Cell Cycle
and
Mitosis
Chapter 5
Regular Biology
How Big are YOUR Cells?
• Some cells like a
RBC average in size
of 8um in diameter
• Nerve cells can
reach lengths of 1 m
but have small
diameters
• The cell with the
largest diameter is
the yoke of the
ostrich egg
measuring 8 cm
Why are cells limited to size?
• The cells that make up a multi-cellular
organism come in a wide variety of
sizes and shapes
• There are 3 REASONS Cell’s have
limitations
1. Diffusion Limits Cell Size
• Although diffusion is a fast and efficient
process over short distances, it
becomes slow and inefficient as the
distances become larger.
• Because of the slow rate of diffusion,
organisms can’t be just one giant-sized
cell
2. DNA Limits Cell Size
• The cell cannot survive unless there is
enough DNA to support the protein
needs of the cell
• In many large cells, more than one
nucleus is present
• Large amounts of DNA in many nuclei
ensure that cell activities are carried out
quickly and efficiently.
3. Surface Area-to-Volume
Ratio Limits Cell Size
• As a cell’s size increases, its volume
increases much faster than its surface area
• If cell size doubled, the cell would require
eight times more nutrients and would have
eight times more waste to excrete
• The surface area, however, would increase
by a factor of only four
• This problem would cause the cell to
either starve to death or be poisoned
from the buildup of waste products
1 mm
2 mm
4 mm
1 mm
2 mm
4 mm
1 mm
Surface area = 6 mm2
Volume = 1 mm3
2 mm
Surface area = 24 mm2
Volume = 8 mm3
4 mm
Cell Reproduction
• Remember in the Cell Theory states:
1. All cells come from preexisting cells
• Cell division is the process by which
new cells are produced from one cell
• Cell division results in two cells that are
identical to the original, parent cell.
As we go over this…
• Right now…cells in
your body are
growing, dividing,
and dying
• Old are being shed
& replaced, cuts &
bruises are healing.
Discovery of Chromosomes
• Chromosomes structures, which contain DNA
and become darkly colored when stained, are
and are carriers of the genetic material that is
copied and passed from generation to
generation of cells
Parts of the Chromosome
Centromere
Sister
chromatids
• DNA plus proteins is called chromatin.
• One half of a duplicated
chromosome is a
chromatid.
• Sister chromatids are held
together at the
centromere.
• Telomeres protect DNA
and do not include genes.
telomere
centromere
chromatid
telomere
Sister Chromatid
Sister Chromatids
are pieces of
identical DNA that
are crucial in the
process of cell
replication and
division.
Chromatin to Chromosomes
• DNA wraps around proteins (histones) that
condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
Centromere
Sister
chromatids
Chromosome
Supercoil
within
chromosome
Continued
coiling within
supercoil
Histone H1
Nucleosome
DNA
The Cell Cycle
• The Cell Cycle is a
regular pattern of
growth, DNA
replication, and cell
divisions
The Cell Cycle
• The events that
occur during the cell
cycle are a
continuous process
• 2 major Groups
Make the Cell Cycle
1. Interphase
2. Mitosis
Interphase
Interphase
• Not a true phase of mitosis, but
prepares the cell for division
• Interphase, the busiest phase of the cell
cycle, is divided into three parts.
Interphase
DNA synthesis
and replication
Rapid
growth
and
metabolic
activity
Centrioles replicate;
cell prepares for
division
Interphase
• Interphase
prepares the
cell to divide.
• During
interphase,
the DNA is
duplicated.
Parent cell
centrioles
spindle
fibers
nucleus with
DNA-chromatin
Pair of
Centrioles centrosome
During Interphase
• Period of Growth for the cell by protein
synthesis
• G stands for GAP
1. Gap 1 or G1
2. S or Synthesis
3. Gap 2 or G2
• The main stages Interphase
• G1- cell growth and normal
functions
• S- DNA synthesis-copies
DNA
• G2- additional growth
Cells divide at different rates.
• The rate of cell division varies with the
need for those types of cells.
• Some cells are unlikely to divide (G0)-nerve cells.
Interphase: the resting stage
Interphase Video Clip
Mitosis
• Mitosis is the division of the nucleus or
genetic material of a cell.
• Mitosis is followed by the division of the
cytoplasm: Cytokinesis
• Steps of Mitosis
Prophase, Metaphase, Anaphase &
Telophase
Plant More Apple Trees!
