* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download topic-3.doc
Survey
Document related concepts
Cytokinesis wikipedia , lookup
Signal transduction wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cell membrane wikipedia , lookup
Cell culture wikipedia , lookup
Tissue engineering wikipedia , lookup
Cellular differentiation wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Endomembrane system wikipedia , lookup
Cell encapsulation wikipedia , lookup
Transcript
Today: Microscopes (Ch. 3), begin Prokaryotic cells (Ch. 4) Ch. 3 - Microscopes Total magnification: calculated by multiplying the objective lens magnification by the ocular lens magnification Resolution: ability to distinguish between two points a specified distance apart micrometer: 10-6m nanometer: 10-9m Light Microscopy Bright-field microscope: dark image against a brighter background Dark-field microscope: only refracted light enters objective, making specimen bright, background dark (useful for observing living cells, particularly spirochetes) Phase-contrast: converts slight changes in refraction into easily detected variations of light intensity (useful in observing living cells) Fluorescence: specimen exposed to ultraviolet light, compounds in the sample fluoresce, giving off visible light Electron Microscopy Uses electrons as illumination source (shorter wavelength allows greater resolution) Two types: o Transmission (TEM): electrons pass through thin section of specimen o Scanning (SEM): image produced by electrons which are emitted from the surface of an object Staining Fixation: process by which internal and external structures of cells are preserved o Heat-fixation - fix an air-dried thin film (smear) by passing through flame Dyes: have chromophore groups (give color) and bind to cells by ionic, covalent, or hydrophobic bonding o Ionic stains Basic dyes Acid dyes o Hydrophobic - Sudan black, stains lipids Stains Simple Stain: uses one staining agent Differential Stain: divides bacteria into separate groups based on different staining properties Gram stain most important staining procedure Dr. Christian Gram, 1884 o Procedure: Crystal Violet - 1 minute Gram's Iodine - 1 minute Decolorize with 95% ethanol (5-10 sec), Rinse Safranin - 1 minute Stains (continued) Gram stain (continued) o Gram positive - traps crystal violet-iodine complex, due to thick layer of peptidoglycan in cell wall PURPLE o Gram negative - large amount of lipids in cell wall are dissolved by the 95% ethanol, allowing crystal violet-iodine complex to escape, must add counterstain to colorless cells RED Stains (continued) Acid-fast stain: o used to stain Mycobacterium, which have high mycolic acid content (waxy) o Must use steam heat to force carbolfuchsin stain into cells o Acid-alcohol decolorizer removes stain from non-acid fast cells o counterstain with methylene blue Negative/Capsular stain: o reveals capsule layer around cells o mix bacteria with nigrosin, spread on clean slide, dry o useful to observe Klebsiella pneumonia Stains (continued) Spore stain: used to stain endospores of Clostridium and Bacillus o endospores do not readily take up dye, but once it penetrates the stain is not easily decolorized o heat smear over steam, rinse with water o counterstain with safranin o Endospores - Green; Vegetative cells - Red Flagellar stain: flagella of bacteria are coated with tannic acid or potassium alum and stained with basic fuchsin (Gray Method) Ch. 4 - Procaryotic and Eucaryotic Cells General Differences o Procaryotes generally smaller (0.2 - 2 microns diameter and from 2-8 microns in length) no nucleus or other membrane bound organelles one circular chromosome (most) no histone proteins associated with DNA cell wall generally contains peptidoglycan (complex polysaccharide) divide by binary fission Procaryotic and Eucaryotic Cells (continued) General Differences (cont.) o Eucaryotes large cells "true nucleus" and other membrane bound organelles multiple linear chromosomes histone proteins always associated with DNA cell wall does not contains peptidoglycan) divide by mitosis (complex process) Prokaryotic Cells: Shape and Arrangement Cell (Plasma) membrane Structure: o phospholipid bilayer (hydrophilic head and hydrophobic core) o contains embedded proteins o fluid mosaic model o some infoldings related to photosynthesis (known as thylakoids or chromatophores) Permeability: o semi-permeable layer small molecules and water pass freely charged molecules and larger ones cannot pass Moving materials across the membrane: Osmosis Osmosis: diffusion of water across a semi-permeable membrane Osmotic pressure: internal pressure which equalizes water movement in and out of a cell Solutions relative to cell solute concentration: o isotonic: equal solute concentration o hypotonic: lower concentration of solutes o hypertonic: higher concentration of solutes Transport Passive: o simple diffusion o Facilitated diffusion: protein mediated, no energy involved Active: o Active transport: energy used to bring in molecules o Group translocation: active transport where molecule is modified during transport (example: phosphorylation)