BIO 101 1st Edition Lecture 7 Outline of Last Lecture I Carbohydrates a Monosaccharide i Ring Structures b Disaccharide c Polysaccharide i Storage ii Structural Outline of Current Lecture I Cytoplasmic Membrane II Fluid Mosaic Model a Proteins b Carbohydrates c Cholesterol III Small Molecules Across the Membrane a Transport Proteins IV Diffusion Current Lecture Chapter 7 Membrane Structure and Function Cytoplasmic or plasma membrane boundary that separates the living cell from its nonliving surroundings A barrier but more than that it controls the traffic into and out of the cell Selectively permeable lets some things pass but not others The unique structure of the membrane makes life possible These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute FLUID MOSAIC MODEL of membrane structure The membrane is a mosaic of different macromolecules The BASE STRUCTURE is a bilayer of phospholipids Hydrophobic H2O fearing fatty acid tails in the center Polar heads of phospholipids are hydrophilic H2O loving They face toward the inside and the outside of the cell Many other molecules associate with the base PHOSPHOLIPID BILAYER Proteins the functions of the membrane are primarily determined by the proteins that associate with it 2 major kinds of membrane proteins o Integral Membrane proteins embedded in the phospholipid bilayer with hydrophobic parts of the protein interacting with the hydrophobic middle of the bilayer some integral membrane proteins stick out only to the outside of the cell others only to the inside of the cell unilateral integral membrane proteins Some stick out on both sides of the bilayer transmembrane integral membrane proteins o Peripheral membrane proteins not actually embedded in the phospholipid bilayer but stuck onto another molecule that is embedded in the bilayer Carbohydrates carbohydrates associated with the membrane serve in cell cell recognition usually face to the outside of the cell where they act as molecule ID tags Carbohydrates covalently bound to proteins glycoproteins Carbohydrates bound to lipids glycolipids Cholesterol a lipid embedded in hydrophobic middle of the membrane affects the fluidity of the membrane o the membrane is bifacial it looks different from the inside than it does from the outside The Fluid Nature of the Membrane the membrane is not a rigid static structure the phospholipids move around rapidly very dynamic membrane has a consistency about like salad oil the fluid nature is important for proper function Traffic of Small Molecules across the Membrane the hydrophobic middle of the membrane is the main barrier to molecules moving across small hydrophobic nonpolar molecules move easily because hydrophobicity is not a barrier to them hydrophilic polar molecules have a harder time o small hydrophilic molecules ex H2O CO2 get across the membrane by passing BETWEEN phospholipid molecules o larger hydrophilic molecules ex sugars and ions charged atoms or molecules get across the membrane using Transport Proteins integral transmembrane proteins that move particular molecules across the membrane 2 Basic Kinds of Transport Proteins 1 channels provide a hydrophilic tunnel through the membrane the tunnel is specific for a particular molecule or related molecules 2 carrier proteins hold onto specific molecules and then change shape to shuttle them across the membrane Diffusion Much of the traffic of molecules across the membrane occurs by diffusion Diffusion net movement of a substance DOWN its concentration gradient substance diffuses from where it is MORE concentrated to where it is LESS concentrated each substance diffuses down its own concentration gradient not affected by the concentration gradients of other substances Diffusion is a spontaneous process The energy for movement comes from the concentration gradient Passive Transport diffusion across a biological membrane Osmosis diffusion of H2O across a membrane
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