Introduction to the Cell

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Introduction to the Cell
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Introduction

• Every living thing-from the tiniest bacterium to
  the largest whale-are made of one or more cells.
• Before the seventeenth century, no one knew that
  cells existed.
• Most cells are too small to be seen with the
  unaided eye.
• Cells were not discovered until after the
  invention of the microscope in the early
  seventeenth century.

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The Microscope

• One of the first microscopes was made by the
  Dutch drapery store owner Anton von Leewenhoek
  (1632-1723).
• With his hand-held microscope, Leewenhoek became
  the first person to observe and describe
  microscopic organisms and living cells.

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• Leeuwenhoek is known to have made over 500
  "microscopes," of which fewer than ten have
  survived to the present day. In basic design,
  probably all of Leeuwenhoek's instruments --
  certainly all the ones that are known -- were
  simply powerful magnifying glasses, not compound
  microscopes of the type used today.

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• In 1665, the English Scientist Robert Hooke
  (1635-1703) used a microscope to examine a thin
  slice of cork and described it as consisting of
  "a great many little boxes".  It was after his
  observation that Hook called what he saw "Cells".
  They looked like "little boxes" and reminded him
  of the small rooms in which monks lived, so he
  called the "Cells".

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The invention of the microscope lead to several
important statements

• In 1838, German Botanist Matthias Schleiden
  studied a variety of PLANTS and concluded that
  all PLANTS "ARE COMPOSED OF CELLS".
• The next year, German Zoologist Theodor Schwann
  reported that ANIMALS are also made of CELLS and
  proposed a cellular basis for all life.
• In 1855- 1858, German Physician Rudolf Virchow
  induced that "THE ANIMAL ARISES ONLY FROM AN
  ANIMAL AND THE PLANT ONLY FROM A PLANT" OR " THAT
  CELLS ONLY COME FROM OTHER CELLS".

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Fundamental Ideas of Cell Theory

1. All living matter is composed of cells.
2. All cells arise from cells.
3. The cell is the basic unit of structure and
   function. (Smallest unit of life.)

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The Cell Theory

• A. Major Contributors.
• Robert Hooke- 1600s
• Anton von Leewenhoek
• Mattias Schleiden 1838 German botanist
• Theodor Schwann 1839 German Zoologist
• Rudolf Virchow 1858

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How Cells are Studied - Microscopy

• 1. Light Compound Microscope

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How the light microscope works

• Most microscopes are called light microscopes
  because they accomplish their task by using
  lenses to bend light rays.

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Observing and Drawing Objects

• Because the light rays from an object cross
  before reaching your eye, the image you see
  through our light microscopes will be inverted
  and upside down.

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Important terms with the microscope

• Magnification the increase of an object's
  apparent size.
• Field of view the area visible through the
  microscope lenses. Field of view decreases as
  magnificaiton increases.
• Resolution the power to show details clearly.
  Resolution allows the viewer to see two objects
  that are very close together as two objects
  rather than as one.

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How Cells are Studied cont

• 2. Scanning Electron Microscope (SEM)
• 3. Transmission Electron (TEM)

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Micrograph a photograph of the view through a
microscope
Light microscope
SEM
TEM
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How Does an Electron Microscope Work?

• Electrons are very tiny negatively-charged
  particles. Because they are negatively-charged,
  they are attracted to anything that is
  positively-charged.
• By applying voltage to a metal plate, we are able
  to make the plate positively-charged so that it
  attracts the electrons.
• Some of the electrons flow through a small hole
  that is in the plate, creating a beam of
  electrons that we aim at our sample with the help
  of magnetic lenses.
• When the electrons hit our sample, the
  interaction is detected and transformed into an
  image.

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Microscopy and Amoeba proteus
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Microscopy and Cheek Cells
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How Cells are Studied (even more!)

