Membrane Structure & Function

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Membrane Structure & Function
2010-10-19 20:07:51
AP Biology

Enzymes, Diffusion
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  1. The Plasma Membrane
    • the fluid mosaic model
    • semi-permeable
    • fluid portion is a double layer of phospholipids, called the phospholipid bilayer
  2. Jobs of the Cell Membrane
    • Isolate the cytoplasm from the external environment
    • Regulate the exchange of substances
    • Communicate with other cells
    • Identification
  3. Phospholipid Bilayer
    • Phospholipids contain a hydrophilic head and a nonpolar hydrophobic tail.
    • Hydrogen bonds form between the phospholipid "heads" and the watery environment inside and outside of the cell.
    • Hydrophobic interactions force the "tails" to face inward
    • Phospholipids are not bonded to each other, which makes the double layer fluid.
    • Cholesterol embedded in the membrane makes it stronger and less fluid.
  4. Proteins Embedded in Membrane Serve Different Functions
    • 1. Channel Proteins - form small openings for molecules to difuse through
    • 2. Carrier Proteins- binding site on protein surface "grabs" certain molecules and pulls them into the cell
    • 3. Receptor Proteins - molecular triggers that set off cell responses (such as release of hormones or opening of channel proteins)
    • 4. Cell Recognition Proteins - ID tags, to idenitfy cells to the body's immune system
    • 5. Enzymatic Proteins - carry out metabolic reactions
  5. Transport Across Membrane
  6. Passive Transport
    Simple Diffusion - water, oxygen and other molecules move from areas of high concentration to areas of low concentration, down a concentration gradient.

    Facilitation Diffusion - diffusion that is assisted by proteins (channel or carrier proteins)
  7. Osmosis
    • diffusion of water. Salt Sucks
    • Osmosis affects the turgidity of cells, different solution can affect the cells internal water amounts
    • Contractiles Vacuoles are found in freshwater microorganisms - they pump out excess water
    • Turgor pressure occurs in plants cells as their central vacuoles fill with water.
  8. Active Transport
    - involves moving molecules "uphill" against the concentration gradient, which requires energy
  9. Endocytosis
    - taking substances into the cell (pinocytosis for water, phagocytosis for solids
  10. Exocytosis
    - pushing substances out of the cell, such as the removal of waste
  11. Sodium-Potassium Pump
    - pumps out 3 sodiums for ever 2 potassium's taken in against gradient