CELL DIVISION

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CHAPTER 10

• CELL DIVISION

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• How does a single cell and end up as
  multicellular organism?
• In your groups, discuss IN YOUR OWN WORDS, how
  this can possible happen.

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Lets take a look
1 cell
becomes 2 cells
then 4 cells..
then 8 cells..
and 16 cells and so on.
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But how does that one cell become all the
different cells that make up an organism?

• Cell Differentiation
• Cell Specialization

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Stem cells differ from other kinds of cells in
the body. All stem cellsregardless of their
sourcehave three general properties they are
capable of dividing and renewing themselves for
long periods they are unspecialized and they
can give rise to specialized cell types.
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Cell Differentiation

• The process during which young, immature
  (unspecialized) cells take on individual
  characteristics and reach their mature
  (specialized) form and function.

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Cell differentiation
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Cell specialization

• CELL SPECIALIZATION occurs because many forms of
  life have many levels of organization. In most
  plants, animals, and fungi, cells are organized
  into different types of tissues. TISSUES are
  groups of cells that carry out a common function.
  
• Cell Specialization occurs so that only a portion
  of any given cell's genetic potentialities are
  activated. Thus, cells that share the same
  chromosomes begin to serve different functions
  within the developing organism.

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You now know a bit about HOW this happens but
WHY should you care to learn about it ?????
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Some of the reasons include..

• Cancer
• Stem cell research to cure neural diseases,
  disorders and paralysis ( the ethical dilemmas
  that follow)
• Birth defects
• http//www.pbs.org/wgbh/nova/miracle/program.html

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So lets take a look at cell division

• THE BEGINNING OF IT ALL..
• MITOSIS

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CHAPTER 10 Cellular Transport and the Cell Cycle
Review Vocabulary organelle the membrane bound
structures within eukaryotic cells
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10.2 Cell Growth and Reproduction Cell Size
Limitations Why dont paramecium grow to the size
of elephants?
Height3-4 meters Weight4-7 tons
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Typical Cell Sizes - red blood cells 10 um
- nerve cells, large animals 1 m
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- ostrich egg yolk 10 cm - average cell 2
200 um
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What explanation can you give for the variety of
shapes and sizes of cells???
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Here are the 3 main reasons that a cell has size
limitations 1. diffusion 2. DNA 3. surface
area/ volume ratio
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1. diffusion the larger the cell, the slower
the process 2. DNA the larger the cell, the
more proteins needed thus, nucleus cant keep
up 3. surface area/volume ratio as cells size
increases, its volume increases much faster than
its surface area
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Check this out!!! here is a cubic cell that
measures 1mm on each side the total surface area
would be 6mm2 1mm x 1mm x 6 sides 6mm2 and the
volume would be 1mm3 (1x1x1) and a 2mm cubic
cell would have a surface area of 24mm2 and a
volume of 8mm3 Examine the difference carefully
the surface area increased by a factor of ____
but the volume increased by a factor of ____
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- What does this mean for cells??? - How does
the surface area-to-volume ratio affect cell
function?
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ANSWER if a cell size doubles, the cell would
require 8x more nutrients and would have 8x more
waste to remove. The surface area, however, has
only increased by a factor of 4 and the plasma
membrane would not have enough surface area to
maintain the metabolic processes of the cell.
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Cell Reproduction
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CHAPTER 10.2

• Cell Division in Prokaryotes
• Hereditary material is in form of a single long
  circular molecule of DNA
• Replicated before cell division 2 chromosomes
  are attached to different spots on interior of
  cell membrane

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CHAPTER 10.2

• Cell elongates, chromosomes move apart
• Membrane pinches inward, a new cell wall forms

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CHAPTER 10.2

• Cell division in Eukaryotes
• Mitosis replication and division of the genetic
  material
• Cytokinesis process that divides cell into two
  cells

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CHAPTER 10.2

• Cell cycle
• Regular sequences of cell growth and division
• 10 phases

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CHAPTER 10.2

• INTERPHASE
• G1 period of intensive biochemical activity
• Increases in size
• Enzymes, ribosomes, mitochondria increase in
  number
• ER is renewed and enlarged
• Centrioles separate from each other (not present
  in fungi, flowering plants and some round worms)
• Mitochondria and chloroplast replicate own DNA

