Transcript Structure
CELLULAR TRANSPORT The Gate-Keeper of the Cell THE CELL MEMBRANE •REMEMBER…The cell membrane controls the movement of substances into and out of the cell (selectively permeable) THE CELL MEMBRANE • Separates cell from environment & regulates what enters and leaves • It mainly consists of: – phospholipid bi-layer – embedded proteins – glycoprotiens 1. THE PHOSPHOLIPID BI-LAYER • Structure: – 2 layers of phospholipid molecules • Function: Mmm… Water Mmm… Oil – Keeps cell intact – Hydrophilic heads and Hydrophobic tails regulate what enters and leaves the cells. 2. PROTEINS • Structure: – embedded randomly in membrane • Function: – Transport larger items through the membrane – Allow hydrophilic particles through. 3. GLYCOPROTEINS • Structure: – Proteins with attached sugar molecules. • Function: – Attachment sites for molecules needing to enter, or for messenger molecules such as hormones. – These are very specific to each person and play a role in recognizing our own cells (organ transplants) PASSIVE TRANSPORT - “COME ON AND TAKE A FREE RIDE” No ATP (energy) needed ATP = Energy Currency of the cell!!! There are three types: 1. DIFFUSION -Small molecules (CO2, H2O, O2, salts) can move between the phospholipid molecules of the bilayer. -Molecules move from a HIGH concentration ([]) to a LOW [] along a CONCENTRATION GRADIENT until a balance is achieved. Diffusion Passive Transport 2. OSMOSIS -The movement of water (from High to Low [ ]) through a selectively permeable membrane. Osmotic Conditions Surrounding Cells Isotonic solution – Solute [ ] outside of cell is equal to [ ] inside the cell. Hypertonic solution – Fluid surrounding the cell has a higher solute [ ] than inside. Hypotonic solution – [ ] of solute is higher inside the cell than outside. What will happen to a cell if placed in each of these conditions??? Come up with an answer! Passive Transport •Osmosis is a VITAL fluid control process (blood and urine balance) Passive Transport 3. FACILITATED DIFFUSION -Some proteins in the cell membrane provide a “tunnel” for larger molecules (glucose) to diffuse through. -They go with the concentration gradient! ACTIVE TRANSPORT • ATP is the energy used to “pump” nutrients across cell membranes. • Using ATP, carrier proteins “pump” substances through a membrane from an area of LOW [ ] to an area of HIGH [ ] against the concentration gradient. • Eg. Na+/K+ pump in nerve cells ACTIVE TRANSPORT A QUESTION! HOW DO THE REALLY LARGE MOLECULES (Hormones, polysaccharides etc.) move in and out of cells?? An Answer!! By two processes called ENDOCYTOSIS AND EXOCYTOSIS. Both methods require the use of vesicles and ATP! ENDOCYTOSIS –Moving materials into the cell Three Types… 1. Phagocytosis (Cell Eating): -Used by white blood cells and amoeba. -The cell moves out and surrounds the solid particle. ENDOCYTOSIS –Moving materials into the cell 2. Pinocytosis (Cell drinking) -Same process as phagocytosis except the cell is moving liquids. ENDOCYTOSIS –Moving materials into the cell 3. RME – Receptor Mediated Endocytosis -E.g. Moving cholesterol into the cell (or Hypercholesterolemia) EXOCYTOSIS – Moving materials out of the cell •The reverse of pinocytosis •The vesicle (from the Golgi) fuses with the membrane and releases it’s contents out of the cell. •E.g. Hormones ANY QUESTIONS??? The End!!!