Chapter 3: Cell Division
3.1 Cell division occurs in all organisms
3.2 Cell division is part of the cell cycle
3.3 Both sexual and asexual reproduction involve
cell division
Before, you learned:
Cells come from other cells
Cells take in and release
energy and materials
In a multicellular organism,
some cells specialize
Now, you will learn:
How genetic material is organized in
cells
About the functions of cell division
in multicellular organisms
Cell division
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Occurs in all organisms, but performs
different functions:
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Unicellular organisms reproduce through cell
division
Multicellular organisms division is involved in:
Growth, development, repair
 While cells themselves grow, organisms grow
through cells dividing and producing new cells
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http://www.cancerquest.org/cancer-celldivision
Cell division occurs in all organisms
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Tissue culture is a method of biological research in which small
samples of plant or animal tissues are transferred to a flask or
dish in which they can continue to survive. Human tissue cultures
are often grown as single layers of cells in a glass or plastic dish.
Normal cells grow until a single layer of cells just touching each
other covers the surface. When this occurs, cell division stops, a
phenomenon known as contact inhibition.
Cancer cells, however, do not display contact inhibition. After a
single layer of cells is formed, cancer cells continue to divide,
piling into mounds. One strain of cancer cells known as HeLa
cells has been continuously cultured since its isolation in 1951
from Henrietta Lacks, a patient who died of cervical cancer.
Unlike normal cells, which eventually die, many cancer cells
continue to divide.
animation
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1.In the human body, a group of cancer cells can form a mass of
abnormal cells called a tumor. How is the loss of contact
inhibition related to tumor formation
2.How are HeLa cells different from normal cells?
3.Scientists often use tissue culture to test new drugs or to
examine the effects of suspected cancer-causing chemicals. List
possible advantages and disadvantages of using cultured cells
instead of using humans.
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1.The lack of contact inhibition in cancer cells enables these cells to
continue to divide, which can result in the formation of a tumor.
2.HeLa cells are cancer cells that will continue to divide. Normal cells will
eventually stop dividing and die.
3.A possible advantage is that tissue culture can enable scientists to test
new drugs or possible cancer-causing chemicals without the risk of causing
injury or death to humans. Also, tissue culture probably costs less and is
faster. A possible disadvantage might be that the use of tissue culture
testing cannot reveal possible side effects within the body, nor can it
examine how the rest of the human body would respond to the drug or
chemical being tested.
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Genetic Material of a Cell
Contains information for cell
growth
Most contained in
Deoxyribonucleic acid: DNA –
a chemical
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Contains info for growth and
functions
Double helix: two strands of
molecules
DNA
• Everything the cells do is coded
somehow in DNA
• which cells should grow and when
• which cells should die and when
• which cells should make hair and
what color it should be
• Our DNA is inherited from our parents
• We resemble our parents simply
because our bodies were formed
using DNA to guide the process the DNA we inherited from them.
Chromosomes
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DNA typically exists as a
mass of loose strands
DNA is duplicated
(copied)
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Becomes wrapped around
proteins
Compacted into
chromosomes
Chromosomes consist of
two identical structures:
chromatids: held together
at center by centromere
Chromosomes
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Species specific:
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Pattern and number of chromosomes formed
is the same everytime a cell divides
Humans: 46 chromosomes
Fruit flies: 8; Corn: 20
Relationship of DNA and chromosomes?
Chromosomes
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Answer:
Chromosomes consist
of compacted DNA
1. The four letters
All genetic code is spelled out with just four
chemical letters, or bases: adenine (A),
thymine (T), cytosine (C) and guanine (G).
These pair up, A with T and C with G. The
human genome has between 2.8 and 3.5
billion base pairs.
2. DNA double helix
The base pairs form the rungs of the
3. Genes
ladder-like DNA double helix. Running up
and down the ladder are the long
As little as 3% of the total genome is sequences of bases which are the code
made of genes - the rest is
for life. Each cell in the human body
meaningless "junk". Genes are
contains two metres (six feet) of DNA.
special sequences of hundreds or
thousands of base pairs that provide
the templates for all the proteins
which the body needs to produce.
6. Body
5. Nucleus and Cell
The 46 chromosomes are held in the
nucleus found in most cells in the
human body. Nearly every cell in the
body contains the full DNA code for
producing a human.
4. Chromosomes
The total number of genes is not known
- estimates range from 30,000 to
120,000. However many there are, they,
and all the junk DNA, are wrapped up
into bundles called chromosomes. Every
human has 23 pairs of chromosomes,
one set from each parent.
Each of the cells becomes
specialised by obeying just some of
the instructions in the DNA. Blood,
muscle, bone, organs and so on
result. The body is built from 100
trillion of these cells.
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1. The four letters
(A-T, C-G)
2. DNA double helix
3. Genes
4. Chromosomes
5. Nucleus and Cell
6. Body
Summary of DNA
(from book)
1.
2.
3.
4.
5.
DNA is the genetic material of a cell
The DNA wraps around proteins
A chromosome consists of two chromatids held together
by a centromere
Before a cell divides, the DNA becomes compacted into
chromatids
The nucleus is where DNA in all its forms is located
Cell Division in Multicellular Organisms
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Essential for?
Growth, development, repair
A single cell becomes?
Two cells
Damaged cells replaced by healthy cells
Cell Division
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Growth
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Individual cells grow, but this is limited
Due to surface to volume ratio (chapter 2)
 As the cell grows, more processes are needed to
function – demand for instructions from DNA
increase, but amount of DNA remains constant
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Number of cells increase through division
Development
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Cell division AND specialization
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Same genetic material
Cell Division
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Repair
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Cut skin? Skin cells make new cells to heal the
wound
Cells age and die
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Some quicker than others
Lose ~40,000 skin cells per minute!
 Brain cells live a long time
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