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Mitosis
The Cell Cycle and Cell Division
Let’s Review
•
All living things are made of tiny cells.
These cells work dividing in order to
replace cells that are old, damaged, or
dead.
•
These new cells allow us to grow, and
they allow scrapes and wounds to heal!
This process of cell growth, replicating and
dividing is called a cell cycle.
The cell cycle of your cells and the cells of all other
living things is divided into two phases: a growth
phase (called Interphase) and a cell division phase
(called Mitosis).
The Life of a Cell
Mitosis
Interphase
Notice that Mitosis is
only a very small
portion of the cell
cycle.
Interphase is divided into three parts:

•
G1:
cells grow and
prepare for DNA
replication

S:
a copy of the cell’s
DNA is made
•

•
G2:
DNA molecules
begin to coil
The Cell Cycle
The DNA coils into
Chromosomes, chromsomes:
Pass GENETIC information from one
generation of cells to the next
 Found in the nucleus of a cell
 Are made of DNA & PROTEINS
 Different cells types have different
NUMBERS of chromosomes
 Are ONLY visible during division

Chromosomes
Consist of 2
identical “sister”
CHROMATIDS
 Attached at the
centromere
 Human body
cells have 46
chromosomes
Sister
chromatid

centromere
The cell division phase has two parts: mitosis and
cytokinesis.

Mitosis is divided into four
phases.

Look at the next few slides
to see what happens in
each of the four phases.
1st Phase
(PACK)
DNA
and proteins
condense (PACK) into
chromosomes
1st Phase: DNA PACKS into Chromosomes
nd
2
Phase (MIDDLE)
Chromosomes line
up across the
center (middle) of
the cell
 Chromosomes
attach to the
spindle fiber at its
centromere

2nd Phase: Chromosomes line up in the MIDDLE of
the cell
rd
3
Phase (APART)
Sister chromatids
separate (move
apart) into
individual
chromosomes
 Spindle fibers pull
the chromosomes
to opposite sides
of the cell

3rd Phase: Chromosomes are pulled APART
to opposite ends of the cell
th
4
Phase: (TWO)
Chromosomes
gather at
opposite ends
of the cell and
lose their shape
 Two new
nuclear
membranes
form

4th Phase: TWO new cells are formed (still attached)
Cytokinesis
Occurs with
Telophase
 The RESULT: Two
new IDENTICAL
cells are formed.

What happens when cells do not divide
or divide too much?....CANCER
- Cells have internal & external regulators
that control cell division
- Cancer cells do not respond to the
regulators so they have uncontrolled cell
growth and form tumors
* benign tumors
* malignant tumors