Energy and Metabolism

1. Energy and Metabolism Chapter 8

2. Outline • Flow of Energy in Living Things • Laws of Thermodynamics • Free Energy • Activation Energy • Enzymes • Forms • Activity • ATP • Biochemical Pathways

3. Flow of Energy in Living Things • Energy - the capacity to do work • kinetic - energy of motion • potential - stored energy • Thermodynamics - changes in heat • calorie - heat required to raise the temperature of one gram of water one degree Celsius • kilocalorie = 1000 calories

4. Flow of Energy in Living Things • Oxidation - Reduction • Oxidation occurs when an atom or molecule loses an electron. • Reduction occurs when an atom or molecule gains an electron. • Redox reactions occur because every electron that is lost by an atom through oxidation is gained by some other atom through reduction.

5. Laws of Thermodynamics • First Law of Thermodynamics • Energy cannot be created or destroyed, but only change form. • During each conversion, some of the energy dissipates into the environment as heat. • Heat is defined as the measure of the random motion of molecules.

6. Laws of Thermodynamics • Second Law of Thermodynamics • The disorder (entropy) in the universe is continuously increasing. • Energy transformations proceed spontaneously to convert matter from a more ordered, less stable form, to a less ordered, more stable form.

7. Free Energy • Free energy refers to the amount of energy actually available to break and subsequently form other chemical bonds. • Gibbs’ free energy (G) • change in free energy • endergonic - any reaction that requires an input of energy • exergonic - any reaction that releases free energy

8. Activation Energy • Activation energy refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction. • catalyst - substance that lowers the activation energy • cannot violate laws of thermodynamics. • direction of a chemical reaction is determined solely by the difference in free energy between the reactants and the products

9. Activation Energy and Catalysis

10. Enzymes Are Biological Catalysts • Enzymes are proteins that carry out most catalysis in living organisms. • Unique three-dimensional shape enables an enzyme to stabilize a temporary association between substrates. • Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and can then be reused.

11. Enzymes • Most enzymes are globular proteins with one or more active sites. • Substrates bind to the enzyme at these active sites, forming an enzyme-substrate complex.

12. Enzyme Forms • A multienzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another. • subunits work in concert, providing significant advantages in catalytic efficiency • RNA catalysts “ribozymes”

13. Factors Affecting Enzyme Activity • Temperature • Rate of an enzyme-catalyzed reaction increases with temperature, but only up to an optimum temperature. • pH • Ionic interactions also hold enzymes together.

14. Factors Affecting Enzyme Activity • Inhibitors and activators • inhibitor - substance that binds to an enzyme and decreases its activity • competitive inhibitors - compete with the substrate for the same active site • noncompetitive inhibitors - bind to the enzyme in a location other than the active site • allosteric sites - specific binding sites acting as on/off switches

15. Factors Affecting Enzyme Activity • activator - substances that bind to allosteric sites and keep the enzymes in their active configurations • increase enzyme activity • cofactors - chemical components that facilitate enzyme activity • coenzyme

16. ATP • Adenosine triphosphate (ATP) is the chief energy currency of the cell. • Each molecule is a nucleotide composed of ribose, adenine, and a triphosphate group. • energy stored in the triphosphate group • cell uses ATP to drive endergonic reactions

17. Biochemical Pathways • Biochemical pathways are the organizational units of metabolism. • Metabolism is the total of all chemical reactions carried out by an organism. • anabolism - reactions that expend energy • catabolism - reactions that harvest energy

19. Regulation of Biochemical Pathways • Biochemical pathways must be coordinated and regulated to operate efficiently. • advantageous for cell to temporarily shut down biochemical pathways when their products are not needed • feedback inhibition - When the cell produces increasing quantities of a particular product, it automatically inhibits its ability to produce more.

20. Feedback Inhibition

22. Summary • Flow of Energy in Living Things • Laws of Thermodynamics • Free Energy • Activation Energy • Enzymes • Forms • Activity • ATP • Biochemical Pathways