CH5

• Fluid-Mosaic Model

  Plasma membrane is composed of a fluid phospholipid bilayer with wholly or partially embedded protein molecules
• Plasma membrane structure

  A bilayer of phospholipids with partially or wholly embedded proteins
• Plasma membrane function:

  Separates internal environment of a cell from external environment

  Regulates the exit and entrance of molecules

  Stabilize internal environment
• Phospholipids

  Amphipathic molecules with hydrophilic head and hydrophobic tails
• Cholesterol

  Lipid found in animal plasma membranes that strengthens the membrane and regulates fluidity
• Proteins in plasma membrane

  • Peripheral proteins (found on inner cytoplasmic surface)
  • Integral proteins (partially or wholly embedded in the membrane)
• Extracellular matrix (ECM)

  Made of proteins and large complex carbohydrates, it supports the plasma membrane and communicates between cells
• Fluid-Mosaic Model

  • Fluidity of membrane is due to lipid content
  • Mosaic nature is due to protein content
  • Some proteins move freely, others are held by cytoskeleton or ECM
• Glycocalyx

  Sugar coat of carbohydrate chains on animal cell surfaces that protects cells, eases adhesion, receives signals, and enables cell-cell recognition
• Each cell has a unique glycocalyx due to variation in number, sequence, and branching of carbohydrate chains
• Glycolipids

  Phospholipids with carbohydrate chains
• Glycoproteins

  Proteins with carbohydrate chains
• Carbohydrate chains occur only on the outside of the plasma membrane, making the two sides asymmetrical
• Transplanted tissue is often rejected because the immune system recognizes foreign carbohydrate chains, histocompatibility proteins, and recognition proteins
• Functions of integral proteins

  • Channel proteins
  • Carrier proteins
  • Cell recognition proteins
  • Receptor proteins
  • Enzymatic proteins
  • Junction proteins
• Peripheral proteins

  Have a structural role in stabilizing and shaping the plasma membrane
• Permeability of plasma membrane

  • Selectively permeable
  • Some molecules pass freely, others need carrier/channel proteins and/or energy
  • Small non-charged lipid soluble molecules pass freely
  • Small polar molecules like water pass easily down concentration gradient
  • Ions and charged molecules have difficulty crossing and require carrier proteins
• Passive transport

  Moves molecules across membrane down concentration gradient without energy expenditure, includes diffusion and facilitated transport
• Active transport

  Requires carrier proteins and uses energy (ATP) to move molecules against concentration gradient
• Diffusion

  Movement of molecules from higher to lower concentration down their concentration gradient
• Osmosis

  Diffusion of water across a differentially permeable membrane
• Tonicity

  Strength of a solution in relation to osmosis
• Isotonic solution

  Relative solute concentrations of two solutions are equal
• Hypotonic solution

  Solute concentration less than another solution, can cause cells to burst
• Hypertonic solution

  Higher percentage of solute than a cell, can cause cells to shrink
• Plasmolysis

  Shrinking of plant cell cytoplasm due to osmosis in a hypertonic situation
• Exocytosis

  Transport of molecules from cell to outside, vesicles fuse to plasma membrane and excrete to outside
• Endocytosis

  Transport of molecules from outside cell to inside, cells take in substances by vesicle formation (phagocytosis, pinocytosis, receptor-mediated endocytosis)
• The shrinking of cell in salted meat

  crenation
• In animals cell shrinking of cell due to hypertonic

  crenation
• Source of vesicles for exocytosis

  Golgi body
• What happens in both exocytosis and endocytosis

  Involve vesicles

  Transport large molecules

  Occur at cell membrane
• Regulated secretion

  Specific needs for body triggering vesicles to fuse with the plasma membrane
• What structure is made by the cell to transport large substance in and out of the cell

  Vesicles
• Vesicles that ensure macromolecules during exocytosis are composed of

  Phospholipid bilayers