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Auburn University
BIOL 3200

VIRUSES, VIROIDS, PRIONS • Viruses contain protein coat surrounding nucleic acid o Essentially protein bag of nucleic acid • Viruses termed obligate intracellular parasites o Must have host machinery to replicate o Inactive outside of host • All forms of life can be infected by viruses • Viruses frequently kill host cells o Some live harmoniously with host MOST IMPROTANT THINGS WE HAVE COVERED • Historical figures and the impact of their ecperiments • Recognize that microbiology has a huge impact on society • Recognize microbiology as an interdisciplinary science • Differientiation between microflora and pathogens • Eukaryotes vs. prokaryotes • Bacteria vs. archaea CHAPTER 2 MOLECULES OF LIFE Macromolecules of the cell DNA and RNA Proteins Lipids General Carbohydrates Chemical bonding in cells Covalent bonds Ionic bonds Hydrogen Bonds CHAPTER 3 MICROSCOPY AND CELL STRUCTURE • Microscopes o Most important tool for studying microorganisms o Use visable light to observe objects o Magnify images approx. 1,000x • Electron microscope (1931) can magnify images in excess of 100,000x • Atomic-force microscope (1981) can view individual atoms • Light microscopy o Light passes through specimen, then through series of magnifying lenses o Most common and easiest to use is the bright-field • Magnification o Microscope has two magnifying lenses  Called compound microscope  Lens include ocular lens and objective lens o Lenses combine to enlarge objects  Magnification iis equal to the factor of the ocular x the objective o Brightfield microscope  Uses light condenser to concentrate light on sample • Resolution o Usefulness of microscope depends on its ability to resolve two objects that are very close together  Resolving power is defined by the minimum distance between two objects • Contrast o Reflects the number of visible shades in a specimen o Higher contrast achieve for microscopy through specimen staining • Examples of light microscopes that increase contrast o Phase-contrast microscope  Amplifies differences between refractive indexes of cells and surrounding medium  Uses set of rings and diaphragms to achieve resolution o Interference microscopy  Causes specimen to appear three dimensional • Depends on subtle differences in refractive index  Most frequently used interference scope is nomarski differential interference contrast o Darkfield microscope  Reverse image • Specimen appears bright on a dark background o Like photographic negative  Achieves image through a modified condenser o Confocal scanning laser microscope  Computer used to reconstruct three dimensional image of thicker structures  Provides detailed sectional views of internal structures of an intact organism • Laser sends beam through sections of organism • Computer constructs 3d image from sections • Electron microscopy o Transmission electron microscope (TEM)  Used to observe fine detail  Directs beam of electrons at specimen • Electrons pass through or scatter at surface o Shows dark and light areas, darker areas more dense  Specimen preparation • Thin section • Freeze fracturing or freeze etching  The specimen preparation can often introduce artifacts • Scanning electron microscope (SEM) o Used to observe surface detail o Beam of electrons scan surface MORPHOLOGY OF PROKARYOTIC CELLS • Prokaryotes exhibit a variety of shaoes o Most common  Coocus • Spherical  Bacillus • Rod or cylinder o Other shapes  Coccobacillus • Short round rod  Vibrio • Curved rod, diagnostic  Spirillum • Spiral  Spirochete • Helical  Pleomorphic • Vary in shape • Cells adhere tofether after cell division, especially cocci, this gives characteristic arrangements • Division along a single plane may result in pairs or chains of cells • Arrangement depends on plan of division o Pairs=diplococcic o Chains=streptococci  streptococcus • Division along two or three perpendicular planes for cubical packets o Sarcina genus • Division along several random planes form clusters o Staphylococcus • Some bacteria live in froups form specific multi-cellular associations o Myxobacteria  Form a swarm/gang of cells  When nutrients become limited the form the fruiting body • Other organisms for biofilm o Static in location o Extrapolmetric substances (EPS) o Dynamic community structure helps recruitment and survival in harsh condition Layers external to cell wall • Capsules and slime layer  Protection • Protects bacteria from host defenses  Attachment • Enables bacteria to adhere to specific surfaces o Capsule is a distinct • Cell wall o Determines shape of bacteria o Holds cell together o Prevents cell from bursting o
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