Structure and function

Structure and function - Microbial (prokaryotic) cell...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Microbial (prokaryotic) cell structure and function Chapter 4 (all sections) Microorganisms could not be adequately studied before the field of microscopy developed; therefore, we will discuss microscopy before the structure of prokaryotic cells. Light microscopy Compound light microscope “light” because visible light is used “compound” because more than one lens magnifies Usually oculars and objectives Total magnification is product of ocular mag. and objective mag. Bright-field light microscope Light microscope that allows light to pass directly to eye without being deflected by a filter or plate Cells are seen in contrast to surroundings BUT cells are mostly water and glass is clear Little contrast without staining Staining Because cells have little contrast with their surroundings, it is difficult to view live, unstained cells in brightfield microscopy. Staining is typically used to increase the contrast between cells and their surroundings, but this kills cells and adheres them to slide. This limits the use of brightfield microscopy in viewing live, mobile cells. The first step in staining is making a smear . Cells are dried and “fixed” to slide. They are dead. Two types of stains: -Simple stain -Stains all cells the same -Differential -Distinguish one group from another -Gram stain
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Phase contrast microscopy Light microscope that takes advantage of, and amplifies, slight differences in refractive index between cells and their surroundings Good contrast without staining - live/mobile cells compare figures 4.5 a and b Darkfield microscopy Light reaches specimen from sides only. This light is scattered by specimens and only this scattered light enters objectives. No staining, live/mobile cells Higher resolution than phase contrast Compare figures 4.5a, b, and c. What is the major advantage in using phase contrast or darkfield microscopy over that of brightfield? How does darkfield and phase contrast microscopy differ? Fluorescence microscopy Add fluorescent dyes that bind to DNA Or the microorganism will naturally be fluorescent due to chlorophyll Also uses light, but not “visible” light. Light of a shorter wavelength (in the ultraviolet or near ultraviolet range) is used. See figure 4.6 for examples. Differential Interference Contrast (DIC) Polarized light that is passed through prism and then through specimen Recombined, but not entirely in phase due to differences in refractive index of the specimen Good at viewing nuclei (eukaryotes) or vacuoles No staining, live cells, 3-dimentional view
Background image of page 2
See figure 4.7a for example. Atomic Force Tiny stylus scans specimen Repulsive atomic forces between probe and specimens 3-dimensional No staining, live cells Figure 4.7b Confocal Scanning Laser Laser coupled to light microscope Scans one layer at a time 3-dimensional Computer can reconstruct layers Stained with fluorescent dyes Figure 4.8ab Electron Microscopy Uses electrons and electromagnets instead of light and lenses. Two types:
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 15

Structure and function - Microbial (prokaryotic) cell...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online