Chap 3

• Organelles


  Subcellular structures that have one or more specific jobs to perform in the cell, much like an organ does in the body
• Chromosomes


  Thread-like structures made up of DNA, found in the nucleus of each cell
• In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
• Plasmid


  A small molecule of DNA that can reproduce independently
• Cytoplasm


  Everything between the plasma membrane and the nuclear envelope in eukaryotic cells. In prokaryotes, cytoplasm simply means everything found inside the plasma membrane.
• Plasma membrane


  A double layer of lipids that separates the cell interior from the outside environment
• Capsule


  • Many prokaryotes secrete a substance called glycocalyx (meaning sugar coat) on their surface
  • If the substance is organized and firmly attached to the cell wall, the glycocalyx is described as a capsule
  • Capsules confer resistance to phagocytosis

  
• Capsule staining


  • The background is formed with india ink or nigrosin or congo red
  • A positive capsule stain requires a mordant that precipitates the capsule
  • By counterstaining with dyes like crystal violet or methylene blue, bacterial cell wall takes up the dye. Capsules appear colorless with stained cells against dark background.

  
• Capsule vs slime layer

  Capsule has a semi-rigid border that follows the contour of the cell. Slime layer is a non-rigid matrix that is easily deformed and is not able to exclude India Ink.
• Functions of capsules and slime layers

  • Primary functions are for protection and adhesion
  • Capsules prevent the direct access of lysosome contents with the bacterial cell, preventing their killing
  • Capsules may protect bacteria from complement activation, so encapsulated bacteria are not immediately recognized as invaders by the phagocytes
• Cell wall


  Both Gram-positive and Gram-negative bacteria possess cell wall peptidoglycans, which confer the characteristic cell shape and provide the cell with mechanical protection
• Differences between Gram-positive and Gram-negative cell walls

  • The major difference involves the thickness of the layers surrounding the plasma membrane