BIOL 1441 1st Edition Lecture 11 Outline of Last Lecture I Organelles II Cytoskeleton III Extracellular components Outline of Current Lecture I Plasma membrane a Fluidity b Cholesterol II Membrane proteins a 6 major functions III Permeability of the lipid bilayer a Polar vs nonpolar b Transport proteins IV Types of transport a Diffusion b Osmosis Current Lecture I Plasma Membrane a Boundary that separates living cell from its environment b Selective permeability allowing some substances to cross it more easily than others 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 II i Selective based on chemical properties c Cellular Membranes i Composed of lipids mostly proteins carbohydrates 1 Phospholipids most abundant lipid in the plasma membrane ii Amphipathic molecules containing hydrophobic hydrophilic regions d Fluid Mosaic Model i Membrane is a fluid structure with a mosaic of various proteins phospholipids embedded in it e Fluidity of Membranes i Phospholipids in the plasma membrane can move within the bilayer fluid as salad oil 1 Held in place by hydrophobic interactions weak ii Lipids some proteins drift laterally iii Rarely molecule flip flop across the membrane iv As temperatures cool membranes switch from a fluid state to a solid state 1 Molecules start slowing down and pack tightly together into a solid v Temperature where membrane solidifies depends on types of lipids fatty acids vi Membranes rich in unsaturated fatty acids are more fluid at lower temperature than saturated fatty acids 1 CANT FORM SOLID IF IT INCREASES UNSATURATED FATS B C OF KINKS IN THE TAIL 2 UNSATURATED FAT CARBON TO CARBON DOUBLE BONDS KINKS IN TAIL f Cholesterol i Cholesterol steroid effects membrane fluidity depending on the temperature ii Warm temperatures restrains movement of phospholipids making them less fluid 1 MOLECULES HAVE A LOT OF KINETIC ENERGY CHOLESTEROL ACTS AS A SPEED BUMP AND SLOWS THE MOLECULES DOWN iii Cool temperatures maintains fluidity by preventing tight packing 1 CHOLESTEROL INSERTS ITSELF BETWEEN TAILS TO KEEP THEM FROM PACKING TOO TIGHTLY FROM FORMING A SOLID TO MAINTAIN FLUIDITY 2 Lowers the temperature required for a membrane to solidify Membrane Proteins a Proteins in the plasma membrane can move b Different types of cells have different types of proteins in their plasma membrane c Integral protein penetrate the hydrophobic core of the lipid bilayer III IV i Transmembrane protein spans the entire membrane ii INSERTS ITSELF d Peripheral protein not embedded in the membrane bound to it i CAN BE ATTACHED TO A PROTEIN OR A PHOSPHOLIPID e 6 Major Functions of Membrane Proteins i Transport ii Enzymatic activity iii Signal transduction iv Cell cell recognition all cells in your body have markers that identify that it is you 1 Cells recognize each other by binding to surface molecules 2 Recognize self vs non self pathogens transplant tissue 3 Surface molecules usually carbohydrates a Covalently bonded to lipids glycolipids glycol tiny sugar attached to lipids a big lipid b Covalently bonded to proteins glycoproteins 4 Markers on your blood cells a Type A B AB or O v Intercellular joining vi Attachment to the cytoskeleton and ECM Permeability of the Lipid Bilayer SIZE CHARGE ARE IMPORTANT a Hydrophobic nonpolar molecules dissolve in the lipid bilayer pass through the membrane rapidly i O2 CO2 hydrocarbons ii Hydrocarbons nonpolar b Hydrophilic polar molecules do not cross the membrane easily i Sugars glucose ions water ii CROSS THROUGH MEMBRANE PROTEIN B C POLAR AND BIG MOLECULES CANT MOVE THROUGH FAST ENOUGH c Transport Proteins i Allow passage of hydrophilic substances very specific ii Channel proteins hydrophilic channel that specific molecules or ions can use as a tunnel 1 Opens up to let It in and shuts after pore 2 Aquaporins facilitate the passage of water iii Carrier proteins bind to molecules and change shape to shuttle them across the membrane 1 Attaches to molecule and drops it off on the other side of membrane Types of transport a Passive diffusion high to low natural i Channel proteins 1 Aquaporin or ion channel ii Carrier proteins iii HYDROPHOBIC SUBSTANCES DIFFUSE RIGHT ACROSS MEMBRANE DON T NEED TRANSPORT PROTEINS b Active low to high not natural have to use energy i ONLY carrier proteins c Passive Transport Diffusion i Thermal motion heat movement of molecules ii Diffusion molecules spread out evenly into the available space NATURAL MOVEMENT OF ANYTHING FROM HIGH TO LOW CONCENTRATION DOESN T HAVE TO BE ACROSS A MEMBRANE 1 Each molecule moves randomly Brownian Motion a EVERYTHING HAS MOVEMENT 2 All the of molecules movement in one direction iii Molecules move HIGH concentration to LOW concentration 1 Equally spread throughout d Factors that Affect Diffusion AFFECTS THE RATE OF DIFFUSION i Heat increase heat increase molecular collisions increase diffusion rate 1 Direct relationship ii Size smaller molecules move faster than larger molecules smaller molecule will diffuse faster 1 Inverse relationship iii Concentration gradient steeper gradient faster diffusion 1 Direct relationship 2 Concentration Gradient the difference in concentration of a substance from one area to another a Moves HIGH to LOW iv Passive transport requires no energy from the cell to make it happen v Only happens in a cell if the substance can readily cross the plasma membrane vi Water can diffuse across the cell membrane through aquaporins hydrophilic channels vii Diffusion refers to the movement of SOLUTE molecules down its OWN concentration gradient 1 Do NOT confuse this with osmosis the diffusion of WATER solution viii Osmosis diffusion of water across a selectively permeable membrane 1 Water is diffusing on its OWN concentration gradient a From a high to low concentration 2 Water diffuses across a membrane from an area of low solute concentration high water to an area of high solute concentration low water 3 WATER WILL ALWAYS FLOW TO A HIGH SOLUTE CONCENTRATION LOW WATER CONCENTRATION e Tonicity i Ability of a solution to cause a cell to gain or lose water ii Isotonic solution solute concentration is the same as that inside the cell no net water movement across the plasma membrane iii Hypertonic solution solute concentration is greater than that inside the cell cell loses water cell shrivel up iv Hypotonic solution solute concentration is less than that inside the cell cell gains water