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PSYC 2110
Gillian Wu

CH 3: THE PLASAM MEMBRANE AND MEMBRANE POTENTIAL MEMBRANE STRUCTURE AND COMPOSTION  The p.m. is a trilaminar structure which can only be seen using an electron microscope o There are 2 dark layers that surround a 3 light layer (this is bc the outer layers can be stained more than the inside nonpolar area which is lighter under an electron microscope) Plasma membrane (composition)  Phospholipids: the most abundant lipid in the membrane (have a non-polar tail and polar heads) o Made of a phosphate group (head) and 2 nonpolar fatty acid tails  Cholesterol: found in b/w the phospholipids – they are used to inhibit the fatty acids from binding and crystalizing (which wouldn’t allow the membrane to be so fluid) o Since the membrane is fluid, it is able to change shape when needed; i.e. muscle cells that contract or RBCells that change shape to fit through the capillaries  Membrane proteins: inserted in the lipid bilayer – proteins are larger than lipids so they account for half of the mass of the membrane, although there are 50 times more lipids  Fluid mosaic model: the membrane is fluid and looks mosaic bc of the different shaped proteins  Carbs: found only on the ECF portion of the p.m. (so the membrane is sugar coated) – only have glycoproteins and glycolipids (based on what there attached to): the carbs are used as self recognition molecules - discuss later Lipid bilayer (3 functions)  Structure of membrane  Hydrophobic interior: barrier for passage of water-soluble substances from the ECF – cell can maintain what goes in and out  Allows fluidity Membrane proteins – different specialized proteins are used for different fn’s  Channels: used for small, water-soluble things to pass without going through the nonpolar barrier – there are HIGHLY selective  Carrier molecules: transfer things across the membrane that cant go alone – can transport a particular molecule or one that resembles it  Docking-marker acceptors: found in the ICF and bind to secretory vesicles (lock and key) – allows secretion through exocytosis  Membrane-bound enzymes: control chemical rxns on both sides of the p.m. i.e. enzymes that destroy chemical messengers that trigger muscle contractions, so they can relax  Receptor sites: able to bind with a specific molecule (outside the cell) and alter activity in the cell  Cell adhesion molecules (CAMs): looks like loops protruding from the ICF to the ECF and can grip fibers on other cells – holds cells w/in tissue and organs together this way o CAMs also act as signaling molecules – signal cells to grow and interact w/ the right type of cells  Bind w/carbs (glycoproteins) for the cells ability to recognize “self” and in cell-to-cell interactions Self-recognition – glycoproteins and glycolipids  Allow cells to identify and interact w/each other in different ways:  Different cells have different markers based on their unique sugar chain – allows cells to recognize others that are their own kind – this allows the same type of cells to become tissues (especially important for embryo development)  Also allow for tissue growth – cells wont grow and trespass to neighbored cells (exception is cancer cells - they will invade the space of other cells) CELL-TO-CELL ADHESION  Allow cells to bind together and become tissue (which become organs) Biological “Glue”  ECM (extracellular matrix): fibrous proteins found in the interstitial fluid – used to hold neighbouring cells together (like glue)  Protein fibers are: o Collagen: cable-like fibers that provide tensile (resistance) to longitudinal stress – scurvy causes these fibers to not form, so tissue is fragile and leads to bleeding o Elastin: rubber like fiber which allows tissue to stretch and recoil (like the lungs) o Fibronectin: holds cells in position – cancer cells have reduced amounts of this which is why they can grow on top of each other and break loose and metastasize  The ECM is useful for creating different environments for different specialized cells and also allows for cell growth – only blood cells can survive and function without attaching to the ECM Cell Junctions  Cell adhesion molecules (surface proteins on the p.m) are used to hold the different cells together through 3 different types of junctions Desmosomes: anchor close distance cells together; ADHERING JUNCTIONS  Has 2 components – (1) dense button like thickenings (plaque) which is found on the inner surface of each cell and (2) glycoproteins which are used to attach the two plaques together Tight junctions: firmly bind to seal off a passageway b/w 2 cells  Found in epithelial cells – used to seal off the different internal cavities and the skin so bodily chemicals don’t mix together  Kiss sites: sites of tight seal around the border  The junction is impermeable – passage of things has to go through the cells, not b/w them (regulated by the channels and carriers) Gap Junctions: gap found b/ adjacent cells, which are linked by connexon’s  Connexon: a 6-protein subunit that creates a hollow tube like structure (A connexon from different cells will join to make a tunnel b/w the cells)  Only small water soluble particles can pass this way (ions and small particles can be exchanged without having to enter the ECF)  Found often in cardiac and smooth muscle – allows synchronized contractions of the muscles and heart  Also allow small nutrients to pass – glucose, a.a., etc. to things like a developing egg in the ovaries  Allows communication of cells OVERVIEW OF MEMBRANE TRANSPORT  Substances that can pass the membrane = permeable  Impermeable = cant pass the membrane  P.m. = selectively permeable (something’s can pass while others cant)  Things that are too big in size and not lipid soluble are able to only pass the membrane through assisted transport (i.e. glucose)  Something’s need a force to move (active) whereas some
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