins.
Chromatin is located in the nucleus of a cell.
During mitosis (2nd stage), chromatin
condenses to form chromosomes.
I mentioned that chromatin
is made of DNA.
 What is DNA?
 DNA, or deoxyribonucleic acid, is the
hereditary material in humans and almost all
other organisms.
 Most DNA is located in the cell nucleus.
 So, chromatin is composed of DNA and
chromatin condenses to form chromosomes.
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Once again chromatin
is composed of DNA
and chromatin
condenses to form
chromosomes.
What are
chromosomes?
◦ It is a single piece of
coiled DNA
The centromere acts
like a button. It keeps
the 2 chromatids
together making the
double rod “X”
structure.
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Interphase: Growth Phase
This is the period where the cell grows and
prepares for division. It is divided into three
parts:
◦ G1: The cell grows
◦ S: The cell replicates its chromosomes (DNA).
◦ G2: The cell replicates its organelles and prepares
for division.
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During interphase, the chromosomes are not
visible. They are uncoiled. When the DNA is
in this uncoiled form it’s called chromatin.
The reason it’s uncoiled is this allows it to be
copied more easily.
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The cell spends most of its life in the
interphase stage.
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http://www.phschool.com/atschool/phsciexp
/active_art/cell_cycle/index.html
Now the cell is ready to divide. Next stage…
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Mitosis: Division of the Nucleus
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This is divided into four steps:
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
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Chromatin condenses to form chromosomes
Centrioles move to opposite ends of cell
Nuclear envelope starts to break down.
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http://www.phschool.com/atschool/phsciexp
/active_art/cell_cycle/index.html
Time to move to the next step of mitosis…
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The chromosomes line up in the MIDDLE of
the cell.
The centrioles are at north & south poles.
MMMMetaphase……..MMMMiddle
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http://www.phschool.com/atschool/phsciexp
/active_art/cell_cycle/index.html
Time to move to the next step of mitosis…
Remember the centromeres
that act like a button and hold
the chromosomes together?
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Well, not anymore. The centromeres break.
Thus, the chromosome is seperated and becomes
two chromatids again.
Each chromataid moves
to opposite ends of cell.
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AAAnaphase…AAAway
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http://www.phschool.com/atschool/phsciexp
/active_art/cell_cycle/index.html
Time to move to the last step of mitosis…
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A new nuclear envelope has formed around
each region of chromosomes
TTTwo Nucleus(Nuclei)…TTTelophase
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http://www.phschool.com/atschool/phsciexp
/active_art/cell_cycle/index.html
The last step of mitosis.
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cyto- (cell) and kinesis (motion, movement)
Cytokinesis is the process in which the
cytoplasm of a single eukaryotic cell is
divided to form two daughter cells.
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http://www.phschool.com/atschool/phsciexp
/active_art/cell_cycle/index.html
A look at the last stage of the cell cycle.