• 4. Cell Fractionation and Differential
  Centrifugation

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Cell Fractionation and Differential Centrifugation

• Cell fractionation is the breaking apart of
  cellular components
• Differential centrifugation
• Allows separation of cell parts
• Separated out by size density
• Works like spin cycle of washer
• The faster the machine spins, the smaller the
  parts that settled out

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Cell Structure and Size

• Structure is related to function!
• Cells take the shape that best allows them to
  perform their job.
• Ex. Nerve cells
• Ex. Skin cells
• The ratio of cell surface
  to cell volume
  limits cell size.

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Cell Size

• Most much smaller than one millimeter (mm)
• Some as small as one micrometer (mm)
• Size restricted by Surface/Volume (S/V) ratio
• Surface is membrane, across which cell acquires
  nutrients and expels wastes
• Volume is living cytoplasm, which demands
  nutrients and produces wastes
• As cell grows, volume increases faster than
  surface
• Cells specialized in absorption modified to
  greatly increase surface area per unit volume

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Surface to Volume Ratio
































TotalSurfaceArea (Height?Width?NumberOfSides?Numbe
rOfCubes) 96 cm2 192 cm2 384 cm2
TotalVolume (Height?Width?LengthXNumberOfCubes)
64 cm3 64 cm3 64 cm3 SurfaceAreaPerCube/Volume
PerCube (SurfaceArea/Volume) 1.5/1 3/1 6/1
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Structure and Function
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The Prokaryotic Cell

• Two domains Bacteria and Archaea
• Lacks a nucleus and most other organelles
• DNA concentrated in nucleoid region
• Contains ribosomes, cell wall, and in some cases
  a capsule, pili, and flagella.
• 1-10 micrometers

• Appear earliest in earths fossil record

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Figure 7.4x1 Bacillus polymyxa
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Figure 7.4x2 E. coli
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Prokaryotes

• PROKARYOTES were the only life form for 2 BY!

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Prokaryotic Cells Visual Summary
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Prokaryotic Cells The Envelope

• Cell Envelopes
• Glycocalyx
• Layer of polysaccharides outside cell wall
• May be slimy and easily removed, or
• Well organized and resistant to removal (capsule)
• Cell wall
• Plasma membrane
• Like in eukaryotes
• Form internal pouches (mesosomes)

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Prokaryotic Cells Cytoplasm Appendages

• Cytoplasm
• Semifluid solution
• Bounded by plasma membrane
• Contains inclusion bodies Stored granules of
  various substances
• Appendages
• Flagella Provide motility
• Fimbriae small, bristle-like fibers that sprout
  from the cell surface
• Sex pili rigid tubular structures used to pass
  DNA from cell to cell

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The Eukaryotic Cell

• True nucleus
• Membrane-bounded organelles
• Size 10-100 microns (much
  bigger!)
• Members of Kingdom Animalia, Plantae, Fungi and
  Protista

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Eukaryotic cell

• Nucleus surrounded by its membrane
• Internal organelles bounded by membranes
• 10 100 micrometers
• Domain Eukarya
• Kingdoms Protists, Fungi, Plants, Animals

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Membranes Allow for More Efficient Cellular
Metabolism

• Membranes separate areas to maintain specific
  chemical conditions. (Think about your stomach
  and intestines!)
• This way different chemical processes can take
  place simultaneously.
• Membranes increase the surface area needed for
  many chemical reactions.

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• In other words, the cell can increase in size and
  combine together to form tissues!
• There is no such thing as a multicellular
  prokaryotic organism!
• More on the eukaryotic cell in the next power
  point
• Wait how did membranes and organelles evolve?

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Hypothesized Origin of Eukaryotic Cells
Theory of Endosymbiosis
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Prokaryotes vs. Eukaryotes

• Eukaryotes
• nuclear membrane
• membrane bound organelles (Golgi bodies,
  lysososome, mitochondria, vacuoles, etc.)
• 10-100 microns
• Found in the kindgoms Plantae, Animalia, Fungi,
  Protista

• Prokaryotes
• NO nuclear membrane
• No membrane bound organelles
• contain ribosomes
• 1-10 microns
• Found in the kindgoms Eubacteria,
  Archaebacteria

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Sizes of Living Things
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The size range of cells