Module 2 - 2.1.1

• Types of microscopes


  • Light microscope
  • Scanning electron microscope
  • Transmission electron microscope
  • Laser scanning confocal microscope
• Magnification


  The ratio of image size to object size (size of image/size of object)
• Resolution


  The ability to distinguish between two objects that are close together — the ability to provide detail in the image
• Light microscope


  • Magnification of 1000-2000x
  • Resolution of 50-200 nm
  • Used for viewing cells and tissues
• Scanning electron microscope


  • Magnification of 50,000-500,000x
  • Resolution of 0.4-20 nm
  • Used for viewing the surface of cells and organelles, and providing depth in three dimensional images
• Transmission electron microscope


  • Magnification of 300,000-1,000,000x
  • Resolution of 0.05-1.0 nm
  • Used for detailing organelle ultrastructure
• Scanning electron and transmission electron microscopes have better resolution than a light microscope, which means it is worth magnifying the image more as the image will show more detail
• Scanning electron microscope


  • Gives 3D images with depth of field
  • Good for viewing surfaces
• Electron microscopes are large and very expensive. They require trained operatives
• The sample must be dried out and is therefore dead. This may affect the shape of the features seen (called an artefact)
• The image is in black and white, but colours may be added later by computer graphics. These are called false colour electron micrographs
• Laser scanning confocal microscope

  • Magnification of 1000-2000x
  • Resolution of 50-200 nm
  • Used to produce three dimensional images with good depth selection
• Laser scanning confocal microscope can also see living things and have the advantage that they can focus at a specific depth so the image is not confused by other components that are not in focus
• Laser scanning confocal microscope relies on a computer to piece together all the information from the dots of light created by the lasers. This means that the image is an interpretation rather than a real-life image
• Staining


  The application of coloured stains to the tissue or cells
• Purpose of staining


  • Makes objects visible in light microscopes
  • Increases contrast so that the object can be seen more clearly
  • Is often specific to certain tissues or organelles
• Specific stains


  • Acetic orcein stains chromosomes dark red
  • Eosin stains cytoplasm
  • Sudan red stains lipids
  • Iodine in potassium iodide solution stains the cellulose in plant cell walls yellow and starch granules blue/black
• Electron microscope stains


  Heavy metals or similar atoms that reflect or absorb the electrons
• Cells


  The basic unit of living organisms
• Eukaryotic cells


  • Share a similar basic structure containing membrane-bound organelles
  • Each organelle, whether membrane-bound or not, has its own function within the cell
• Preparing cells and tissues to view under a light microscope

  1. Create a smear

  2. Cut a very thin section

  3. Stain appropriately

  4. Cover by a cover slip
• Viewing these cells, interpreting what you can see and drawing what you see are important skills
• Ultrastructure


  The detail you can see using an electron microscope
• Cell


  • Organelles work together to achieve the overall function
  • Many organelles involved in production and secretion of proteins
• Protein production and secretion

  1. mRNA leaves nucleus via nuclear pores

  2. Ribosomes on rough ER construct protein

  3. Protein travels in vesicle to Golgi apparatus

  4. Golgi apparatus modifies and repackages protein

  5. Vesicle moves to cell surface membrane

  6. Vesicle fuses with membrane to release protein
• Cell types


  • Prokaryote
  • Eukaryote