chapter 4: cell structure/function. compound light microscopy
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Chapter 4:Cell Structure/Function
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Compound Light MicroscopyCompound Light Microscopy
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Compound Light MicroscopyCompound Light Microscopy•Magnification
•Resolution capacity to distinguish as separate 2 adjacent points. Max resoultion of light microscope is 0.2 micrometers (2 points closer than 0.2 apart appear as one)
•Refractive Index measure of speed at which light passes through a material (staining increases the difference between refractive indexes of specimen and the medium…so contrast is increased)
•Brightfield illumination
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Some microorganisms are pigmented. Most are not.
Green algae
Purple phototrophic bacteria
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StainingStaining• Basic dyes (positive ion colored)
Positive stains
• Acidic dyes (negative ion colored)
Negative stains
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Steps in smear preparation and staining
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The Gram Stain
(a differential stain)
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Gram Stain…Positive cocci and Negative rods
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Darkfield microscopyDarkfield microscopy(specimem appears light against a black (specimem appears light against a black background)background)(good for seeing motility and very small or thin (good for seeing motility and very small or thin microbes)microbes)
Phase ContrastPhase Contrast(enhances differences in refractive indexes of (enhances differences in refractive indexes of structures, so…yields increase contrast) (good for structures, so…yields increase contrast) (good for seeing internal structures of living cells)seeing internal structures of living cells)
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DarkfieldPhase contrastBrightfield
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Cyanobacteria stained with fluorescent dye
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Three-Dimensional Three-Dimensional ImagingImaging
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Differential Interference Differential Interference Contrast MicroscopyContrast Microscopy
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Atomic Force Microscope (AFM)
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Confocal Scanning Laser Confocal Scanning Laser MicroscopyMicroscopy
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Electron MicroscopyElectron Microscopy
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TEM Transmission Electron Microscopy
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SEM Scanning Electron Microscopy
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CELL SIZE
(an upper limit is imposed by surface to volume ratio)
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Prokaryotes and Eukaryotes Prokaryotes and Eukaryotes comparedcompared
• Similarities– Genetic material– Cellular chemistry and metabolic pathways– Some structures and functions
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Prokaryotes and Eukaryotes Prokaryotes and Eukaryotes comparedcompared
• Differences (compartmentalization)– Prokaryotes
• DNA NOT enclosed by membrane• No membrane-bound organelles• No histone proteins associated with DNA• Complex cell walls• Division by binary fission
– Eukaryotes• DNA with a nucleus• Membrane-bound organelles• Histone proteins• Cell walls absent or simple• Division by mitosis
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BASIC SHAPES
•Coccus
•Rod
•Spiral
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CELL STRUCTURESCELL STRUCTURES
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Cytoplasmic MembraneCytoplasmic Membrane
•Phospholipid bilayer studded with proteins (Fluid Mosaic Model)
•Selectively permeable barrier
•Membrane strengthening agents
•Sterols in eukaryotes
•Hopanoids in some bacteria
•Archaea contain very different lipids than Eukarya and Bacteria
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Transport across Transport across membranesmembranes
Passive processes
Diffusion/osmosis
Facilitated diffusion
Active processes
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Cell WallCell Wall•Peptidoglycan
• A polysaccharide which is the major component of cell walls in bacteria
• Archaea cell walls do not contain peptidoglycan
• Structure: Polysaccharide chains (glycans) cross-linked by peptide chains of amino acids.
•Two subunits N-Acetylglucosamine (G) and N-Acetylmuramic acid (M)
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Gram Positive Cell Wall•Thick layer peptidoglycan
•Teichoic acid
• Lipoteichoic acid
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Gram Negative Cell wall• Outer Membrane
• LPS-lipopolysaccharide (Endotoxin)
• Porins
• Periplasm
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Genetic MaterialGenetic Material
• Nucleoid = area of the cell in which the DNA is aggregated
• Single circular chromosome
• Haploid
• Plasmids
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MotilityMotility
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FlagellaFlagella
•Filament
•Hook
•Basal Body
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Rotational movement of the flagella
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Peritrichous Polar (monotrichous)
Polar (lophotrichous)
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TaxisTaxis
• Phototaxis
• Chemotaxis
Positive taxis
Negative taxis
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Phototaxis: Figure shows movement of an entire colony of bacteria toward a light source at the right of the photo (not shown)
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RibosomesRibosomes
• Site of protein synthesis
• Some structural differences between prokaryotic and eukaryotic ribosomes
• A major site of attack for antibiotics
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Surface StructuresSurface Structures
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Fimbriae and PiliFimbriae and Pili
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S-LayersS-Layers
A surface layer made of protein found in many bacteria
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Capsules and Slime LayersCapsules and Slime Layers
Glycocalx – polysaccharide-containing material outside of the cell
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Inclusions/Storage Inclusions/Storage Bodies/GranulesBodies/Granules
Function in storage of energy molecules or as a reservoir of structural building blocks
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PHB (poly-B-hydroxybutric acid)PHB (poly-B-hydroxybutric acid)
A carbon/energy storage polymer
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• Glycogen (energy storage)
• Metachromatic granules (inorganic phosphate reserves)
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Sulfur Granules
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Magnetosomes
Iron-oxide crystals which allow the bacteria to respond to a magnetic field
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Gas VesiclesGas VesiclesSmall gas filled protein structures that function to confer bouyancy on cells
EM of gas vesicles
Cyanobacteria “bloom” on lake surface
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EndosporesEndospores• Hardiest of all life forms
• For escape from unfavorable environmental conditions
• Germination = return to the vegetative state from the spore state
• NOT reproductive (1 cell forms 1 endospore which return to reform 1 cell)
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Endosymbiont theory of Eukaryotic Endosymbiont theory of Eukaryotic evolutionevolution
Evidence in support of the hypothesis• Mitochondria and chloroplasts contain their own
DNA• They contain their own ribosomes which are
very similar to prokaryotes• They divide independent of the cell and by
binary fission• Size, etc. etc