Plasma Membranes. CN: page 22 Eq : How does the structure of a membrane enable it to control what goes in & out of cell. EARLY FLUID MOSAIC MODEL. UPDATED MODEL of ANIMAL CELL PLASMA MEMBRANE. PHOSPHOLIPID BILAYER. HOW TO MAKE A PHOSPHOLIPID. GLYCEROL . + phosphate group = “head”.
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Plasma Membranes CN: page 22 Eq: How does the structure of a membrane enable it to control what goes in & out of cell
Cholesterol’s Effect @ 37ºC cholesterol makes membrane less fluid by restraining phospholipid movement lowers temp required for membrane to solidify
Membrane Proteins • >50 membrane proteins • 2 main categories: • Integral Proteins • penetrate the hydrophobic inside of lipid bilayer • most are transmembrane proteins • Peripheral Proteins • appendages loosely bound to either surface
Membrane Proteins on cytoplasmic side some proteins held in place by attachment to cytoskeleton on ECF side some proteins attached to fibers in extracellular matrix both give animal cells stronger framework
Major Functions of Membrane Proteins TRANSPORT provides hydrophilic channel thru hydrophobic interior of lipid bilayer some use passive some active transport
Major Functions of Membrane Proteins 2. ENZYMATIC ACTIVITY all enzymes are proteins so a membrane protein could have all or part of its structure function as an enzyme in some membranes several enzymes organized to carry out sequential steps in a metabolic pathway
Major Functions of Membrane Proteins 3. SIGNAL TRANSDUCTION membrane protein acts as receptor has binding site with specific shape that exactly fits shape of the chemical messenger (signal molecule or ligand) when signal enters receptor site usually the membrane protein changes shape (configuration) which relays message into cell, usually binding to a cytoplasmic protein
Major Functions of Membrane Proteins 4. CELL-CELL RECOGNITION some glycoproteins act as ID tags recognized by membrane proteins of other cells which may bind to them attachment short-lived
Major Functions of Membrane Proteins 5. INTERCELLULAR JOINING membrane proteins of adjacent cells may hook together in different types of cell jcts tends to be long-lasting
Major Functions of Membrane Proteins 6. ANCHORING cytoskeletal elements may be noncovalently bound to membrane proteins: helps maintain cell shape & stabilizes location of membrane proteins
Cell Surface Proteins medically important: some pathogens use them to adhere/enter cell some medications designed to take advantage of using them
Glycocalyx • glycoproteins + glycolipids • usually ~15 sugar units • exterior surface of cell membrane • key to cell-to-cell recognition • sorting cells in embryo • Immune System
Selective Permeability plasma membrane example of emergent properties: each individual membrane protein, lipid, or carb together become a “supermolecule”
Selective Permeability essential to cell’s existences Fluid Mosaic Model helps explain how regulation occurs 24/7 steady stream on ions & small molecules in/out cell; each at their own rate
Selective Permeability depends on: lipid bilayer specific transport protein built into membrane
Selective Permeability In general: small, nonpolar molecules get in ions and polar molecules don’t get in
Transport Proteins hydrophilic substances get thru hydrophobic lipid bilayer by going thru center of a transmembrane, transport protein
Channel Proteins • hydrophilic channel • hydrophobic a.a. in portion of protein that interfaces with lipid bilayer • Aquaporins: allow water molecules to cross • channel open, allows up to 3 billion water molecules/s • water follows its concentration gradient by osmosis
Carrier Proteins attach to their “passenger” change in shape so that passenger is shuttled thru membrane very specific: 1 substance or small group of similar substances
Passive Transport is diffusion of substance across membrane w/no nrg investment
Diffusion • In the absence of other forces, a substance will diffuse from where it is more concentrated to where it is less concentrated. (it will move down its concentration gradient) • No work required: spontaneous because particles have KE and are in constant motion • ex: O2 & CO2
Facilitated Diffusion • channel or carrier proteins that allow hydrophilic substances to cross membranes moving down their concentration gradients • if transport ions called ion channels • many are Gated Ion Channels • open/close mechanism works in response to stimuli (electrical, specific ligand)
