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Chapter 4: Microscopy and Cell Structure Resolution Limits to Resolving Power: Refractive Index Aberration: Early lenses were generally not homogenous glass and had variable refractive index across their surface, leading to distortion Types of Microscopes Brightfield Phase Contrast Light Differential Interference Contrast (DIC or Namarski) Darkfield Fluorescence Con-Focal Transmission EM Electron Scanning EM Atomic Force Microscopy (AFM) Principal of DIC (Differential Interference Contrast) OR Phase Contrast microscopy Highligts: Edges & Surfaces of objects Fluorescence Microscope Optic Train Microscope Comparison (Lens Trains) TEM vs. SEM TEM see internal structure can go to very high resolution --- down to about 5 nm directly (further with image averaging technique) --- down to about 0.2 nm (2 angstrom) with electron crystallography cannot see surface features separately see entire thickness of sample SEM see surface features only can do elemental analysis of scattered electrons lower resolution than TEM (around 100-200 nm) sample preparation more difficult (but generally fewer artifacts) Atomic Force Microscopy (AFM) Advantages: Range of resolutions Live specimens Cost Disadvantages: Image quality Time consuming Prokaryotic Cell Structure Cell Shape Rod/Bacillus Bent Rod/ Vibrio Spirillum (rigid helical shaped cell) Spirochete (flexible spiral cell, contains a flagellum between the cytoplamic membrane and outer membrane) “Multicellular” Prokaryotes actinobacteria form extensive networks of filaments that are all cytoplamically contiguous (although there is some barrier to free movement of material) filamentous cyanobacteria also form filaments, in some cases with cellular specialization Also keep in mind that most bacteria live in communities Cell Division Fission (generally symmetrical) Budding (distinctly asymmetrical) Fragmentation Internal Structures DNA Bacterial Chromosome (one DS molecule, haploid) Plasmids (replicate independently of chromosome) Transformation Horizontal Conjugation Transfer Transduction Ribosomes (60 S) rRNA & Protein, involved in translation Linked transcription & translation common in prokaryotes Gas vesicles Surrounded by protein sheath, used for buoyancy Storage particles (Store nutrients and essential elements) Glycogen/ Starch Poly-B-hydroxybutryic acid (PHB)
