BIO 202 Notes Lecture 8: Energy in biology, ATP Chapter 8: An Introduction to Metabolism 8.1 An organism s metabolism transforms matter and energy, subject 2 the laws of thermodynamics Metabolism: totality of an organism s chemical reactions Organization of the Chemistry of Life into <a href="/keyword/metabolic-pathways/" ><a href="/keyword/metabolic-pathway/" >metabolic pathway</a> s</a> <a href="/keyword/metabolic-pathway/" >metabolic pathway</a> : a specific molecule is altered in a series of defined steps, resulting in a certain product Each step is catalyzed by a specific enzyme Catabolic pathways: a.k.a. breakdown pathways: release energy by breaking down complex molecules to simpler compounds Cellular respiration: glucose and other organic fuels + O2 CO2 + H2O Energy becomes available to do the work of the cell Anabolic pathways: a.k.a. <a href="/keyword/biosynthetic-pathway/" >biosynthetic pathway</a> s: consume energy to build complicated molecules from simpler ones Synthesis of a protein from amino acids Catabolic and anabolic pathways can work together Energy from catabolic reactions can be stored and be used to fuel anabolic reactions Forms of Energy Energy: the capacity to cause change Kinetic energy: energy associated with the relative motion of objects Heat/thermal energy: kinetic energy associated with the random movement of atoms/molecules Potential energy: energy that matter possesses because of its location or structure Chemical energy: potential energy available for release in a chemical reaction The Laws of Energy Transformation Thermodynamics: the study of the energy transformations that occur in a collection of matter The First Law of Thermodynamics A.k.a. the principle of conservation of energy: energy can be transferred and transformed but it cannot be created or destroyed The Second Law of Thermodynamics Every energy transfer or transformation increases the entropy of the universe Or: For a process to occur spontaneously, it must increase the entropy of the universe Entropy: measure of disorder/randomness During every energy transfer or transformation, some energy becomes unusable energy In most reactions, energy converted to heat, released into surroundings 8.2 The free-energy change of a reaction tells us whether the reaction occurs spontaneously Free-Energy Change, G BIO 202 Notes Gibbs free energy, also free energy: measures the potion of a system s energy that can perform work when temp. and pressure are uniform throughout the system G = H T S Free Energy, Stability, and Equilibrium G = Gfinal state Ginitial state Free Energy and Metabolism Exergonic and Endergonic Reactions Exergonic: energy out Exergonic reaction: net release of free energy (-G, spontaneous) Endergonic: energy in Endergonic reaction: absorbs free energy from surroundings Equilibrium and Metabolism Reactions in a closed system eventually reach equilibrium Equilibrium no work For cells: death Metabolism as a whole is never at equilibrium Constant flow of materials in and out Products become reactants, waste products are expelled from the cell huge free-energy difference between glucose and oxygen at the top of the energy hill and carbon dioxide and water at the downhill end 8.3 ATP powers cellular work by coupling exergonic reactions to endergonic reactions Cells do 3 main kinds of work Mechanical Beating of cilia Contraction of muscle cells Movement of chromosomes during cellular reproduction Transport: pumping of substances across membranes against the direction of spontaneous movement Chemical: pushing of endergonic reactions which would not occur spontaneously Synthesis of polymers from monomers Cells manage their energy resources to do work with Energy coupling: use of an exergoinc process to drive an endergonic one Most energy coupling in cells driven by ATP The Structure and Hydrolysis of ATOP ATP: <a href="/keyword/adenosine-triphosphate/" >adenosine triphosphate</a> Ribose (sugar) + adenine (nitrogenous base) + chain of 3 phosphate groups Bonds between the phosphate groups can be broken by hydrolysis When the terminal phosphate bond is broken, a molecule of <a href="/keyword/inorganic-phosphate/" >inorganic phosphate</a> leaves the ATP ATP becomes ADP (adenosine diphosphate) BIO 202 Notes Exergonic Releases 7.3 kcal of energy per mole under standard conditions ATP + H2O ADP to (P)i Relatively high release of energy (relative to products) All three phosphate groups are neg charged and crowded together Mutual repulsion instability of chain If the G of an endergonic reaction is less than the amount of energy released by <a href="/keyword/atp-hydrolysis/" >atp hydrolysis</a> , then the two reactions can be coupled Overall, the coupled reactions are exergonic How ATP Performs Work The cell couples the energy of <a href="/keyword/atp-hydrolysis/" >atp hydrolysis</a> directly to endergonic processes with the help of specific enzymes A phosphate group from ATP is transferred to some other molecule, like the reactant Recipient of the phosphate group: phosphorylated intermediate More reactive than the original unphosphorylated molecule i.e. synthesis of the amino acid glutamine from <a href="/keyword/glutamic-acid/" >glutamic acid</a> and ammonia ATP phosphoryates <a href="/keyword/glutamic-acid/" >glutamic acid</a> (Glu) Ammonica displaces the phosphate group Glutamine (Glu-NH2) is formed Overall process is exergonic, so occurs spontaneously The Regeneration of ATP Regenerated by the addition of phosphate to ADP Energy required to phosphorylate ADP comes from catabolism ATP cycle: coupled exergonic and endergonic processes