Cell Cycle and Mitosis
Honors Biology
Why is Cell Division Important?
• Unicellular organisms
–Reproduce by cell division
increasing the population.
100 µm
Figure 12.2 A
(a) Reproduction. An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).

Another Type of Cell Division:
Binary Fission
• Prokaryotes (bacteria)
–Reproduce by a type of
cell division called
binary fission
Why Do Multicellular Organisms Depend
on Cell Division?
–Development & Growth
–Repair (ex: tissue renewal)
–Maintenance
200 µm
(b) Growth and development.
This micrograph shows a
sand dollar embryo shortly
after the fertilized egg divided,
forming two cells (LM).
20 µm
(c) Tissue renewal. These dividing
bone marrow cells (arrow) will
give rise to new blood cells (LM).
Cell Division
(aka Mitosis)
Makes 2 genetically identical
daughter cells from 1 parent
cell
Before cells divide
They duplicate their genetic
material  ensures that each
daughter cell receives an exact
copy of the genetic material, DNA
What is the structure of a chromosome?
• Where in a cell is the genetic material/chromosomes
located?
– Nucleus
• Chromatin is an uncoiled mass of DNA and histone
proteins
– Exists in this form the majority of the time!
• Histones are proteins that help DNA
condense
• As a cell prepares to divide it coils
up/condenses:
– We call this CHROMOSOMES (condensed
DNA)
DNA Molecules
• DNA (in nucleus of eukaryotes)
can be in 2 forms
– Chromatin : DNA is not tightly
packed together (loosely coiled)
• Occurs during interphase
– Chromosomes : tightly packed
together (TIGHTLY coiled)
• Occurs during mitosis (cell
division)
Genes
• Segments of DNA
(that make up the
chromosome) are
called genes
• A gene is a
piece/segment of
DNA that stores
genetic information
What happens to chromosomes during cell
division?
• What needs to be done to a chromosome before it can
divide?
– It must DUPLICATE! (DNA Replication)
– After duplication each chromosome consists of 2 identically joined
copies  Sister Chromatids
– Sister Chromatids are held together by centromeres
Chromatin
Chromatid
Sister
Chromatids
(condensed,
duplicated
chromosome)
Double Chromosome Structure
Kinetochore attaches
to spindle fibers
Sister
Chromosomes
Every eukaryotic species has a
characteristic, unique # of
chromosomes in EACH cell nucleus
Ex: Humans have 46 chromosomes
# of chromosomes does NOT
necessarily equal complexity
The Cell Cycle
• The mitotic phase alternates
with interphase in the cell cycle
– Interphasemitosisinterphasemitosis
What is Mitosis!?
• Mitosis is the process where cells divide to
produce new cells
- Occurs in healing (Ex: if you cut yourself)
• New cells are also produced as you grow
- Ex: Day-to-day life (new skin cells!)
• ALL eukaryotic organisms produce new cells
through mitosis
Cell Cycle
• Consists of 2 broad
stages
– 1. Growing Stage called
Interphase
– 2. Cell Division called
Mitotic Phase (M Phase)
• The majority of the cell
cycle (90%) is spent in
Interphase
Phases of the Cell Cycle
INTERPHASE
G1
S
(DNA synthesis)
G2
Figure 12.5
Interphase can be
divided into subphases
– G1 phase (GAP 1 phase)
• cell grows in size
• varies most in length from cell to cell
– S phase (synthesis phase)
• DNA is copied (DNA replication)
–Single  Double
• Each chromosome is single
• DNA replication occurs
• Chromosomes have doubled  each consisting
of two sister chromatids
– G2 phase (GAP 2 phase)
• More growth and preparation (make
proteins) for mitosis
Mitotic Phase
• After Interphase, Mitotic Phase begins
–Two parts of M Phase:
1) Mitosis (division of the nucleus)
2) Cytokinesis (division of the
cytoplasm)
M Phase
• Mitosis – the nucleus and duplicated
chromosomes divide and create two identical
daughter cells
• Cytokinesis – the process by which the
cytoplasm is divided in two.
– Cytokinesis usually begins before Mitosis is
completed.
Refresher…….
The Cell Cycle:
G1 phase:
S phase:
G2 phase:
M phase:
Growth
DNA replication
Preparation for cell division
Mitosis and Cytokinesis
Remember….
Interphase
Prophase
Metaphase
IPMATC
Anaphase
Telophase
Cytokinesis
I Passed My Accelerated Tough Class
Interphase
chromosome
•
•
•
•
Consists of G1, S, G2
Occurs BEFORE Mitosis begins
During S phase, the cell copies its DNA
Chromosomes appear as threadlike coils
Condensed,
duplicated
chromosome
– Made of Chromatin, a combination of DNA and protein
molecules
• As the cell prepares to divide, its chromatin fibers
condense, becoming the compact structure we call a
chromosome.
• Chromosomes are copied (# doubles)
Interphase
• Each chromosome has now been condensed and
duplicated and consists of 2 sister chromatids
• The region where the two chromatids are joined tightly
together is called the centromere.
Interphase: Animal Cell
Mitosis
• Continuous pathway (Early, Mid, &
Late)
• Consists of 4 phases and cytokinesis
– Prophase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis
Prophase (X’s)
“Pack Together”
First phase of Mitosis:
1. Chromatin becomes tightly coiled = chromosomes
–
DNA “packs” together
2. Spindle Fibers (made by the centrioles) begins to form in
the cytoplasm
3. Nuclear envelope breaks down
Late: Nucleus and nucleolus disappear
Prophase:
Prophase:
2. Centrioles move
1.
