Transcript Chapter 10, 10.4 & 30.1

Cell Growth and
Division
Chapter 10(M)
Limits to Cell Size
Cells grow and increase in size
 Upper limit to the size of a single cell
 If cells keep growing

 More
demands are placed on the DNA
 Cells becomes less efficient in moving
nutrients and wastes

Cells divide before it becomes too large
Cell Size

As a cell increases in size its volume increases
faster than its surface area.
 Smaller
objects have a greater
ratio of surface area to volume.
Purpose of Cell Division
Cell division  essential for life

1.
Repair replacement of lost or
damaged cells
Skin cells are constantly being replaced
2.
3.
Growth cells divide and increase in
size, so that organism can grow
To maintain a favorable Surface
area to volume ratio
Infant Baby Child Adult
Cell Division and Reproduction
 Asexual
Reproduction
 Sexual Reproduction
Asexual Reproduction
Production of offspring from a single
parent
Offspring is identical to parent
Ex bacteria, yeast, unicellular organisms
& some multicellular organisms

Binary Fission Bacteria
Budding Yeast
Sexual Reproduction
Two parents are involved
 Genetic material from each parent
combines
 Offspring is different from parent

The Process of Cell Division

Genetic material - packaged as DNA is
distributed to two daughter cells
DNA
mitotic chromosome
chromatin
Chromosomes and Cell Division
1.
2.
3.
Chromatin fibers of DNA and
protein
Chromosomes Chromatin fibers
condense and become visible compact
structures
Sister Chromatids before the cell
divides the DNA duplicates and forms
identical copies
Prokaryotes and Eukaryotes
Prokaryotes, the genome is often a
single long DNA molecule
 Eukaryotes, the genome consists of
several DNA molecules
 DNA is passed from one generation to
the next

The Cell Cycle
An orderly sequence of events that
extends from the birth of a cell till the
time it divides itself
 All Eukaryotic cells undergo this cycle
 Cycle is divided into

 Interphase
 Mitotic
Phase
The Cell Cycle
Interphase 90% of the Cell Cycle
1.
G1(gap)phase: cell
spends most of its
functional life.
Gap bet. DNA syn
& cell div
 Cell grows, protein
& organelles
synthesized

Interphase 90% of the Cell Cycle
1.
G1(gap)phase: cell
spends most of its
functional life.
Gap bet. DNA syn
& cell div
 Cell grows, protein
& organelles
synthesized

Interphase contd.

S-Phase the DNA
synthesis phase.
 DNA
molecules are
copied or replicated,
single stranded DNA
in G1 phase to double
stranded DNA in G2.

G2 Phase
completion of DNA
syn. & onset of cell
division
Mitotic Phase
Division of the nucleus
plus cytokinesis, 
produces two identical
daughter cells
 Interphase is not part
of mitosis, it
encompasses stages
G1, S, and G2 of the
cell cycle.

Interphase
 Chromatin
not visible
 DNA replicated
 New organelles are formed
 Cell grows by producing
proteins and cytoplasmic
organelles
 Prepares for cell division.
Mitosis
 Division
of the Nucleus
 Stages
Prophase
Metaphase
Anaphase
Telophase
Prophase





Chromosomes condensed
and visible with sister
chromatids joined
together
The nucleoli disappear
Centrioles at opposite
poles of cell
The mitotic spindle
begins
to form
Phase ends with the
breakdown of the
nuclear membrane
Metaphase
The second stage
 Chromosomes
gather in the a
plate across the
middle of the cell
 Mitotic spindle is
fully formed
 All chromosomes
are attached to
the spindle
microtubules

Anaphase




The third stage of
mitosis
The sister
chromatids suddenly
separate from their
partners.
Each chromatid 
daughter
chromosomes move
toward the poles
Microtubules
shorten, bringing the
chromosomes closer
to the poles.
Telophase





The final stage of mitosis
The chromosomes reach the
poles of the spindle.
The reverse of prophase
spindle disappears, nuclear
envelopes reform, the
chromosomes uncoil and
lengthen, and nucleoli
reappear.
Two genetically identical
daughter nuclei are formed
Cytokinesis follows
Cytokinesis
 Division
of the cytoplasm
 Occurs along with telophase
 Two daughter cells separate
 Difference in animal and plant cells
Animal
Cell cell membrane pinches
off to form a cleavage furrow
Plant Cell Cell plate is formed to
divide cell into two
Animal Cell
Plant Cell
Regulating the Cell Cycle

Cell division is affected by
 Cell
Density
 Anchorage
 Regulatory Proteins
Density dependent inhibition


Cultured cells normally
divide until they form a
single layer on the inner
surface of the culture
container
If a gap is created, the
cells will grow to fill
the gap.
Anchorage dependence


Cells must be anchored to a substratum,
typically the extracellular matrix of a tissue.
Cancer cells are free of both densitydependent inhibition and anchorage
dependence.
Regulatory Proteins
Cyclins timing of the cell cycle
 Regulatory proteins

 Internal
 External
 growth factors
 Fluctuates
during cell cycle
Growth Factors

Coordination between cells
 protein
signals released by body cells that
stimulate other cells to divide
Body has many different types
 Each stimulates only cells with that type
of receptor

Apoptosis


Programmed cell death
Apoptotic cells shrink in size, break into
smaller pieces called apoptotic bodies
that other body cells recognize and eat.
What Causes Cancer?
Cells do not have a properly functioning
“cell cycle” control system
 Cells divide excessively and result in an
abnormal mass of cells
 tumor-suppressor genes  gene p53

 inhibits
cell division
 if switched “OFF” can cause cancer
Growth Factors and Cancer

Growth factors can create cancers
 proto-oncogenes
normal growth factor genes that become
oncogenes (cancer-causing) when mutated
 stimulates cell growth
 if switched “ON” can cause cancer
 example: RAS (activates cyclins)

 tumor-suppressor
genes
inhibits cell division
 if switched “OFF” can cause cancer
 example: p53

Tumors and Cancer
 Benign
mass of normal cells
Can
be removed surgically
Always remain at their original site
 Malignant
Mass
of cancer cells
Spread to other tissues by entering
the circulatory system
 Metastasis
beyond site
 spread of cancer cells
Types of Cancer
Carcinoma  external or internal
coverings of the body-skin, intestinal
linings
 Sarcoma bone and muscle
 Leukemia and Lymphoma- blood forming
tissues

Treatment of Cancer
 Surgery
 Radiation
therapy high energy
radiation disrupts cell division
 Chemotherapy drugs that inhibit
cell division
 Side effects:
Radiation
can lead to sterility
Chemotherapy can cause nausea, hair
loss