The Cell Cycle
Cell division is what allows
cells to reproduce so you
grow and heal certain
injuries.
 Each time a cell completes
a cycle, it becomes two
cells.
 The 3 main stages of the
cell cycle are:





1. Interphase – the cell grows and
copies its DNA
2. Mitosis – the cell’s nucleus and
DNA divide
3. Cytokinesis – the cell’s
cytoplasm divides, creating a new
cell.
*can take anywhere from 8 hours to
1 year (averages about 12-24 hrs.)
Interphase







The cell grows and matures
DNA is duplicated and prepares
for division
3 stages:
1. G1 –the cell grows and
carries out normal cell functions
(occurs right after it finished
dividing)
2. S – the cell copies its DNA
3. G2 – the cell continues to
grow and prepares to divide;
DNA condenses and thickens.
Centrioles appear.
TAKE A MINUTE AND DRAW
WHAT IS HAPPENING.
Mitosis


This is the stage
where the DNA is
separated and passed
into two new
genetically identical
daughter cells.
Also used to repair
damaged cells (under
the scab, existing skin
cells created new skin
cells to fill in the gap
caused by the injury)
THE STEPS OF MITOSIS
•
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Remember – PMAT OR Please Make
Another Taco)
Mitosis cont - Prophase





Prophase is the first stage of
mitosis (and where the dividing
cell spends the most time)
Each chromosome condenses,
until it is now a single structure
that contains the genetic
material that was replicated in
interphase (each half of the X is
called a sister chromatid)
Sister chromatids are
structures that contain identical
copies of DNA.
The center of the chromosome
where the sister chromatids are
attached is called a centromere
DRAW AND LABEL WHAT IS
HAPPENING
Mitosis – Prophase cont.
Spindle fibers form in the
cytoplasm, and centrioles
migrate to the ends (poles)
of the cell (these form the
spindle apparatus).
 The nuclear envelope
seems to disappear
 Spindle fibers attach to the
sister chromatids of each
chromosome (on both sides
both sides of the
centromere), then attach to
opposite poles of the cell
(this way each new cell gets
one complete copy of the
DNA)
 DRAW AND LABEL WHAT
IS HAPPENING

Mitosis cont. - Metaphase



2nd phase of mitosis
The sister chromatids
are pulled by motor
proteins along the
spindle fibers toward
the center of the cell
and line up in the
middle (or equator) of
the cell.
DRAW AND LABEL
WHAT IS
HAPPENING
Mitosis cont - Anaphase
3rd stage of mitosis
Chromatids are pulled apart
The walls of the centrioles
(microtubules) begin to
shorten, which pulls at the
centromere of each sister
chromatid, causing them to
separate into 2 identical
chromosomes
 All the sister chromatids
separate simultaneously
(we don’t know how)
 Finally, the chromosomes
move toward the poles of
the cell
 DRAW AND LABEL WHAT
IS HAPPENING



Mitosis cont - Telophase
The last stage
The chromosomes
arrive at the poles and
begin to relax (or
decondense)
 2 new nuclear
membranes begin to
form and the nucleoli
reappear.
 The spindle apparatus
comes apart
 DRAW AND LABEL
WHAT IS
HAPPENING


Cytokinesis – The last step in the
cell cycle (not part of mitosis)




The cytoplasm
divides and pinches
off
Results in two new
cells, each with
identical nuclei
These two cells then
begin Interphase
DRAW AND LABEL
WHAT IS
HAPPENING
Cell Death



Apoptosis –
programmed cell death
(the cells shrink and
shrivel in a controlled
process)
Happens in your hands
and feet as they begin
to develop, or when a
leaf falls from a tree
Necrosis – cell death
due to injury or illness
of the tissue