BIOL 3510 1st Edition Exam 2 Study Guide Lectures 9 14 Lecture 9 September 25 Cell membranes are selective barriers that are made of lipids and proteins Lipids are a class of molecules that are insoluble in water Examples include fatty acids triacylglycerols steroids and phospholipids Lipids are often amphipathic have both hydrophobic and hydrophilic regions Fatty acids have two chemically distinct regions the carboxylic acid and hydrocarbon chain Oils and fats triacylglycerols store energy and are formed by dehydration synthesis The basic steroid skeleton is 4 linked carbon rings Phospholipids are the most common type of cell membrane lipid Phosphatidylcholine is the most common phospholipid Phospholipids form bilayers and assemble into self sealing containers Phospholipids move within one face of a bilayer but do not flip flop spontaneously Determinants of membrane fluidity are temperature and phospholipid characteristics hydrocarbon tail length shorter tails are less interactive more fluid number of double bonds in the tail saturated tails are less fluid unsaturated tails are more fluid Maintenance of membrane fluidity includes 1 Yeast and bacteria alter tail length and saturation in response to temperature changes 2 Animals cholesterol stiffens the membrane Lipds are created on the cytosolic surface of the ER scramblase and flippases are enzymes that transfer phospholipids from one membrane face to another The cytosolic face of a membrane is constant during transport Lipid bi layers are asymmetric Lecture 10 September 30 Transmembrane proteins cross membranes with alpha helices or B barrels Membranes are disrupted by amphipathic detergents Plasma membrane is supported by the cell cortex Proteins can be confined to membrane domains The carbohydrate layer coats and protects the surface of the cell It is also involved in cell cell recognition Ion concentrations differ inside and outside of a cell Charges need to balance inside and outside of the cell Lipid bilayers are permeable to 1 Non polar molecules 2 Small uncharged polar molecules Impermeable to 1 Ions 2 Large uncharged polar molecules Two types of membrane transport proteins are transporters which move molecules that bind to a binding site and channel proteins which are molecules with the right size or charge that can move through the protein The concentration gradient of a solute determines if its movement across the membrane requires active or passive transport The movement of charged molecules is controlled by the electrochemical gradient An example of passive transport is a glucose transporter Three types of active transport 1 ATP driven pump 2 Coupled pump 3 Light driven pump An example of an ATP driven pump is a Na K pump or a Ca2 pump Two types of coupled pumps participate in coupled transport such as glucose Na symport Transferring glucose across the epithelial cell layer of the gut requires active and passive transport An example of a light driven pump is Bacteriorhodopsin Lecture 11 October 2 Ion channels allow the passage of molecules via passive transport but they are not open pores Selective particular channels allow for the passage of specific ions Often gated channels open and close in response to a stimulus Membrane potential is the accumulation of electric charge across a membrane The membrane potential of a resting animal cell is negative K leak channels K flows out of the cell down its conc gradient K flows into the cells down its voltage gradient Equilibrium gives a slightly negative charge Patch clamp recording detects ion flow across a small area of membrane Also indicates that ion channels randomly switch between open and closed conformations Under various conditions one slate open or closed is favored over the other Three main types of gated ion channels voltage gated ligand gated and mechanically gated Voltage and ligand gated ion channels for example could be neuron action potentials An action potential is the propogation of an electrical signal change in membrane potential within a neuron An action potential is triggered by a depolarization of a neuron s membrane Voltage gated Na channels open and close in response to changes in membrane potential Depolarization is when a membrane potential moves towards a positive value Voltage gated Na channels have three conformations Diffusion of Na ions propagates the action potential along the axon After the Na ions rush in 1 Voltage gated K ion channels also open 2 Exit of K ions returns the membrane potential to its resting state 3 Na K pumps return the ion gradient to normal Electrical signals are converted to chemical signals and vice versa at synapses Chemical signals neurotransmitters Action potentials open Ca2 channels prompting release of neurotransmitters into the synapse Neurotransmitter binding opens transmitter gated ion channels initiating membrane depolarization They can be excitatory or inhibitory They combine interpret and record signals An example of mechanically gated ion channels are the ion channels in the inner ear Vibrations linked stereocilia move and ion channels open Lecture 12 October 7 Cells use energy stored in the bonds of sugars and fats to generate ATP Energy released during catabolism was acquired from the sun during photosynthesis Sugars monosaccharides store energy and are subunits of polysaccharides They contain carbon hydrogen and oxygen in the ratio of 1 2 1 like glucose Disaccharides and polysaccharides are formed by condensation reactions like sucrose a short term energy storage The uniting bond is called a glycosidic bond Examples of polysaccharides Starch and glycogen energy storage and Cellulose and chitin structural support Long term storage in animals fatty acids are stored as triglycerols in fat droplets in adipose cells Short term storage in animals sugars are stored as glycogen Energy storage in plants fats and starches are stored in chloroplasts If delta G 0 spontaneous exergonic energy released If delta G 0 equilibrium If delta G 0 nonspontaneous endergonic energy required During the stepwise oxidation of sugar the released energy is stored in activated carrier molecules Activated carriers are generated by coupled reactions Metabolism the chemical reactions of biomolecules It is the biochemical basis of life processes Catabolism the breakdown of larger molecules into smaller ones an oxidative process that releases energy Anabolism the synthesis of larger molecules from smaller ones a reductive process that