Chapter 3: Cell Division

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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
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Cell division

• Occurs in all organisms, but performs different
  functions
• 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-cell-division

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Cell division occurs in all organisms

• 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.

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animation

• 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
• Contains info for growth and functions
• Double helix two strands of molecules

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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.

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Chromosomes

• DNA typically exists as a mass of loose strands
• DNA is duplicated (copied)
• Becomes wrapped around proteins
• Compacted into chromosomes
• Chromosomes consist of two identical structures
  chromatids held together at center by centromere

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Chromosomes

• Species specific
• 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?

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Chromosomes

• Answer Chromosomes consist of compacted DNA

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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 ladder-like DNA double helix.
Running up and down the ladder are the long
sequences of bases which are the code for life.
Each cell in the human body contains two metres
(six feet) of DNA.
3. Genes As little as 3 of the total genome is
made of genes - the rest is meaningless "junk".
Genes are special sequences of hundreds or
thousands of base pairs that provide the
templates for all the proteins which the body
needs to produce.
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6. Body 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.
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.
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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

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Summary of DNA (from book)

1. DNA is the genetic material of a cell
2. The DNA wraps around proteins
3. A chromosome consists of two chromatids held
   together by a centromere
4. Before a cell divides, the DNA becomes compacted
   into chromatids
5. The nucleus is where DNA in all its forms is
   located

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Cell Division in Multicellular Organisms

• Essential for?
• Growth, development, repair
• A single cell becomes?
• Two cells
• Damaged cells replaced by healthy cells

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Cell Division

• Growth
• 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
• Number of cells increase through division
• Development
• Cell division AND specialization
• Same genetic material

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Cell Division

• Repair
• Cut skin? Skin cells make new cells to heal the
  wound
• Cells age and die
• Some quicker than others
• Lose 40,000 skin cells per minute!
• Brain cells live a long time