BIOL 005B Lecture Notes - Lecture 2: Crystal Violet, Safranin, Genetic Recombination
Document Summary
Biol 005b lecture 2: prokaryote diversity: bacteria and archaea. Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or. Most prokaryotes are unicellular, although some species form colonies. Most prokaryotic cells are 0. 5-5 m, much smaller than the 10-100 m of many eukaryotic cells. Prokaryotic cells have a variety of shapes. Eukaryotic cell walls are made of cellulose or chitin. Bacterial cell walls contain peptidoglycan , a network of sugar polymers. Archaea contain polysaccharides and proteins but lack peptidoglycan. A polysaccharide or protein layer called a capsule covers many prokaryotes. Scientists use the gram stain to classify bacteria by cell wall composition. Gram-positive bacteria have simpler walls with a large amount of peptidoglycan. Peptidoglycan traps crystal violet, which masks the safranin dye. Gram-negative bacteria have less peptidoglycan and an outer membrane. Gram-negative bacteria are more likely to be antibiotic resistant. Crystal violet is easily rinsed away, revealing the red safranin dye that can be toxic.