Mitosis Clip
• HMH VIDEO:
• http://my.hrw.com/content/hmof/science/high_school_sci/al/gr912/hmd_bio_9780544765870_/dlo/biologyvideoclips/index.html?
vid=18
• http://my.hrw.com/content/hmof/science/high_school_sci/al/gr912/hmd_bio_9780544765870_/dlo/biologyvideoclips/index.html?
vid=19
Prophase
•
•
•
•
•
The longest phase of mitosis
Double Chromosomes appear
Centrioles move to Opposite Poles
Spindle fibers appear
Chromosomes attach to spindle fibers
by the Centromere
• Nuclear membrane & nucleolus break
down
• Nucleus, Nuclear Envelope & Nucleolus
disappear
Prophase
Prophase
Prophase:
The First Stage of Mitosis
PROPHASE VIDEO CLIP
Metaphase
Double chromosomes (paired chromatids)
attach to the spindle fibers by their
Centromere and line up at the equator
(middle of the cell)
Metaphase
Metaphase:
The Second Stage of Mitosis
METAPHASE: VIDEO CLIP
Anaphase
• Chromatids separate at the Centromere
and begin to migrate to opposite poles
• Centromeres lead the way
• Chromatids cluster together when they
reach the poles
Anaphase
Anaphase
Anaphase:
The Third Stage of Mitosis
ANAPHASE: VIDEO CLIP
Telophase
• Chromosomes form Chromatin
• Nuclei forms around chromatin
• Nucleus, Nucleolus, Nuclear Envelope
& Nuclear Membrane re-appear
• Cytoplasm divides
Telophase
Cytokinesis
• Division of the cytoplasm
• Begins in Telophase
• A cleavage furrow forms in animal cells
at the equator
• A cell plate forms in plant cells and will
become the cell wall
• Cytokinesis differs in animal and plant cells.
– In animal cells,
the membrane
pinches closed.
– In plant cells, a
cell plate
forms.
Telophase:
2 New Daughter Cells
Telophase:
The Last Phase of Mitosis
TELOPHASE VIDEO CLIP
REGULATION OF THE CELL
CYCLE
Internal & External Factors
• Both external & internal factors regulate
the cell cycle
• External Factors: come from outside the
cell
• Internal Factors: come from inside the
cell
External Factors
• External factors include physical and
chemical signals.
• Example: cell to cell contact
– Most mammal cells form a single layer in a
culture dish and stop dividing once they touch
other cells.
Internal Factors
• External Factors can trigger internal
factors
• The most important factors are
• 1. Kinases: moves phosphate groups
from one molecule to specific molecules
• 2. Cyclin: controls Kinase
• Occasionally, cells lose control of the
cell cycle
• Apoptosis is programmed cell death.
– a normal feature of healthy organisms
– caused by a cell’s production of selfdestructive enzymes
– occurs in
development
of infants
webbed fingers
Loss of Control
• Cancer is a malignant growth resulting
from uncontrolled cell division
• Cancer cells do not carry out necessary
functions
• Cancer cells come from normal cells
with damage to genes involved in cellcycle regulation.
• Cancer cells form disorganized clumps
called tumors.
– Benign tumors remain clustered and can be
removed.
– Malignant tumors break away (metastasize), and
can form more tumors.
normal cell
cancer cell
bloodstream
Cancer Therapy
• http://my.hrw.com/content/hmof/science
/high_school_sci/al/gr912/hmd_bio_9780544765870_/dlo/biolo
gyvideoclips/index.html?vid=20
Cancer
• Cancer is the leading
cause of death in the
US exceeded by heart
disease
• Can affect any tissue
in the body
• Lung and Breast
Cancer rate among the
highest
Death Rate of Cancer
Most common:
Breast, Lung, Prostate, Colon
& Skin
Liver Cancer
The causes of Cancer
• 1. Inherited errors in specific genes
- Breast cancer
• 2. Exposure to radiation or chemicals
- Skin cancer
• 3. Some carried by viruses
- Cervical cancer
• 4. Environmental factors
- pollution, tobacco
Organisms reproduce by cell division
ASEXUAL REPRODUCTION
Binary fission is similar in
function to mitosis.
• Asexual reproduction is the creation of
offspring from a single parent.
– Binary fission produces two daughter cells
genetically identical to the parent cell.
– Binary fission occurs in
parent cell
prokaryotes.
DNA
duplicates
cell begins
to divide
daughter
cells
Some eukaryotes reproduce
through mitosis.
• Budding forms a new organism from a small
projection growing on the surface of the
parent.
Hydra
bud
Yeast
• Fragmentation is the splitting of the
parent into pieces that each grow into a
new organism.
• Vegetative reproduction
forms a new plant from the
modification of a stem or
underground structure on
the parent plant.