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Lecture 3

PHYS 215 Lecture 3: Plasma Membrane and Membrane Potential

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PHYS 215
Kelly Worden

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1. Plasma Membrane and Membrane Potential Plasma membrane (Made up of phospholipid bilayer)  Components: o Lipid  Lipids are both hydrophobic (water fearing) and hydrophilic (water loving)  Phospholipid bilayer – hydrophilic head groups and hydrophobic tail groups line up o Protein  Think of plasma membrane as a sea of proteins and lipids  Integral proteins – penetrate the membrane  Peripheral proteins – sit on top  Roles of membrane proteins o Channels  Water – bipolar, oxygen with a net negative charge and hydrogen with a net positive charge, this is what makes water a good solvent  Ions – charged particles  Cations – positively charged  Anions – negatively charged  When a salt dissolves into water it separates into its cation and anion components o E.g. NaCl  Na+ Cl-  Bilayers are impermeable to ions, so proteins that allow the movement of ions are necessary  Calcium channels are made up of proteins that interact to for a tunnel through the membrane tat allows the transport of calcium  Movement of ions across membranes  Diffusion – the movement of ion down its electrical / chemical gradient o Fick’s Law of Diffusion  Dependent on:  Concentration gradients  Membrane permeability  Surface area  Molecular Weight  Membrane thickness  Pumps – movement of ions against the concentration gradient through the use of ATP o Carriers  Specificity  Saturation (Once all bound, that’s it – no more)  Competition  Types of carrier transport o Active transport – use of ATP (pumps) o Passive transport – use of electrical / chemical gradient  Facilitated diffusion – use gradients to move a molecule via a carrier across a membrane  Cotransport – use the gradient of one molecule to move another e.g. Na+ and glucose o Docking proteins (SNARE PROTEINS)  Two types:  v-SNARES o –VAMP (SNAP Debrivin SP?)  t-SNARES o –Syntaxin o –SNAP o Enzymes (Cuts, clips, or adds)  Kinases – ass phosphate groups (phosphorylation)  Phospholipases – convert phospholipids to fatty acids and other products  Acetylcholinesterase – can associate with plasma membrane, breaks down ACh o Receptors  Bind chemical messengers  Receptor may  Activate a channel  Receptors may be an enzyme  Receptors may activate a second messenger pathway o Adhesion molecules  Extracellular matrix  Collagen o Provide resistance to longitudinal stress o Scurvy  Elastin o Involved in stretching and recoiling o E.g. lungs  Fibronectin o Promotes cell adhesion  Cell adhesions molecules (CAMs)  Form loops or hooks that cell use to grip each other  Examples o Cadherin  Cell Junctions  Desmosomes o Anchor 2 non-touching cells o Plaque o Glycoprotein filament o Epithelial skin cells, cardiac muscle, uterus  Tight junctions o Direct interacting plasma membranes o Epithelial sheets o Digestive tract (prevent acid from getting in body)  Gap junctions
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