01:119:116 Lecture Notes - Lecture 2: Crystal Violet, Gram Staining, Safranin
22 Apr 2016
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Document Summary
Chemical evolution hypothesis life developed from non-living matter. Divided in two domains: bacteria and archaea. Pervasive found everywhere / every environment. Size most are ~0. 5 - 5 um (eukaryotic cells 10-100 um) Spirals = spirillum (if rigid), = spirochete (if flexible) Cell wall: feature of almost all prokaryotes. Prevents it from bursting in an hypotonic environment. Doesn"t prevent from plasmolysing in hypertonic environment cell loses water and shrinks. Archaea contains polysaccharides and proteins but lack peptidoglycan. Scientists use the gram stain to classify bacteria by cell wall composition. Two stains used: crystal violet (purple) and safranin (pink) Thick cell walls made primarily of peptidoglycan. Cell wall made of thin peptidoglycan layer. Crystal violet rinsed away, safranin picked up. Also thick outer membrane of lipopolysaccharides (lps) Capsule more organised and tightly associated. Fimbriae generally shorter and more numerous than pili. Allow to stick to substrate or others in a colony. Pili (or sex pili) are longer than fimbriae.
