BIOL 1201 Section 1 Spring 2014 Membranes and membrane function Chapter 7 of the textbook Why are membranes called phospholipid bilayers o Biological membranes consist of phospholipids and proteins o Hydrophilic head and hydrophobic tail What is meant by fluid mosaic o Mosaic of proteins drifting laterally and fluid bilayer phospholipids How are membranes adjusted for different temperatures How do the relative amounts of saturated and unsaturated fats change o Membrane fluidity is adjusted by changing ratio of unsaturated fats to saturated fatty acids o Warm environment need more saturated fats to make your membrane more solid What is meant by membrane fluidity Why is this an important property o The viscosity of the lipid bilayer of a cell membrane o It preserves membrane function o Not too solid not too fluid 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 o Showed that membrane fluidity can acclimate and change o Membrane fluidity adjusted by changing the ratio of unsaturated to saturated fatty acid unsaturated o To make a membrane more fluid which class of fats should you increase o Increase saturated fats increasing membrane fluidity Transport of materials across the membrane What types of molecules can move easily across the membrane e g polar nonpolar large small o Nonpolar and small o Gases steroid hormones and water Transport Processes What is simple diffusion o Movement of molecules down concentration gradient o From regions of high concentrations to low concentration regions o Depends on molecular movement but o Does not require supplied energy o Does not employ a carrier molecule 1 What is facilitated diffusion o Passive transport process o Down concentration gradient o Depends on molecular movement o Does not require supplied energy o Employs a carrier molecule What is active transport o Against concentration gradient o Requires supplied energy ATP o Employs carrier molecule o Work must be done energy expended o E g The sodium potassium pump For which processes are carrier molecules involved o Facilitated Diffusion o Active Transport Which processes require the input of additional energy o Active Transport What is a semi permeable barrier o Only some types of molecules pass through When equilibrium is reached in diffusion net movement of molecules stop Yes o Molecules keep moving o There is no net charge in solute concentration Does movement of molecules stop Does No When solute concentrations are equal on both sides of the diffusion barrier the molecules no longer move False Active transport requires energy and employs a carrier molecule Passive transport movement down a concentration gradient and may employ a carrier molecule 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 o Freshwater bony fish teleost fish Hypertonic to freshwater More solutes in their body fluids than freshwater tend to gain water from environment o Marine bony fish teleost fish Hypotonic to seawater 2 Will lose water to their environment o Sharks and rays marine elasmobranch fishes Isotonic to seawater Accumulate up to 5 M urea o Marine invertebrates Isotonic with seawater Accumulate free amino acids to match the tonicity of seawater Have high concentrations of organic molecules instead of high concentrations of salt Freshwater teleost fish tend to gain water Marine teleost fish tend to lose water What is meant by hyper hypo and isotonic In which direction does water flow o Water will always move from hypo hyper o Hypotonic higher water potential fewer solutes dissolved lower concentration of solutes hypotonic solutions will lose water as the water moves from high to low o E g Hypotonic cell in a hypertonic environment will shrivel o Isotonic equivalent water potential equivalent number of solutes dissolved no net movement of water o Hypertonic lower water potential more solutes dissolved high concentrations of solutes hypertonic solutions will tend to gain water as the water moves from high to low o E g Hypertonic cell in a hypotonic environment will burst E g Dehydrated person Give an intravenous solution of saline Would it be a good idea to give a severely dehydrated person an IV solution of sterile water No it will be hypotonic to the blood cells and the red blood cells will lyse When solute concentrations are equal on both sides the molecules no longer move False there is no longer any net movement but there is still movement Isotonic marine invertebrates tend to neither gain nor lose water and the direction of net water movement Osmosis o The net movement of water across through a semi permeable membrane o Diffusion of water o From higher water potential lower concentration of solutes to lower water potential high concentration of solutes 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 o Water will flow to the side with the higher sugar concentration lower water potential o Side with low concentration of sugar has a high water potential so the water to the side with the higher sugar concentration and the lower water potential until the water potential has equal concentration on both sides 3 aquaporins What are o Channel proteins which facilitate water diffusion 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 o Enzymes lower the activation energy by speeding up reactions o Protein catalysts that position the reactants in a conformation more favorable for chemical reaction to occur o Not used up in a chemical reaction o Specific reactions require specific enzymes o Enzymes accelerate reactions by lowering activation energy barrier deltaG o Enzymes speed up reaction 10 8th 10 20th x faster o Do not reverse an energetically unfavorable reaction or uphill reactions deltaG is the same whether it is endergonic or exergonic is the same Circe Effect How are substrates lured into the active site o Circe Effect Odysseus Circe and the sirens
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