Cells need to divide for both unicellular and multicellular organisms. Unicellular organisms like bacteria divide through binary fission to reproduce, while multicellular organisms use cell division to grow, repair damaged cells, and regenerate tissues. There are three main types of cell division: binary fission in prokaryotes, mitosis in eukaryotes which duplicates the cell's DNA and divides the nucleus and cytoplasm, and meiosis which forms sex cells like eggs and sperm. The cell cycle is the series of events that takes a cell from its formation from another cell until its own division into two new daughter cells. It involves an interphase of growth, DNA replication, and cell preparation followed by mitosis

2. Why Do Cells Need To Divide?
 It depends on the organism
 Unicellular organisms like bacteria
(prokaryotes) divide to reproduce
 Multicellular organisms (most eukaryotes)
use it to grow larger and repair damaged
cells.

3. 3 Types of Cell Division
 1. Binary fission-cell division in
prokaryotes
 2. Cell Cycle (with Mitosis)-cell division in
eukaryotes
 3. Meiosis—cell division to form sex cells
(egg and sperm)

4. Prokaryotes
 Divide by binary fission
 Circular DNA
 Results in two cells
genetically the same
 What has to take place
before the cells divide?

5. Eukaryotes
 The Cell Cycle
– Growth
– Repair or replacement of cells.
 Some cells die quickly and need to be
replaced a lot (skin cells).
 Some cells never get replaced (nerve
cells).
 Some organisms can regenerate whole
body parts.

6.  Each cell goes through a
series of phases throughout
its life.
 The cell cycle-all events
between one cell division and
the next
 **ONE REPLICATION & ONE
DIVISION
 2 basic steps: Interphase
(G1, S, G2) and Mitosis (M)
 Result? 2 daughter cells
genetically exact to the
parent cell they came from.

7.  First stage in Interphase
 G=gap
 Newly formed cell will go through intense
growth. Takes in lots of food and energy.
 DNA at this point is unwound and called
chromatin
Interphase

8.  Second stage in Interphase
 S=Synthesis phase.
 All DNA gets replicated during this
phase cell has double the genetic
material (92 chromosomes)

9.  Third stage in Interphase
 G=gap
 Cell grows some more.
 Extra organelles are being made.

10.  After Interphase (G1, S, and G2)
 M=Mitosis
 Mitosis = Nuclear division.
 MITOSIS IS THE DIVISION OF THE
NUCLEUS DURING THE CELL CYCLE!!!
 There are four mitotic steps:
– Prophase
– Metaphase
– Anaphase
– Telophase.

11. Prophase
 Nuclear envelope
will disappear.
 Spindle fiber
forms.

12. Metaphase
 Chromosomes
begin to line up
at the equator of
the cell.
 Spindle fibers
attach to the
center of each
sister chromatid
of the
chromosome.

13. Anaphase
 Spindle fibers
begin to pull
apart sister
chromatids.
Each is now a
chromosome
 Spindle breaks
down after
this.

14. Telophase
 Each side now
has a full set of
chromosomes.
 Nuclear envelope
will reform.

15. Cytokinesis
 “Cytokinesis”—division of
cytoplasm (cleaving the
cell in half.)
 Animal cells form a
“furrow.”
 Plant cells form a new cell
wall.
 Formation of two,
identical daughter cells
with 46 chromosomes
 At first new cells are
smaller than the originals.

16. Overall Cell Cycle Process
 Interphase (G1, S, G2) and Mitosis (Prophase,
Metaphase, Anaphase, Telophase)  IPMAT

17. REGULATION OF CELL CYCLE
 Cell division controlled by
certain proteins called
cyclins
 Cancer cells don’t respond
to the cyclin signals---
uncontrolled growth
(tumors)
 Benign tumors stay intact
 Malignant tumors spread
throughout body
(metastasize)