DNA supercoils into chromosomes
Metaphase (X’s)
“Meet in the Middle”
Second phase of Mitosis:
• Chromosomes attach to the spindle at the centromeres
• Chromosomes line up in the middle of cell
– Called equatorial or metaphase plate
• Spinder fibers pull and tug chromosomes to line up
Metaphase:
Anaphase (V’s)
“Adios and Away”
Third phase of Mitosis:
1. Spindle pulls apart chromosomes
2. SISTER CHROMATIDS separate at
the the centromere and begin moving
to opposite ends (poles) of the cell
3. Each chromatid is now considered its own
chromosome
Anaphase:
***Remember that each chromatid
has the same DNA so each is now
its own chromosome***
Telophase (V’s)
“Two New Cells”
Fourth phase of Mitosis:
1. Chromosomes reach end of
spindle
2. Spindle breaks down
(disappear)
3. Cleavage furrow begins to form
4. Nuclear membrane begins to
reform
5. 2 daughter nuclei
6. Chromosomes  chromatin
Telophase:
Spindle fall apart
Cleavage furrow
Cytokinesis
“Division of the Cytoplasm”
• Occurs in Late telophase
• In animal cells
– a cleavage furrow forms, which
pinches the cell in two.
• In plant cells
– produce a cell plate at the middle of
the cell
• At the end of cytokinesis, there are
two distinct IDENTICAL daughter
cells.
Cytokinesis
•
1.
2.
3.
Final Phase of Cell Division/M Phase
Cleavage furrow pinches all the way through
Result is two new cells
2 cells then enter  Mitosis begins again!
-
•
G1, S, G2 (Interphase)
PMAT & Cytokinesis
Each new cell at the end of mitosis is
DIPLOID
– has a full set of chromosomes
re 12.9 A
Cytokinesis: A Closer Look
Cleavage furrow
Contractile ring of
microfilaments
100 µm
Daughter cells
(a) Cleavage of an animal cell (SEM)
In animal cells
Cytokinesis
occurs by a
process known
as cleavage,
forming a
cleavage
furrow
In plant cells, during cytokinesis
A cell plate forms
Vesicles
forming
cell plate
Wall of
patent cell
1 µm
Cell plate
New cell wall
Daughter cells
Figure 12.9 B
(b) Cell plate formation in a plant cell (SEM)
G2 OF INTERPHASE
PROMETAPHASE
PROPHASE
Aster
Centrosomes
(with centriole pairs)
Chromatin
(duplicated)
Early mitotic
spindle
Centromere
Fragments
of nuclear
envelope
Kinetochore
Nonkinetochore
microtubules
Nucleolus
Nuclear
envelope
Plasma
membrane
Chromosome, consisting
of two sister chromatids
Kinetochore
microtubule
METAPHASE
ANAPHASE
Metaphase
plate
Spindle
Centrosome at
one spindle pole
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Daughter
chromosomes
Nuclear
envelope
forming
Nucleolus
forming
Cell Cycle and Mitosis Animations
• http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/007
2437316/120073/bio14.swf::Mitosis%20and%20Cytokinesis
• http://www.sumanasinc.com/webcontent/animations/content/mitosis.
html
• http://www.johnkyrk.com/mitosis.html
Programmed Cell Death
(Apoptosis)
• If cell doesn’t “pass” checkpoint, it goes through
apoptosis
• Cell signaling is involved in programmed cell death needed
to maintain healthy tissues/ cell function
Figure
21.17
2
µm
What is Cancer?
Cancer cells
– Disease caused by disruption of the control of cell division
– Uncontrollable cell division
– Can spread cancer cells throughout the body
• METASTASIS
– Cancer “masses” displaces normal tissue
– Immortal cells (if enough nutrients)
Cancer cells usually
continue to divide well
beyond a single layer,
forming a clump of
overlapping cells.
Figure 12.18 B
Loss of Cell Cycle Controls in
Cancer Cells
• Cancer cells
– Do not respond normally to the
body’s control mechanisms
– Form tumors
• TUMOR= mass or group of
abnormal dividing cells
– 2 types:
• Benign
– Mass of normal cells
– Remain at original site
• Malignant
– Mass of cells from reproduction
of cancer cells
Why?
• Don’t need growth factors 
maybe they make their own
growth factors
• Mutations in GENES!!!
–Ex: p53, cyclin or Cdk genes
Cancer Treatment
• Radiation  destroys DNA in cancer
cells (these cells have lost ability to
repair damage)
•
High energy radiation disrupts cell division
• Surgery
• Chemotherapy: Chemotherapeutic drugs
interfere with specific steps in cell cycle
– Also effects normal cells 
– Drugs disrupt cell division
• Anti-mitotic drug freezes spindle fibers
Tumor
Lymph
vessel
Blood
vessel
Glandular
tissue
Cancer cell
1 A tumor grows from a
single cancer cell.
Figure 12.19
2
Cancer cells invade
neighboring tissue.
3 Cancer cells spread
through lymph and
blood vessels to
other parts of the body.
Metastatic
Tumor
4 A small percentage of
cancer cells may survive
and establish a new tumor
in another part of the body.