Attachment to ECM Cell cell recognition Intercellular joining Receptors for

Attachment to ecm cell cell recognition intercellular

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Attachment to ECM Cell-cell recognition Intercellular joining Receptors for signal transduction Enzymatic activity Transport
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4 Functions of the plasma membrane 1. Physical barrier: Encloses the cell, separating the cytoplasm from the extracellular fluid. 2. Selectively permeable: Determines which substance enter or exit the cell. 3. Communication: Plasma membrane proteins interact with specific chemical messengers and relay messages to the cell interior. 4. Cell recognition: Cell surface carbohydrates allow cells to recognize each other. Transport across the plasma membrane •substance can cross the plasma membrane in 2 different ways: -Active process (The cell provides energy (ATP) needed to move substances across. Substance can move from low to high concentration.) -Passive process (substances cross the membrane without energy (ATP) input from the cell. Substances move from high to low concentration.) * Concentration: The bigger the difference in concentration of the diffusing molecules or ions between the 2 areas, the more collisions occur and the faster the particles diffuse. * Molecule size: Smaller molecules diffuse more rapidly. * Temperature: Higher temperature (more kinetic energy) increases the speed of molecular movement and means more rapid diffusion. 4 types of passive transport •Simple diffusion: Substances diffuse directly through the lipid bilayer. Small nonpolar molecules that dissolve in water (lipid soluble). EX: Gases (O2 and CO2), steroid hormones, and fatty acids. EX: Water is not lipid soluble and you would expect it to be pushed back by the hydrophobic lipid tails; however, because it is very small, small amounts can move across the lipid bilayer by simple diffusion. Facilitated diffusion: The molecules (glucose, sugars, some amino acids, and ions) move through the membrane in which the transported substance either binds to carrier proteins in the membrane and is carried across (carrier-mediated) or moves through water-filled channel proteins (channel-mediated). - Carrier-mediated facilitated diffusion: Specific for transporting certain polar molecules (sugars and amino acids) that are too big to pass through membrane channels. Envelop and then release, allowing it to bypass the nonpolar regions. EX: When all the glucose carriers are busy, they are saturated, and glucose transport is occurring at its maximum rate.
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- Channel-mediated facilitated diffusion: specific for transporting ions or water, through aqueous channels from one side of the membrane to the other. Channels are selective due to pore size. Some channels are always open (leakage channels) and some are controlled by chemical or electrical signals (gated channels). Osmosis: Diffusion of a solvent like water through a specific channel protein or through the lipid bilayer.
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  • Fall '08
  • CARNEGIE
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