BIOL 1201 Section 1 Spring 2015 Membranes and membrane function Chapter 7 of the textbook Why are membranes called phospholipid bilayers Because a membrane is made mostly of phospholipids Hydrophobic tail and hydrophilic head fluid structure proteins embedded in What is meant by fluid mosaic Mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids How are membranes adjusted for different temperatures How do the relative amounts of saturated and unsaturated fats change Membrane fluidity is adjusted by changing ratio of unsaturated fats to saturated fatty acids Warm environment need more saturated fats to make your membrane more solid Saturated tails pack closely together which causes viscosity High temperatures less fluid less phospholipid movement What is meant by membrane fluidity Not too fluid can t support protein function Not too solid permeability changes enzymes no longer able to move within Why is this an important property Membranes must be fluid to work properly It preserves membrane function Henrique and Hanson performed experiments with pigs and examined the effects on the relative amounts of saturated and unsaturated fats What did they find One can see similar patterns comparing species with different body temperature or cells grown at different culture temperatures That membrane fluidity can acclimate to temperature pigs that were raised wearing underwear in a hotel room had subcutaneous fats with higher melting points One can see similar patterns comparing species with different body temperature of cells grown at different culture temperatures Transport of materials across the membrane 1 What types of molecules can move easily across the membrane e g polar nonpolar large small Direction down the concentration gradient high to low Nonpolar small gas steroid hormones water Transport Process What is simple diffusion Diffusion movement of molecules so that they are spread out evenly more less concentration What is facilitated diffusion What is active transport No energy required can also be considered passive transport Energy and work are required mostly supplied by ATP Carrier proteins and Transport proteins help Transport Proteins build into membrane For which processes are carrier molecules involved Which processes require the input of additional energy Active transport requires carrier molecules and also the input of energy What is a semi permeable barrier Only some types of molecules are able to move through the barrier membrane Diffusion of certain solutes across a membrane When equilibrium is reached in diffusion Does movement of molecules stop Does net movement of molecules stop Net movement stops but molecules still pass through just at even rates Tonicity and aquatic organisms In lecture we presented examples of aquatic animals from freshwater and seawater Bony fish sharks and invertebrates How do they compare to their environments Tonicity the ability of surrounding solution to cause a cell to gain or lose water Depends on the solute s concentration and membrane permeability What is meant by hyper hypo and isotonic In which direction does water flow Osmosis and the direction of net water movement 2 Be able to analyze U tube experiments involving a semipermeable barrier and solutions with different concentrations of solutes in either arm of the U tube Isotonic No net movement of water equal concentration Volume is stable Hypertonic water leaves cell higher concentration outside the cell Shriveled Hypotonic Water enters the cell lower concentrations inside Lyses Osmosis diffusion of free water across the cell s selectively permeable membrane What are aquaporins Type of channel protein transport protein that helps pass water through the membrane Figures 7 2 to 7 6 7 8 7 11 to 7 15 7 17 and 7 19 Enzymes and Energy Chapter 8 How enzymes function How do they work What aspects of the energetics do enzymes change What aspects of energetics do they not affect Enzymes lower the activation energy barrier They position the reactants so that they become more favorable for the chemical reaction to occur They can t change the delta G only deal with delta G double dagger values Circe Effect How are substrates lured into the active site Positively charged Arginine side chain lures negatively charged metabolite The Substrate then becomes the product Odysseus Circe and the sirens what are the analogs to these characters in the binding of substrates to enzymes Odysseus men negatively charged substrate Siren positively charged arginine side chain Circe active site 3 What are the interactions between substrate and the active site Weak How do temperature changes affect the rates of reactions catalyzed by enzymes What is meant by the thermostability of an enzyme Proteins can be denatured by physical factors such as temperature and pH Lower temperature lower activation rate Thermostablity able to remain stable and function at high temperatures What sets the upper temperature limit for life the presence of liquid water or the stability of biological molecules Why is there an upper limit The stability of biological molecules at high temperatures set the upper limit because proteins and DNA break down easily at high temperatures Enzyme homologs what are they Enzymes in different species catalyze the same reactions Enzyme homologs from cold and warm adapted species how do they differ in order to adapt to the different thermal energy in their environments to maintain adequate catalytic rates Cold lowers the activation energy barrier more than the enzymes of warm adapted organisms What are the differences in activation energy barriers G between the enzymes of warm and cold adapted species Cold species have lower delta G values that turn the substrates into products at a faster rate Coenzymes What is their role in metabolism Bind to an enzyme to help speed up the reaction What do we mean by reducing power Ability to reduce donate electrons Transfer the electrons and hydrogen with help from a carrier molecule There is a constant pool cycling between the reduced and oxidized forms How does oxidation affect the energy of the molecule which is oxidized Reduces energy by removing the electron or hydrogen from a molecule 4 How does reduction affect the energy of the molecule which is reduced Adds energy by the addition of an electron or hydrogen from a molecule Inhibition Competitive Noncompetitive Allosteric Feedback Competitive Substrate that competes for binding at
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