Chapter%206%20A%20Tour%20of%20the%20Cell

1
Chapter 6A Tour of the Cell
2
All organisms are composed of cells
3
What is a living cell . . .
. . . self-contained, self assembling, self
adjusting, self perpetuating, isothermal mix of
biomolecules, held in a 3-D conformation by weak
non-covalent forces, which extract raw materials
(precursors) and free energy from the surrounding
environment and which shows great efficiency and
economy of metabolic regulation and that
maintains a dynamic steady state far from
equilibrium and which can self-replicate using
the informational molecule DNA.
4
Cell

• A collection of living matter enclosed by a
  barrier that separates the cell from its
  surroundings
• Basic Unit of all forms of life
• Smallest unit that displays the properties of
  life
• Composed of cytoplasm and surrounded by a plasma
  membrane.

5
(No Transcript)
6
CELL THEORY(1838)
Theodor Schwann
Matthias Schleiden

• All life forms are made from one or more cells.
• The cell is the smallest form of life.
• Cells only arise from pre-existing cells.

7
CELL THEORY
Rudolph Virchow (1855)

• Summarized the cell theory with the Latin phrase
  omnis cellula a cellula (all cells arise from
  cells) in 1855.
• Cells are capable of self-reproduction (e.g.
  only from preexisting cells.

8
Plasma Membrane

• The interface boundary for intra and
  extracellular exchange of materials.

9
Cell Size

• 1 mm (frogs egg) - 1 ?m (1/1000th mm.)
• Determined by membrane transfer characteristics.
• As a cell get larger in volume, relative surface
  area (and relative capability for material
  exchange) decreases.
• Cells needing higher exchange rates have evolved
  to develop modifications such as folding,
  microvilli, multiple nucleii, long skinny shape,
  etc.

10
Take Home Lesson

• Surface-area-to volume ratio
• Limits how large an actively metabolizing cells
  can become. Requires that cells be small.

11
Reasons for Small Cell Size

• As linear dimensions of a cell increase, the
  volume increases twice as fast as the surface
  area.
• Nutrients and wastes must enter and leave the
  cell through the plasma membrane.
• The nucleus can only control a certain amount of
  cytoplasm.
• Materials must be able to move quickly and
  efficiently through the cytoplasm.

12
Microscopy

• Magnification
• Making something larger Function of wavelengths
  shorter wavelengths of light or electrons allow
  greater magnification.
• Resolution
• Minimum distance between two objects before they
  are seen as one larger object.

13
Types of Microscopy

• Bright-Field (Compound) Light Microscope
• Use light rays focused by glass lenses.

14
Types of Microscopy

• Dark-field
• Uses angular light reflected off specimen.

15
Types of Microscopy

• Phase-contrast
• Light is out of phase and gives different
  contrast when brought back together.
• Differential-interference
• contrast
• Light is out of phase and combined with other
  light.

16
Types of Microscopy

• Fluorescence
• Uses fluorescent antibodies to reveal protein in
  cells.
• Confocal
• Uses laser beam to focus on shallow plane
  forms series of optical sections.

17
Transmission Electron Microscope (TEM)

• Electrons pass through specimens focused by
  magnets. Used when internal detail is critical

18
Scanning Electron Microscope

• Uses electrons scanned across metal-coated
  specimen. Used when external detail is critical.

19
SEM vs. TEM
20
Microscopy

• Lets view some examples.

21
Use of the light microscope.
Magnification and Field of View.
22
Review

• List the three principals of the cell theory.
• Define the term cell
• Explain the use of and differences between the
  compound light, transmission electron and
  scanning electron microscopes with respect to
  their ability to increase contrast.
• Define resolution and magnification.
• Why is the size of a cell dependent on the
  cell-volume-to-cell-surface ratio.