An Introduction to Metabolism Chapter 8

n n Objectives F F Explain how the nature of energy transformations is guided by the two laws of thermodynamics F F Distinguish between endergonic and exergonic reactions F F Describe how ATP functions as the universal energy shuttle in cells F F Describe the structure of enzyme-substrate interactions and how enzymes catalyze biological reactions

Introduction n n Characteristics of organisms are all the end- products of the chemical reactions that occur in their cells n n Chemical reactions carried out for the purpose of energy transformation or making necessary substances

Energy-The Capacity to do Work n n Energy is described and measured by how it affects matter n n Two types of energy: u u kinetic-energy of motion u u potential-stored energy because of structure or location u u Example: the energy stored in chemical bonds

 G = Gibbs Free Energy n  (Delta) G = Free energy available to do work in a cell n A -  G means a rxn gives off energy; it provides power n A +  G means a rxn needs energy; it will not run unless energy is first added n Every rxn has a specific  G n  G Never changes!

Laws of Energy Conservation n n Thermodynamics = study of energy transformations Two laws govern energy transformation: u u First law (energy conservation) F F total amount of energy in universe is constant can be transferred or transformed but cannot be created or destroyed u u Second law (entropy-disorder- increases) F F every energy transformation increases entropy energy available for doing useful work decreases with every transformation

Energy Relationships in Living Things n n Chemical reactions in cells either store or release energy u u endergonic reactions require input of energy F F energy input equals difference in potential energy between reactants and products exergonic reactions release energy F F energy released equals difference in potential energy between reactants and products u u cellular metabolism is sum total of all endergonic and exergonic reactions in cells

Energy Relationships n n ATP is cell’s energy shuttle u u most cell reactions require small amounts of energy u u food storage molecules contain large amounts of energy u u energy in food molecules converted to energy in ATP F F one food molecule=many ATP (e.g. 1 x glucose=36 ATP)

Energy Relationships n n Hydrolysis of ATP releases energy u u Most energy is located in the covalent bond between 2 nd and 3 rd phosphate groups u u easily hydrolyzed u u forms ADP and phosphate group u u ATP  ADP + P i ( means PO 4 = phosphate)

u u phosphate group used to phosphorylate cell chemicals-energizing reactions u u So ATP provides power in your cells

ATP synthesis n n endergonic reactions of cellular respiration phosphorylate ADP-reforms ATP n n ADP + P i (PO 4 = phosphate)  ATP n n More about this in Chapter 9

Enzymes n n Enzymes are large protein molecules that act as biological catalysts n n Energy of activation (E A ) is “energy barrier”, amount of energy needed to start a reaction n n Enzymes can lower energy barriers = E A n n Enzymes cannot lower  G!

Enzyme Process n n Specific enzymes catalyze each cell reaction u u reactant=substrate u u reactant binds to enzyme active site u u substrate converted to product u u enzyme unchanged and releases product

Enzymes and Denaturation n n Factors that affect enzyme activity u u temperature u u pH u u salt concentration ( ions) u u presence of co-factors u u These factors may lead to denaturation u u Denaturation = disruption of the enzyme structure due to adverse conditions u u Example: PH to high or low

Question: How do you stop enzyme activity but not destroy the enzyme? Answer: Inhibition u u Inhibitors block enzyme action, F F competitive inhibitors-bind to active site F F noncompetitive inhibitors-bind to second site on enzyme F F negative feedback-inhibition by product of reaction u u some pesticides and antibiotics function by inhibiting enzymes u u Inhibitors most often work on a temporary basis u u BUT>>>>>>>

A+B  C :  G= kcal needs 8.6 kcal to run the reaction A. True B. False