Objectives INTRODUCTION TO METABOLISM. Metabolism. Catabolic Pathways. Anabolic Pathways 3/6/2011. How to Read a Chemical Equation

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1 Objectives INTRODUCTION TO METABOLISM. Chapter 8 Metabolism, Energy, and Life Explain the role of catabolic and anabolic pathways in cell metabolism Distinguish between kinetic and potential energy Distinguish between open and closed systems Explain the first and second Laws of Thermodynamics Distinguish between entropy and enthalpy Understand the Gibbs equation for free energy change Understand how usable energy changes with changes in enthalpy, entropy, and temperature Understand the usefulness of free energy How to Read a Chemical Equation A chemical reaction starts with reactants and finishes with products: C 6 H O 2 6CO 2 +6H ENERGY reactant product 6CO 2 +6H light C 6 H O 2 Disturbing either the concentration or the energy of the system alters the chemical equilibrium. Living things NEVER let their reactions go to equilibrium Metabolism The sum of all the chemical processes occurring in an organism at one time Concerned with the management of material and energy resources within the cell Catabolic pathways Anabolic pathways Catabolic Pathways Pathways that release energy by breaking down complex molecules into simpler compounds Cellular respiration C 6 H O 2 6CO 2 +6H ENERGY Anabolic Pathways Pathways that consume energy to build larger, complicated molecules from simpler ones Polymerization Photosynthesis 6CO 2 +6H light C 6 H O 2 1

2 Bioenergetics Study of how organisms manage their energy resources Energy is the capacity to do work, to move matter Kinetic energy: energy that is in motion Potential energy: stored energy based on location or structure The rearrangement of atoms in molecules may result in the potential energy of the molecule being converted into kinetic energy Kinetic energy: energy of motion; all atoms exhibit kinetic energy as all molecules are in motion Potential energy: amount of energy stored as a result of position or location Energy Laws Laws of Thermodynamics The terms open or closed systems refer to whether or not energy can be transferred between the system and its surroundings (can energy be imported or exported) First Law of Thermodynamics: Energy can neither be created nor destroyed, only transformed from one type to another Second Law of Thermodynamics: Each energy transformation results in less usable (ordered) energy Free Energy G=H-TS Free energy (G) is the portion of system energy that can do work under uniform temperature Enthalpy or work total energy is a measure of all the energy in a system Symbolically represented as H Entropy is a measure of randomness (disorder) Symbolically represented as S Temperature (T) is measured in K ΔG The higher the G the more unstable the system A change in free energy can occur with metabolism Exergonic: reactions that lose energy; -ΔG Endergonic: reactions that gain energy; + ΔG Metabolic reactions are often coupled where an exergonic reaction fuels an endergonic reaction When ΔG = 0 no work can be done When reactions go to equilibrium, ΔG = 0 (therefore metabolic reactions do not usually reach an equilibrium) Energy needed for Mechanical, Chemical, and Transport workings of the cell 2

3 Objectives Explain the role of ATP in the cell Describe ATP s composition and how it performs cellular work Explain the importance of chemical disequilibrium Understand the energy profile of a reaction including: activation energy, free energy change, & transition state Describe the role and mechanisms of enzymes Explain how enzyme activity can be controlled by environmental factors, cofactors, enzyme inhibitors, and allosteric regulators Distinguish between allosteric activation and cooperativity Explain how metabolic pathways are regulated ATP Energy molecule used to couple exergonic reactions to endergonic Nucleotide with three phosphate groups attached to the ribose sugar ATP has a high ΔG ATP Energy is released from ATP through the loss of phosphate groups Catabolic reaction resulting from hydrolysis producing ADP + P i (inorganic Phosphate) + energy (ΔG = -7.3Kcal/mol in the lab, -13Kcal/mol in the cell) How ATP works Hydrolysis of ATP produces inorganic phosphate that is attached to a molecule involved in an endergonic process Phosphorylation is the process of ATP transferring phosphate to a molecule Results in a phosphorylated intermediate that can complete the intended reaction Regeneration of ATP ATP loses energy when it phosphorylates an intermediate molecule of an endergonic reaction. ATP becomes ADP Regeneration of ATP occurs when inorganic phosphate (P i ) is bound to ADP utilizing energy supplied by a catabolic reaction 3

4 How Do We Maximize Cellular Efficiency? Use of ATP ATP is a good energy source because: It can participate in a many different kinds of reactions within the cell Usually is directly involved in reactions Little wasted energy during phosphorylation of an intermediate Use of enzymes Decrease randomness of reactions Regulation of enzymes and, thus, reactions Enzymes Proteins that assist in chemical reactions may be enzymes Specific because of conformational shape Enzymes are catalysts Catalyst: chemical that changes the rate of a reaction without being consumed Recycled (used multiple times) Enzymes reduce the activation energy of a reaction Amount of energy that must be added to get a reaction to proceed Activation Energy E A = Activation energy E A is usually supplied by heat Reactants absorb heat increasing ΔG making the reactants unstable so they react How Enzymes Work Enzymes are substrate specific Substrate: any molecule to which an enzyme will bind Although an enzyme can be a large protein, only a specific region of the enzyme interacts with the substrate Active Site: region of enzyme that reacts to substrate As enzyme and substrate bind, the enzyme shape is modified to better fit the substrate Induced fit occurs as a result of the enzyme substrate complex Enzyme Activity The rate of an enzyme catalyzed reaction is influenced by 1) concentration of the substrate or 2) enzyme concentration Some enzymes utilize 3) inorganic or 4) organic molecules as helpers Cofactor: inorganic molecule (mineral) Coenzyme: organic nonprotein molecule (vitamin) 4

5 The rate at which an enzyme can function is dependant on several physical factors including: 5) Temperature 6) ph Why? Enzyme activity Enzyme Regulation Enzyme activity may be reduced by molecules attaching to the enzyme. Inhibition may occur at two different locations competitive inhibition: inhibitor mimics molecule that attaches to active site noncompetitive inhibition at an allosteric site: inhibitor binds to enzyme away from the active site resulting in modification of active site Control of Metabolism Allosteric Regulation: enzyme function may be stimulated or inhibited by attachment of molecules to an allosteric site Feedback Inhibition: end product of metabolic pathway may serve as allosteric inhibitor Cooperativity: single substrate molecule primes multiple active sites increasing activity 5