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Chapter 6 Energy and Metabolism Energy: • The capacity to do work – any change in the state of motion or matter • Measured as heat energy • Unit is the kilocalorie (K) • Heat energy flows from an object of higher temperature to an object of lower temperature • Cells cannot use heat energy for work because they are too small for a significant temperature gradient Types of energy: • Potential energy - the capacity to do work based on position or state – Chemical energy is potential energy stored in chemical bonds – Food is a type of chemical (potential) energy • Kinetic energy – the energy of motion – Mechanical energy is kinetic energy of motion – Muscular movement is mechanical (kinetic) energy Types of energy systems: • Closed – the system does not exchange energy with its surroundings • Open – the system does exchange energy with its surroundings • Are biological systems closed or open? Why? Thermodynamics • The study of energy and its transformations • First law of thermodynamics – Energy cannot be created or destroyed – Energy can be transferred or changed in form – Organisms cannot create energy but can capture it • Second law of thermodynamics – No energy transfer is 100% efficient – Some energy is lost as heat and cannot be used to do work – Organisms fight entropy only with constant input of energy from their surroundings Metabolism • • Needed for organism’s life processes The sum of all chemical activities within an organism • Two processes: 1. Anabolism – requires energy input • Complex molecules are synthesized from simpler substances 2. Catabolism – releases energy • • Larger molecules are broken down to smaller ones In living systems catabolism usually supplies the energy needed for anabolism Types of reactions: • Exergonic – spontaneous or downhill – Releases energy that can perform work – Products have less energy than the reactants • Endergonic – nonspontaneous – Energy must be supplied from the environment – Products will have more energy than the reactants ATP: Adenosine triphosphate • Holds energy for very short periods • Releases energy when third phosphate group is removed: ATP ADP + P • Links exergonic and endergonic reactions – used for catabolism and anabolism ATP and ADP • Nucleotides: – Adenine – Ribose – Phosphate groups • ATP = three phosphates • ADP = two phosphates • Moving from ATP to ADP releases energy in an exergonic reaction Redox Reactions • OIL RIG: – Oxidation is lost; reduction is gain • Energy moves with the electrons: – The substance that becomes oxidized gives up energy (and an electron) – The substance that becomes reduced gains energy (and an electron) • Always paired in biological systems – free electrons cannot exist in nature • Redox reactions in cells generally involve the transfer of a whole hydrogen atom rather than just an electron Acceptor molecules... • NAD+ gains H atom (is reduced) to form NADH • NADH stores large amounts of energy • This energy is transferred in a series of reactions to other molecules that will eventually form ATP • NADP+ is chemically similar • Reduced to form NADPH, but this is not involved in ATP formation NAD+(oxidized) to NADH (reduced) Enzymes • Are biological catalysts • Cells need enzymes to regulate the rate of chemical reactions • These work by lowering the activation energy of a chemical reaction (energy required to break existing bonds) • Although most enzymes are proteins, some types of RNA molecules have catalytic activity as well Enzymes… • Enzyme + substrate enzyme-substrate complex • ES complex enzyme + product(s) • The enzyme is not permanently altered by the reaction and can be reused • The substrate joins to the enzyme at the active site • As the substrate joins the enzyme – it causes a shape change – induced fit • Enzymes are specific – the shape of the substrate must fit Enzymes… • Work best at specific temperature and pH conditions • Catalyze virtually every chemical reaction that takes place in an organism • Some enzymes consist only of protein • Some enzymes have two components – Protein called apoenzyme – Cofactor Control of reactions: Inhibition • Feedback inhibition: • Formation of an end product inhibits an earlier reaction in the metabolic pathway Inhibition… • Competitive inhibition – Inhibitor competes for the substrate for the active site • Noncompetitive inhibition – Inhibitor binds with enzyme at a site other than active site • Irreversible inhibition – Inhibitor combines with an enzyme and permanently inactivates it Competitive and noncompetitive inhibition