THEORY & PRAC PLT PHYS
THEORY & PRAC PLT PHYS MEPS 316
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This 15 page Class Notes was uploaded by Haylee Bode Sr. on Wednesday October 21, 2015. The Class Notes belongs to MEPS 316 at Texas A&M University taught by Staff in Fall. Since its upload, it has received 16 views. For similar materials see /class/225892/meps-316-texas-a-m-university in Molecular Biosciences at Texas A&M University.
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Date Created: 10/21/15
Energy and Cells Chapter 2 httpwwwplantphysnet Energy transformations play a key role in all physical and chemical processes that occur in plants Energy by itself is insuf ficient to drive plant growth and develop ment Enzymes are required to ensure that rates of biochemical reactions are high enough to support life 39 l 4 g r 39 I f W 5 is R1359 Milan Phoch ulmmV The two primary energy transformations in plants are photosynthesis and respiration Plants use photosynthesis to make energyrich sugars from energypoor CO2 and water Plants use respiration to convert sugars to CO2 and water Some of the energy released during respiration is conserved in chemical bonds of other molecules such as ATP Energy and Work The First Law of Thermodynamics states that energy cannot be created or destroyed but only converted to other forms In other words you can t get something for nothing Leaves absorb energy from their surround ings Some of that energy is dissipated as heat and radiation and some is stored in the leaf By the first law Total energy absorbed energy dissipated energy stored Although the energy absorbed by the leaf has been transformed the total energy remains the same The first law dictates that the energy absorbed by leaves during photosynthesis cannot exceed the energy of the absorbed light No matter how hard you try you can t get more energy out of a plant than you put in There are no exceptions The Second Law of Thermodynamics states that all energy transformations are inefficient In other words the amount of useful energy decreases in all energy transformations Thus you cannot break even Cells derive energy from sugars and fats for growth repair and reproduction The chemical reactions that free this energy are inefficient and release heat Plants can transform energy from one form to another the can store the ener or use it for re air movement or reproduction but only temporarily Eventually all energy is trans formed into heat The second law also deals with the direction of spontaneous processes Total entropy of a system which is the amount of energy that is not available to do work always increases Low Entropy O 0 O O o o A lowentropy system has a high capacity to do work Molecules in a region where their concentration is high spontaneously move to a region where their concentration is low Low Entropy O 00 O O 0 o o A highentropy system has a low capacity to do work Work must be done to convert a highentropy system to a low entropy system High Entropy O The potential energy of a compound is con tained in its chemical bonds When these bonds break the energy that is released can be used to do work such as form other bonds The amount of energy available to do work is the free energy G of the mole cule Chemical reactions change the free energy We denote this change as AG Entropy increases with temperature so that higher temperatures speed reactions and increase disorder Spontaneous reactions exergonic reactions release heat and have a AG less than zero They form products with less free energy than their reactants Spontaneous reactions increase the entropy of the system An example of an exergonic reaction is oxidation of glucose to form CO2 and H20 CGHQO6 602 6C02 6H20 energy This reaction has a AG of 28 MJ mol39l which means that oxidation of 1 mole of glucose releases 28 MJ of energy The photosynthetic reaction is the reverse of the above reaction and requires input of energy At equilibrium AG is zero The further a reaction is from equilibrium the more work the reaction can do On the other hand work must be done to displace a system from equilibrium Because all of life s 7 rocesses re ruire work cells must remain far from equilibrium to stay alive They do this by continually pre venting accumulation of reactants of meta bolic pathways thereby reducing entropy Oxidation and Reduction A is emailed OAlGlPP Izom ulmd A Most energy transformations involve oxidation and reduction Oxidation is loss of electrons either alone or with hydrogen from a donor to an acceptor H 5 ru ncud A 5 Cxldlled B u menud Olidlzbll compound A Reduction is addition of electrons either alone or with hydrogen to a molecule Reduction reactions require a net input of energy 1 m mu d B W A x Gunmen Qumran as Hum30 Compound A compound E Oxidation and reduction occur in concert If some thing is reduced something else is oxidized Adenosine Triphosphate ATP as an Energy Source N MW When cells need energy they hydrolize ATP A large amount of energy is released when the terminal phosphate group is cleaved ATP is literally the energy currency of cells 7 AW When cells need energy they spend ATP by converting it to adenosine diphosphate ADP inorganic phosphate Pi and energy ATP H20 gtADP Pi energy AG 30 kJ mol391 J39CF MP The amount of energy released by converting ATP to ADP and Pi is about twice as much as needed to drive most cellular reactions The rest is dissipated as heat V MW Much of the energy from conversion of ATP to ADP is available to cells immediately Fats and starch store large amounts of energy but their energy must first be stored in ATP before it can be used Accomplishing all the work in a plant requires large amounts ofATP The plant doesn t run out of ATP because it is recycled quickly Conversion of ADP back to ATP via the following reaction requires input of energy ADP Pi energy gt ATP AG 30 kJ mol391 v Producl 2 Siltsnare E Cells couple the breakdown of ATPto other reactions that occur at the same time These coupled reactions drive other reactions that do work or make other molecules p r menu 2 ATP Suusuaie In this example the conversion of substrate 1 to product 1 provides energy AG reaction to produce ATP Hydrolizing ofATP releases energy to form product 2 from substrate 2 AG reaction Protons as an Energy Source STRDMA Liqu my b PQH I LN page M 1 PSII APPS yr i i i 1 I f msmqumonc if 72 quot 02 We Oxidation quot quot 7 chemich afwater potzr matl a e LUMEN Lili FWWx Protons W are another major energy currency of cells Membranes of mitochondria and chloroplasts use energy stored in proton gradients to make ATP from ADP and P 11 Energy is harvested from protons as they diffuse down a concentration gradient through ATP synthase complexes in the membranes Energy must be used to maintain the proton gradient ln chloroplasts this energy comes from light during photosynthesis ln mitochondria the energy comes from rearrangement of chemical bonds during respiration 173 ggggg x At all other membranes in the cell proton pumps HATPase hydrolyze ATP to power transport of protons out of the cytosol and establish mem brane potentials Electrochemical Potential Membrane If we have two compartments divided by a membrane and the compartments contain solutions of an un charged solute solute will diffuse from compartment 2 with the higher concentration to compartment 1 with the lower concentration increasing the entropy AG Membrane In this case AG is negative and work is done as a result of the diffusion 1 O AG Membrane o o O O 0 To move uncharged solutes from 1 to 2 requires input of energy AG is positive and work must be done to move against the concentration gradient Membrane Things become more complex if the solutes carry an electrical charge Transfer of positivelycharged particles cations from 1 to 2 causes a difference in charge to develop across the membrane Membrane To move the cations from 1 to 2 requires that work be done to overcome the electrochemical potential gradient and the concentration gradient The difference in electrical potential across the mem brane is called membrane potential
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