Outline. Metabolism: Energy and Enzymes. Forms of Energy. Chapter 6

Transcription

1 Metabolism: Energy and Enzymes Chapter 6 Forms of Energy Outline Laws of Thermodynamics Metabolic Reactions ATP Metabolic Pathways Energy of Activation Enzymes Photosynthesis Cellular Respiration 1 2 Forms of Energy Kinetic - Energy of motion. Mechanical Potential - Stored energy. Chemical Laws of Thermodynamics First law (law of conservation of energy) states: Energy cannot be created or destroyed, but it can be changed from one form to another. Second law states: Energy cannot be changed from one form to another without a loss of usable energy. 3 4

2 5 6 Cells and Entropy Second law can also be explained as every energy transformation makes the universe less organized and more disordered. Entropy! Second law means that every cellular process increases the total entropy of the universe. Cells and Entropy 7 8

3 Metabolic Reactions Metabolism - Sum of cellular chemical reactions. Reactants and products Free energy is the amount of energy available to perform work. Exergonic Reactions - Reactants have more free energy than products. Endergonic Reactions - Products have more free energy than reactants ATP Adenosine triphosphate (ATP) is constantly being generated from Adenosine diphosphate (ADP). Composed of adenine and ribose (adenosine) and three phosphate groups. ATP Cycle 11 12

4 Coupled Reactions Coupled Reactions In coupled reactions, the energy released by an exergonic reaction drives an endergonic reaction Function of ATP Chemical Work - Energy needed to synthesize macromolecules. Transport Work - Energy needed to pump substances across plasma membrane. Mechanical Work - Energy needed to contract muscles, beat flagella, etc. Metabolic Pathways Reactions are usually part of a series of linked reactions. Begin with a particular reactant and terminate with an end product. Enzymes are protein molecules that function as organic catalysts to speed a chemical reaction

5 Energy of Activation Energy of Activation The energy that must be added to cause molecules to react with one another is called the energy of activation. Enzymes lower energy of activation by bringing the substrates into contact with one another Enzyme-Substrate Complex Enzyme-Substrate Complex In most instances, only the active site complexes with the substrates. Active site undergoes a change in shape to accommodate the substrates.! Induced fit model 19 20

6 Enzyme Speed Generally, enzyme activity increases as substrate concentration increases. More collisions between substrate molecules and the enzyme. As temperature rises, enzyme activity increases. Warmer temperatures cause more effective collisions between enzyme and substrate Enzyme Speed If temperature rises beyond a certain point, the enzyme becomes denatured and the enzyme activity levels out. Enzymes also have an optimal ph

7 Fig. 6.9 Enzyme Concentration Cells regulate which enzymes are present and/or active. Enzyme Cofactors! Vitamins! Phosphorylation! Enzyme Inhibition " Feedback Inhibition Feedback Inhibition Feedback Inhibition Most metabolic pathways are regulated by another type of feedback inhibition. End product of the pathway binds to an allosteric site.! Binding shuts down the pathway, and no more product is produced

8 Oxidation-Reduction In redox reactions, electrons pass from one molecule to another. Oxidation is the loss of electrons. Reduction is the gain of electrons. Oxidation and reduction always take place at the same time as one molecule accepts the electrons given up by another molecule Photosynthesis Carbon dioxide + water + solar energy yields glucose and oxygen. Cellular Respiration Glucose + oxygen yields carbon dioxide + water + energy. 6 CO H 2 O + energy # C 6 H 12 O O 2 Chloroplasts capture solar energy and convert it via electron transport chain to ATP. Coenzyme active during photosynthesis. C 6 H 12 O O 2 # 6 CO H 2 O + energy Most oxidations involve a coenzyme: NAD + + 2e - + H + # NADH NADP + + 2e - + H + # NADPH 31 32

9 Electron Transport System A series of membrane-bound carriers that pass electrons from one carrier to another. High-energy electrons delivered, and lowenergy electrons leave. ATP Production Chemiosmosis: Production of ATP due to a hydrogen ion gradient across a membrane Forms of Energy Review Laws of Thermodynamics Metabolic Reactions ATP Metabolic Pathways Energy of Activation Enzymes Photosynthesis Cellular Respiration 35 36