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Cell Observation Techniques: A Microscopic Tour Through History

Explore the evolution of cell observation techniques, from the invention of the compound microscope to modern electron microscopes. Discover how these tools reveal the intricate structures within cells, leading to groundbreaking discoveries in cell biology. Learn about the importance of using various microscopy methods to gain a comprehensive understanding of cell organization and function. Delve into the history of cell studies and the key scientists who contributed to the cell theory. Unveil the differences between prokaryotic and eukaryotic cells and understand the significance of cell size and organization.

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Cell Observation Techniques: A Microscopic Tour Through History

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  1. Chapter 6: A Tour of the Cell

  2. Observation • Is the keystone of science. • Need: Techniques to observe cells.

  3. Question ? • Can cells be seen with the naked eye? • Yes, a few are large enough, but most require the use of a microscope.

  4. Microscope History • 1590 - Janseen Brothers invent the compound microscope. • 1665 - Robert Hooke “discovers” cells in cork. • Early 1700’s - von Leeuwenhoek makes many observations of cells including bacteria.

  5. Light Microscope - LM • Uses visible light to illuminate the object. • Relatively inexpensive type of microscope. • Can examine live or dead objects.

  6. Light Microscope Occular Lens Objective Lens Stage with specimen Light Source

  7. Magnification • Increase in diameter or size.

  8. Resolution • Ability to detect two discrete points as separate from each other. • As Magnification increases, resolution decreases. • LM working limits are 100 - 1000X.

  9. Limitations - LM • Miss many cell structures that are beyond the magnification of the light microscope. • Need other ways to make the observations.

  10. Light Microscope Variations • Fluorescence: uses dyes to make parts of cells “glow”. • Phase-contrast: enhances contrasts in density. • Confocal: uses lasers and special optics to focus only narrow slides of cells.

  11. Electron Microscopes • Use beams of electrons instead of light. • Invented in 1939, but not used much until after WWII.

  12. TEM SEM

  13. Advantages • Much higher magnifications. • Magnifications of 50,000X or higher are possible. • Can get down to atomic level in some cases.

  14. Disadvantages • Need a Vacuum. • Specimen must stop the electrons. • High cost of equipment. • Specimen preparation.

  15. Transmission Electron Microscope - TEM • Sends electrons through thinly sliced and stained specimens. • Gives high magnification of interior views. Many cells structures are now visible.

  16. TEM Limitations • Specimen dead. • Specimen preparation uses extreme chemicals so artifacts are always a concern.

  17. Scanning Electron Microscope - SEM • Excellent views of surfaces. • Produces 3-D views. • Live specimens possible.

  18. Limitations • Lower magnifications than the TEM.

  19. EM Variations • High Voltage TEM • Tunnel SEM • Elemental Composition SEM

  20. TEM - interior SEM - surface

  21. Cell Biology or Cytology • Cyto = cell - ology = study of • Should use observations from several types of microscopes to make a total picture of how a cell is put together.

  22. Other Tools for Cytology • Cell Fractionation • Chromatography • Electrophoresis

  23. Cell Fractionation • Disrupt cells. • Separate parts by centrifugation at different speeds. • Result - pure samples of cell structures for study.

  24. Cell Fractionation

  25. Chromatography • Technique for separating mixtures of chemicals. • Separates chemicals by size or degree of attraction to the materials in the medium. • Ex - paper, gas, column, thin-layer

  26. Electrophoresis • Separates mixtures of chemicals by their movement in an electrical field. • Used for proteins and DNA.

  27. History of Cells • Robert Hooke - Observed cells in cork. • Coined the term "cells” in 1665.

  28. History of Cells • 1833 - Robert Brown, discovered the nucleus. • 1838 - M.J. Schleiden, all plants are made of cells. • 1839 - T. Schwann, all animals are made of cells. • 1840 - J.E. Purkinje, coined the term “protoplasm”.

  29. Cell Theory • All living matter is composed of one or more cells. • The cell is the structural and functional unit of life.

  30. R. Virchow • “Omnis cellula e cellula” • All cells are from other cells.

  31. Types of Cells • Prokaryotic - lack a nucleus and other membrane bounded structures. • Eukaryotic - have a nucleus and other membrane bounded structures.

  32. Prokaryotic Eukaryotic Nucleus

  33. Eukaryotic Prokaryotic

  34. How small can a cell be? • Mycoplasmas - bacteria that are .1 to 1.0 mm. (1/10 the size of regular bacteria).

  35. Why Are Cells So Small? • Cell volume to surface area ratios favor small size. • Nucleus to cytoplasm consideration (control). • Metabolic requirements.

  36. Basic Cell Organization • Membrane • Nucleus • Cytoplasm • Organelles

  37. AnimalCell

  38. Plant Cell

  39. Membrane • Separates the cell from the environment. • Boundary layer for regulating the movement of materials in/out of a cell.

  40. Cytoplasm • Cell substance between the cell membrane and the nucleus. • The “fluid” part of a cell. Exists in two forms: • gel - thick • sol - fluid

  41. Organelle • Term means "small organ” Formed body in a cell with a specialized function. • Important in organizational structure of cells.

  42. Organelles - function • Way to form compartments in cells to separate chemical reactions. • Keeps various enzymes separated in space.

  43. Nucleus • Most conspicuous organelle. • usually spherical, but can be lobed or irregular in shape.

  44. Structure • Nuclear membrane • Nuclear pores • Nucleolus • Chromatin

  45. Nuclear Membrane • Double membrane separated by a 20-40 nm space. • Inner membrane supported by a protein matrix which gives the shape to the nucleus.

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