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Cell Growth and Division
Division or reproduction is a way of
passing on the genetic code or DNA of
a species from parent to offspring.
Cell Reproduction
Why do cells divide?
• Growth-increase in body size.
• Cell renewal and replacement,
Ex: cuts are healed, red blood cells
replaced.
• New individual (clone) asexual
reproduction
Types of Cell Division
Mitosis• Growth of an organism
• creation of a genetically identical offspring
(Asexual)
• Meiosis- A new genetically different individual is
created (sexual)
The Cell Cycle (Eukaryotic)
Cell Cycle
Series of events the cell goes through as it grows,
Replicates DNA and divides to produce two
identical cells (daughter cells)
•
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Four main stages
Gap 1
Synthesis
Gap 2
Mitosis
Interphase (Gap 1, synthesis, Gap 2)
Three phases cell spends most of its time in
First growth phase G1
- Cell growth and normal function, organelles
increase in number.
- Cell spends most of its time in this phase, varies
for different cells
- Divide if ready and given a signal to (checkpoint)
Synthesis phase S
- DNA is copied, (chromosome replication) forms a
chromatid which is two chromosomes joined by
the centromere
Second growth phase G2
- Normal function
- Preparation for the nucleus to divide (checkpoint)
- Organelles such as microtubes are formed which
are needed for division
Mitosis (M)
Mitosis
- Division of the Nucleus
- Nuclear envelope dissolves
Cytokinesis
- Division of the cytoplasm
- Formation of two new genetically identical
daughter cells
Cells divide at different rates
Q. Which divide faster prokaryotic or
eukaryotic cells?
• Rate is linked to need, Ex an embryo’s cell
division rate is faster than an adult
• G1 varies the most
Q. Why does the lining of your stomach get
replaced every few days?
• G0 unlikely for a cell to divide Ex neurons, white
blood cells
Q. Do you think a skin cell would have a long
or short G1 stage?
Limits to Cell Growth
Question: Is the growth of an organism due
to the size of its cells or the number of
cells?
Number
• 25 million cell divisions a second in the
human body.
Question: Cells grow until they reach a
certain size then divide, why?
Answer: Cell size is limited pg 136
• Surface area to volume ratio of a cell is
important
• The volume can not get to large as the surface
area of the cell will not be able to sustain the
cells needs.
Q. Look at the table: which cell has the greatest
surface area? Which cell has the greatest
surface area to volume ratio?
• Exchange of materials
• If cell is too large not enough substances can
enter and leave the cell to meet its needs
• What is the volume/contents of the
cell?
• Cytoplasm and all its organelles
• What is the surface area of the cell?
• Cell membrane
• What are the needs of the cell?
• Water, oxygen, glucose, wastes
Vocabulary
• Chromosome: condensed DNA and proteins
• Histones: proteins DNA wraps around
• Chromatin: loose combination of DNA and
proteins
• Chromatid: one duplicate chromosome
• Sister Chromatid: two duplicate chromosomes
• Centromere: joins sister chromadids together
• Telomere: ends of chromosomes that do not
carry genes
Regulation of the Cell Cycle
External Regulators
• Respond to signals from outside the cell, from
other near by cells or hormones from other parts
of the body
• Physical: cell to cell contact
• Growth factors: many different proteins that
stimulate cell growth in different cells
• Hormones: Human growth hormone from the
anterior pituitary gland stimulates cell division in
bone cells
Internal Regulators
• Respond to what is going on inside the cell
• Ex: proteins known as cyclins (activate kinases)
and kinases (enzyme controls cell cycle)
• Makes sure all phase are completed before cell
moves on to the next phase these are known as
checkpoints
Apoptosis: programmed cell death
Cancer: uncontrolled cell division
• Cells lose the ability to control their growth (cell
cycle)
• Do not respond to signals from the cell
- Many of them have damaged genes p53 which
help with stopping cell growth or oncogenes
(accelerate growth)
- Damage surrounding tissues
Tumor: disorganized clump of cancer cells which do
not perform the functions of the normal cells
around them
Benign: usually a harmless clump that can be
removed
Malignant: Cancer cells break away and go to other
parts of the body (metastasize)
Causes (Vary)
Known as Carcinogens
- Smoking and air pollutants, Ex lung cancer
- Virus, Ex cervical cancer
- Exposure to radiation and other harmful
chemicals, Ex skin cancer UV light
- Inherited: Some types of breast cancer