Observing the Microbial Cell - Lecture Notes | BIOL 2051, Study notes of Biology

Download Observing the Microbial Cell - Lecture Notes | BIOL 2051 and more Study notes Biology in PDF only on Docsity! In library on first floor at reserve desk: MICROBIOLOGY: An Evolving Science 1st edition- call number is RX52 Circulates 2hrs BUILDING USE ONLY Chapter 2: Observing the Microbial Cell Read Section 2.1-2.6 SIZE OF PROKARYOTES  Prokaryotes are generally smaller than eukaryotes  Small size allows nutrients to reach all parts of cell quickly  Prokaryotic cells can be as small as 0.2μm. The smallest eukaryotic cells are 2μm.  Cocci - typically have diameter of 2 µm  Some microbiologists have proposed that bacteria smaller than 0.2 μm exist in nature, cells referred to as nanobacteria.  If one considers the space needed to house all essential molecules of life, it is unlikely they could exist within a volume available in a cell less than 0.1 μm  Prokaryotic cells can have a wide variety of cell morphologies, which are often helpful in identification. Bacterial Shapes 1. Simplest shape is sphere o singular-coccus o plural- cocci o Arrangement:  Coccus- single cells  Diplococcus- 2 cells  Streptococcus- chains of more than 2 cells  Staphylococcus- grapelike cluster of cells  Tetrads- packets of 4 cells 2. Most common shape is rods o Singular- bacillus o Plural- bacilli o Can be very long & thin or short & fat o Occur singly or in chains 3. Spirals: o Rigid spiral-shaped bacteria are called spirilla (singular- spirllum) o Flexible spiral-shaped bacteria are called spirochetes o Vibrio – curved rods Microscopy  Simple microscopes o one lens o magnify 50 – 300X  Compound microscopes o multiple lenses o Much higher magnifications  Ones in 2051 lab magnify 1000x Lens System of Compound Microscopes  Condenser lens o located between light source and specimen o Focuses light rays up through specimen  Objective lens system o Closest to specimen o Typical scope has 10, 40, & 100X objective lenses o In each objective are multiple lenses  Ocular lens system o Closest to the eye o Typically magnify 10x o Each ocular has multiple lenses Magnification  A microscope with a 100X objective and 10X ocular has a total magnification of 1000x  This means an object will appear 1000x larger than it is  Can see bacteria at this magnification, but not internal structures  Cannot see viruses Resolution  ability to distinguish between 2 objects that are close together  Limits the usefulness of a microscope  Highest resolution of a typical light microscope is 0.2 micrometers  This means that 2 objects closer than 0.2 µm to each other can’t be distinguished  Resolution is determined by wavelength of light and numerical aperture  Increasing resolution 1. Multiple lenses - Correct each other’s aberrations 2. Use shorter wavelength light - Blue light (~400nm) is shortest wavelength so gives highest resolution 3. Increase numerical aperture (measure of light gathering ability of objective lens) - Wider lens closer to specimen - Immersion oil - light bends as it passes through specimen into air- reduces resolving power - If space between specimen and objective is replaced with immersion oil, resolution increases - Oil keeps light from scattering as much as in air 4. Increase contrast - Contrast between bacteria & background is small so bacteria are very hard to see - Increase contrast by staining cells or using special type of microscope - Many stains are basic dyes  Chromophore (pigmented portion) has positive (+) charge  Cell surface has negative (-) charge  Examples- crystal violet, methylene blue, safranin