Announcements: ● TA exam practice session tomorrow 6-7pm Morrill 319 Chapter 2 - Microbial Cell Structure and Function 2.1 Some Principles of Light Microscopy ● Compound light microscope uses visible light to illuminate cells ● Many different types of light microscopy: ○ Bright-field ○ Phase-contrast ○ Dark-field ○ Fluorescence ● Two sets of lenses from the image ○ Objective lens and ocular lens ○ Total magnification = objective magnification x ocular magnification ○ Maximum magnification is ~2000x iClicker 1) If the magnification of an ocular lens of a microscope is 10x and the magnification of the objective on the same microscope is 47x , the total magnification is A) 470 iClicker 2) Function of objective lens A) Gives the main ● Magnification:  the ability to make an object larger ● Resolution : the ability to distinguish two adjacent objects as separate and distinct ○ Resolution is determined by the wavelength of light used an numerical aperture of lens ○ Limit of resolution for light microscope is about .2 um iClicker 1) the ultimate limit of what we are able to see with a microscope is dictated by a) Resolution Improving Contrast in Light Microscopy ● Differential stains separate bacteria into groups ● The gram stain is widely used in microbiology ● Bacteria can be divided into two major groups ○ Gram positive (G+)■ Purple → stay purple ○ Gram negative (G-) ■ Colorless → pink to red iClicker 5) a differential stain is called “differential” because it does not stain all kinds of cells the same color A) TRUE Improving Contrast in Light Microscopy ● Fluorescence Microscopy ○ Used to visualize specimens that fluoresce ■ Emit light of one color when illuminated with another color of light (cyanobacteria) ○ Cells fluoresce naturally (autofluorescence) or after they have been stained with a fluorescent dye like DAPI ■ DAPI is molecule which can bind to DNA ○ Widely used in microbial ecology for enumerating bacteria in natural samples Nobel Prize 2008 ● Awarded jointly for discovery and development of the green fluorescent protein, GFP ● You can attach protein to another protein → express it in bacteria, humans etc. ● GFP → Electron Microscopy ● Use electrons instead of photons to image cells and structures - short wavelengths, higher resolution ● Two Types ○ Transmission Electron Microscopes (TEM) ■ Protein complex ■ DNA ■ Cytoplasm ○ Scanning Electron Microscopes (SEM) Cell Morphology ● Cell shape ● Major cell morphologies ○ Coccus - spherical or ovoid ○ Rod - cylindrical shape ○ Spirillum - spiral shape● Cells with unusual shapes ○ Spirochetes - appendaged bacteria, and filamentous bacteria ● Many variations on basic morphological types ● Larger objects take longer time to exchange heat to reach the center of the object iClicker 6) Compared to eukaryotes, bacteria and archaea generally have ____ surface-to-volume ratios causing _____ nutrient exchange and growth rates a) Higher / higher b) Small volume - higher surface- volume ratio 2.7 Membrane Structure ● Composition ○ Fatty acids point inwards to form hydrophobic environment; hydrophilic portion remain exposed to external environment or the cytoplasm   ● Cytoplasmic membrane ○ 8-10 nm wide ○ Embedded proteins ○ Stabilized by hydrogen bonds and hydrophobic interactions ○ Somewhat fluid iClicker 7) a hydrophilic and charged molecule can readily diffuse through cytoplasmic membrane A) Charged molecules don’t pass through membrane Peptidoglycan ● Gram-positive cells○ Can contain up to 90% peptidoglycan ○ Common to have teichoic acids (acidic substanced) embedded in their cell wall ■ Lipoteichoic acids: ● teichoic acids - covalently bound to