Chapter 6 Lipids

Chapter 6 : Lipids The Plasma membrane or cell membrane separates life from non-life It separates the cells interior from the external environment Lipids are Carbon Containing Compounds Found in Organisms Largely NONPOLAR and HYDROPHOBIC Hydrocarbons are molecules that contain only carbon and hydrogen They are hydrogen Electrons are shared equally in C-H bonds Another name for a hydrocarbon chain is an ISOPRENIOD Function as pigments, scents, hormones, vitamins Building blacks for more complex lipids Hydrocarbon Structure A fatty acid is a hydrocarbon chain bonded to a Carboxyl functional group Contain 14-20 carbon atoms Can be saturated or unsaturated Saturated One single bonds between the carbons Unsaturated One or more double bonds in the hydrocarbon chains Bend Saturated Hydrocarbon chains consist of only single bonds between the carbons Has the maximum number of hydrogen atoms Highly saturated lipids such as butter as solid at room temperature Unsaturated hydrocarbon chains have one or more double bonds in the hydrocarbons chains Hydrogen atoms are removed to make a double bond Polyunsaturated chains have many double bonds Highly unsaturated lipids are liquid at room temperature Break double bonds and hydrogen atoms Highly unsaturated lipids are liquid at room temperature Unsaturated oils may be HYDROGENATED (added hydrogens) Break double bonds and add hydrogen atoms Saturated lipids with long hydrocarbons tails such as waxes form stiff solids at room temperature (bee wax, coticule of plant cells) make really good water proof barriers. This prevents dehydration 3 types of Lipids found in cells Steroids Fats Phospholipids Steroids A family of lipids Hormones such as estrogen and testosterone Cholesterol a component of plasma membrane Distinguished by 4 ring structures Steroids differ from one another by the functional groups attached to carbons in the rings Fats Are composed of 3 fatty acids linked to glycerol Also called TRICYLGLYCEROLS or TRIGLYCERIDES When their fatty acids are polyunsaturated they are liquid and form oils The primary role of fats is to store energy Fats form by dehydration reactions between A Hydroxyl group of glycerol The carboxyl group of a fatty acid The glycerol and fatty acid molecules become joined by ESTER LINKAGES Fats are not polymers Phospholipids Are Amphipathic- meaning it has a hydrophilic end and a hydrophobic end They contain both hydrophobic and hydrophilic regions The hydrophilic Head region contains Glycerol A negatively charge phosphate group A charged or polar group The hydrophobic tail region is comprised of two nonpolar fatty acid or isoprene chains Phospholipid Bilayers When amphipathic lipids are placed in water The hydrophilic heads interact with water The Hydrophobic tails interact with each other away from the water They form Miceles Or Lipid Bilayers Two sheets of phospholipid molecules align Can form spontaneously No outside energy is required Artificial Membranes Vesicles can form from phospholipid in the lap Small bubble-like structures surrounded by phospholipids Artificial membrane bound vesicles are called LIPOSOMES Plantar bilayers are lipid bilayers constructed across a hold on a glass or plastic wall Separating two aqueous solutions Flat Used to measure PERMEABILITY or lipid Bilayers Tendency of given substances to pass through Wall down a flask to test permeability Phospholipid Bilayers have Selective permeability Many factors influence the permeability of the membrane Amount of double bonds or the saturation in the lipid Length of tail Temperature Number of cholesterol molecules in the membrane Double bonds in a hydrocarbon chain can cause a King in the hydrocarbon chain Prevents the close packing of hydrocarbon tails Reduced hydrophobic Unsaturated more fluid more permeable Membranes are must more permeable Saturated Hydrocarbons have fewer spaces and stronger hydrophobic interactions Membranes are more-dense and less permeable Cholesterol Reduces Membrane permeability Adding cholesterol to membrane increases the density of the hydrophobic section Denser less permeable Temperature affects the fluidity and permeability of membranes Phospholipids in plasma membranes move laterally within the bilayers this is called FLUIDITY Membrane fluidity decreases as temperature drops Molecules in the bilayer more slowly Hydrophobic tails pack together more tightly Decreased membranes fluidity causes decreased permeability Movement across membranes: DIFFUSION Small molecules and ions in a solution, called solutes Have thermal energy Are in constant, random motion Diffusion A concentration Gradient is created by a difference in solute concentrations When a concentration gradient exists There is a NET MOVEMENT from high to low concentration Diffusion along a concentration gradient Increases entropy Is spontaneous Second law of Thermodynamics In any cyclic process the entropy with either increase or stay the same Equilibrium occurs when the molecules or ions are randomly distributed Molecules are moving randomly But there is no NET MOVEMENT Passive Transport occurs when substances diffuse across a membrane in the absence of an outside energy source Osmosis Water moves quickly across the lipid bilayer This is a special case of diffusion Occurs across selectively permeable membrane Water moves from regions of Low Solute concentration to regions of high solute concentration This dilutes the higher concentration of solute It equalizes the concentration on both sides of the bilayer An outside solution with a higher concentration is HYPERTONIC to the inside of a cell A solution with a lower concentration is HYPOTONIC to the cell If solute concentrations are equal on the outside and inside of a cell, solutions are ISOTONIC to each other Hypertonic Water moves out of cells Cell will shrink Hypotonic Water moves into cells Cell will swell Isotonic Solution No Movement The cell size will remain the same Simple Vesicle like structures that harbor nucleic acids are called PROTOCELLS Proteins alter membrane structure and function Phospholipids provide the basic membrane structure Plasma membrane contain as much protein as phospholipid Proteins can insert into a membrane They can be AMPHIPATHIC, since their side chains can be polar, charged, or nonpolar They can fold Fluid Mosaic Model Fluid Mosaic model structure suggests Some proteins are interested in the lipid bilayer This making the membrane a fluid dynamic mosaic Ion Channels are specialized membrane proteins Forms pores or openings in a membrane Ions diffuse through Electrochemical Gradients Occur when ions build up on one side of a plasma membrane They establish both a concentration gradient and a charge gradient Ions diffuse down their electrochemical gradients NA+ and CL- supper important Channel Proteins are selective Each channel protein permits only a particular type of ions or small molecule to pass through it Aquaporin permit water to cross the plasma membrane Gated Channel open or close in response to a signal Binding of a particular molecule Change in the chare across the membrane The flow of ions and small molecules through membrane channels is carefully controlled When transmembrane proteins assist passive transport, the process is called Facilitated diffusion Facilitated diffusion can also occur though carrier proteins Change the shape to transport solutes across a membrane Transport lager molecules such as glucose Moves with the gradient Active Transport Moves substances AGAINST their gradient ATP often required Sodium Potassium Pump Pumps are membrane proteins that provide active transport of molecules across the membrane The sodium potassium pump Uses ATP Transports NA+ and CL- Secondary Active Transport Moving materials against their concentration gradients Plasma membranes define the intracellular environment 3 mechanisms of membrane transport Passive Diffusion Facilitated diffusion through channels or carriers Active Primary and secondary active transport