Unit 2 The problem a cell and its environment o The interior of a cell is different than its environment o How to defend the internal environment but still communicate with the external environment Transport materials across the barrier Integral membrane proteins o Amphipathic Hydrophobic nonpolar regions Hydrophilic polar regions An optimal intermediate o Not too solid o Not too fluid o Preserves membrane function o At the cell body temperature Similar fluidity in different species Species with a body temperature of 10 C will have fluidity similar to a species with a body temperature of 20 C o Do not take fluidity too literally Henrique and Hansen o 1901 o Raised pigs wearing underwear in a hot room o Changes the properties of the subcutaneous fats Had a higher melting point o Membrane fluidity can acclimate change o Membrane fluidity adjusted by changing the ratio of unsaturated to Move down the concentration gradient from high to low saturated fatty acids o Fluid membrane is unorganized looking o Not fluid will look much more organized Increase unsaturated fats o Increases the fluidity of the membrane Direction of movement o Expect Transport process o Active Against concentration gradient Requires supplied energy ATP Carrier molecule Work must be done Expend energy o Passive Down concentration gradient Does not require supplied energy Simple diffusion Depends on molecular movement Does not use a carrier molecule Facilitated diffusion Down concentration gradient Depends on molecular movement Does not require supplied energy Employs a carrier molecule When concentrations on both sides of a barrier are equal o Molecules keep moving o There is no net change in solute concentration Semi permeable barrier o Only some types of molecules pass through Diffusion o Movement of molecules down concentration gradient o From regions of high concentration to low concentration regions o Physical property of matter o Individual molecules move randomly but the effect is non random o Osmosis The diffusion of water Net movement of water across through a semipermeable membrane o From higher fewer solutes to lower concentration more solutes Movement of water across a membrane o From high to low water potential Create free energy gradient these can be used to do work o Greater free energy where there are more molecules Membrane permeability o Size and shape of molecules o Solubility in lipids o Net electric charge o Other chemical properties o Water always freely permeable Aquaporins Problems confronting organisms the membrane o Water stress Hypertonic o Lower water potential o More solutes dissolved o Hypertonic solutions will tend to gain water Channel protein which facilitate water diffusion through Hypotonic Isotonic o Higher water potential o Fewer solutes o Hypotonic will tend to lose water o Equivalent water potential o Equivalent number of solutes dissolved o No net movement Dehydrated person o Given an intravenous solution o When solute concentrations are equal on both sides the diffusion barrier of molecules still move Marine invertebrates o Isotonic with sea water o Accumulate free amino acids to match the tonicity of seawater Marine elasmobranch fishes o Sharks and rays o Isotonic with seawater o Accumulate up to 5 ures Freshwater bony fish teleost fish o Hypertonic to freshwater gain water Marine bony fish o Hypotonic to seawater Isotonic marine vertebrae o Neither can gain or lose water Freshwater teleost gain water Marine teleost fish tend to lose water Endocytosis o Moving material into the cell o Cell engulfs object becomes membrane bound vesicle o Phagocytosis For large objects o Pinocytosis o Receptor For small objects Mediated endocytosis Exocytosis Metabolism o Biological chemical reactions Chemical Reactions o Membrane bound vesicles fuse with cell membrane and expel o Occur anytime two or more atoms ions or molecules collide in such a way that they produce a new substance o Endergonic Non spontaneous Require net energy of input to proceed o Exergonic Spontaneous How are cells able to organize control o Necessary to sustain life o They are all highly organized o Cells organize and control through enzymes Metabolic transformations o Chemical transformations o Small steps o Controlled processes o Each step controlled by a protein catalyses Regulated by enzymes o These reactions will involve energy carrier molecules o Enzymes are protein catalysts Not used up in chemical reactions Enzymes are specific for specific reactions o Function by lowering activation energy barrier speeding up chemical reactions to 10 8 10 20 times what you see in the catalyst o Enzymes don t reverse energetically unfavorable reactions Free energy o Energy that is free and available to do work Gibbs free energy and chemical reactions o Spontaneous Releases Gibbs energy Exergonic o Non spontaneous Requires Gibbs energy Endergonic Energy o Potential o Kinetic First Law of Thermodynamics constant Second Law of Thermodynamics o Within any closed system the total amount of energy remains o All spontaneous processes result in an increase in randomness and disorder in the universe o And consequently in a loss of localized concentrations of energy o Entropy is increasing o You must define the system o A closed isolated system The earth is not a closed system Input of energy from the sun Require net input of energy Energy is released from the reaction Chemical reactions o Endergonic o Exergonic Delta G H T S o G o H o T o S Free energy change Enthalpy change Temperature degrees Kelvin Entropy change Burning of coal o Exergonic Exothermic o Coal and oxygen Reactants o H20 and CO2 o The activation energy barrier o Transition state o Delta G double dagger so the reaction can occur o Transition state Enzymes accelerate chemical reactions Energy required for the favorable positioning of the reactants o Reaction rates are increased because enzymes lower the activation energy barrier o Enzymes can t reverse energetically unfavorable reactions o The activation energy barrier is lowered because the enzyme positions the reactants in a conformation more favorable for the chemical reaction to occur Activation energy o Delta G double dagger o Energy necessary for reaction to occur Temperature Some organisms have low body temperatures o Low temperature o Measure of the average kinetic energy of the molecules of a substance Low energy associated with molecules o Fewer molecules have energy greater than the activation energy How
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