1. 1 Energy and Metabolism Chapter 8

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

3. 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. 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. 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. 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. 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. 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. 9 Activation Energy and Catalysis

10. 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. 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. 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. 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. 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. 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. 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. 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

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19. 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. 20 Feedback Inhibition

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

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