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CHAPTER 10.2

• INTERPHASE

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CHAPTER 10.2

• S phase
• Synthesis phase
• DNA is replicated

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CHAPTER 10.2

• G2 phase
• Chromosomes in form of chromatin slowly begin to
  coil and condense
• Replication of centriole pair

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Summary -Interphase

• DNA replicates
• Chromosomes in form of chromatin
• Cant see DNA in the nucleus
• Stages are G1, S, G2

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Mitosis actual division of nucleus

• Divided into 4 parts
• Prophase
• Metaphase
• Anaphase
• Telophase

This is after S, the chromosomes (DNA) are in
duplicate
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One duplicated chromosome
Two sister chromatids attached by a centromere
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Prophase

• The chromatin, diffuse in interphase condenses
  into chromosomes
• Each chromosome has duplicated and consists of
  two sister chromatids
• Nuclear envelope breaks down

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PROPHASE CONTINUED

• Nucleolus disappears
• In animal cells, centrioles move to ends of cell
  begin to make spindle and aster fibers
• Plants make spindle fibers without
  centrioles
• Longest phase of mitosis

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Metaphase

• Shortest phase
• Centromeres of doubled chromosomes attach to
  spindle fibers
• Chromosomes line up at the equator

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METAPHASE
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Anaphase

• Centromeres divide
• Sister chromatids separate and move toward the
  poles
• Sister chromatids (once divided) called
  chromosomes
• Ends when movement stops

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Telophase

• Sister chromatids arrive at the poles
• Spindle breaks down
• Chromosomes stretch out into chromatin form
• Nuclear membrane reforms
• Nucleolus appears

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Cytokinesis cytoplasm division

• The cell membrane pinches in producing two
  daughter cells
• Cleavage always occurs at the midline
• Animal cells cleavage furrow
• Plant cells cell plate

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Cytokinesis in plants

• Cell plate (made of cell wall material) forms
  between two new cells

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CHAPTER 10.2

• http//www.cellsalive.com/mitosis.htm

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CHAPTER 10.2

• Cell being magnified
• Chromosomes replicate
• Chromosomes shorten and thicken
• Prophase
• Metaphase
• Anaphase
• Telophase

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CHAPTER 10.3

• CELL SPECIALIZATION
• Specific cells are uniquely suited to carry out
  specific functions

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CHAPTER 10.3

• Macrophage a cell that provides protection
• Neurons carry out communications by nervous
  system impulses
• Tissue group of similar cells that perform
  similar functions

• Organs group of tissues that work together to
  perform a specific function
• Organ system a group of organs that perform
  several closely related functions

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CHAPTER 10.3

• CYCLINS AND CELL CYCLE
• Cells must be regulated there must be phases
  that happen at certain times to avoid chaos
• Cyclin proteins that regulate the timing of
  cell cycle

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CHAPTER 10.3

• ANALOGY
• Each phase of a cell cycle represents a class in
  school
• Cyclin is the bell and tells when it is time to
  change

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CHAPTER 10.3

• CYCLINS
• Are ONLY in eukaryotic cells
• Cyclin is made at a constant rate and gradually
  builds up inside of the cell
• Once cyclin reaches the critical amount it
  triggers the cell to enter mitosis
• Once the cell enters mitosis, it destroys almost
  all of its cyclin

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CHAPTER 10.3

• SO.
• THE TIME IT TAKES FOR A CELL TO MAKE MORE CYCLIN
  DETERMINES HOW FAST THE CELL MOVES THROUGH THE
  CELL CYCLE

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CHAPTER 10.3

• CELL CYCLE AND CANCER
• Cancer cells dont respond to the usual signals
  that keep other cells from growing uncontrollably
• The reason they dont respond is because of a
  defect in the cell regulation
• Many contain a defect in gene called p53
• Normally halts the cell cycle until all
  chromosomes have been properly replicated
• Defective p53 genes cannot stop uncontrolled
  growth

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CHAPTER 10.3

• CONTROL MECHANISM
• Several check-points to be sure that the cell
  cycle is regulated and moving along at the
  correct sequence
• If growth factors necessary to leave G1 and enter
  S phase are not in sufficient amounts cell will
  remain indefinitely in G1 phase