An Introduction to Metabolism

1. Chapter 8 An Introduction to Metabolism

2. 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

3. 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

5. 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

6. Why we are open systems

8. 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

9. 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

10. Catabolic vs. Anabolic • Catabolic: break down complex molecules into simpler compounds • Releases energy • Anabolic: build complicated molecules from simpler ones • Consumes energy

11. 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

12. 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

16. 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)

17. 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)

20. ATP synthesis • endergonic reactions of cellular respiration phosphorylate ADP-reforms ATP • ADP + Pi (PO4 = phosphate) ATP • More about this in Chapter 9

21. 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!

24. 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

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

27. 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>>>>>>>

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

30. 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?