Chapter 8 Objectives ○ Distinguish between the following pairs or terms: catabolic and anabolic pathways; kinetic and potential energy; open and closed systems; exergonic and endergonic reactions ○ Explain how the nature of energy transformations is guided by the two laws of thermodynamics ○ Describe how ATP functions as the universal energy shuttle in cells ○ Describe the structure of enzyme-substrate interactions and how enzymes catalyze biological reactions Introduction Characteristics of organisms are all the end-products of the chemical reactions that occur in their cells The cell is a mini factory Roughly 8.64 x 1026 reactions per day Chemical reactions carried out for the purpose of energy transformation or making necessary substances Energy-The Capacity to do Work Energy is described and measured by how it affects matter Two types of energy: kinetic-energy of motion potential-stored energy because of structure or location Example: the energy stored in chemical bonds Why we are open systems Laws of Energy Conservation Thermodynamics = study of energy transformations Two laws govern energy transformation: First law (energy conservation) ○ total amount of energy in universe is constant can be transferred or transformed but cannot be created or destroyed Second law (entropy-disorder- increases) ○ every energy transformation increases entropy energy available for doing useful work decreases with every transformation Organization of the Chemistry of Life into Metabolic Pathways Metabolism transforms matter and energy Subject to the laws of thermodynamics ○ Metabolism is the sum of an organism’s chemical reactions Metabolic pathway has many steps that begin with a specific molecule and end with a product Each step catalyzed by a specific enzyme Catabolic vs. Anabolic Catabolic: break down complex molecules into simpler compounds Releases energy Anabolic: build complicated molecules from simpler ones Consumes energy G = Gibbs Free Energy (Delta) G = Free energy available to do work in a cell A - G means a rxn gives off energy; it provides power A + G means a rxn needs energy; it will not run unless energy is first added Every rxn has a specific G Energy Relationships in Living Things Chemical reactions in cells either store or release energy endergonic reactions require input of energy ○ energy input equals difference in potential energy between reactants and products exergonic reactions release energy ○ energy released equals difference in potential energy between reactants and products cellular metabolism is sum total of all endergonic and exergonic reactions in cells Energy Relationships ATP is cell’s energy shuttle most cell reactions require small amounts of energy food storage molecules contain large amounts of energy energy in food molecules converted to energy in ATP ○ one food molecule=many ATP (e.g. 1 x glucose=36 ATP) Energy Relationships Hydrolysis of ATP releases energy Most energy is located in the covalent bond between 2nd and 3rd phosphate groups easily hydrolyzed forms ADP and phosphate group ATP ADP + Pi ( means PO4 = phosphate) ATP synthesis endergonic reactions of cellular respiration phosphorylate ADP-reforms ATP ADP + Pi (PO4 = phosphate) ATP More about this in Chapter 9 Enzymes Enzymes are large protein molecules that act as biological catalysts Energy of activation (EA) is “energy barrier”, amount of energy needed to start a reaction Enzymes can lower energy barriers = EA Enzymes cannot lower G! Enzyme Process Specific enzymes catalyze each cell reaction reactant=substrate reactant binds to enzyme active site substrate converted to product enzyme unchanged and releases product Enzymes and Denaturation Factors that affect enzyme activity temperature pH salt concentration ( ions) presence of co-factors denaturation Denaturation = disruption of the enzyme structure due to adverse conditions Example: PH to high or low These factors may lead to Question: How do you stop enzyme activity but not destroy the enzyme? Answer: Inhibition Inhibitors block enzyme action, ○ competitive inhibitors-bind to active site ○ noncompetitive inhibitors-bind to second site on enzyme ○ negative feedback-inhibition by product of reaction some pesticides and antibiotics function by inhibiting enzymes Inhibitors most often work on a temporary basis BUT>>>>>>> A+BC : G= - 8.6 kcal needs 8.6 kcal to run the reaction A. B. True False Checklist What is energy? What are the types of energy? What are the laws of thermodynamics? Catabolic vs anabolic? What is ∆G? + ∆G means what? - ∆G means what? What do these look like graphed? What are enzymes? What do they do? Do enzymes change the ∆G?