Understanding Metabolism: Forms of Energy, Laws of Thermodynamics, & Role of ATP

1. Chapter 8 An Introduction to Metabolism

2. Remember These! • Identify forms of energy and energy transformations. • Recognizes the laws of thermodynamics • Recognize that organize live at the expense of free energy • Relate Free-energy to metabolism • Identify exergonic and endergonic reactions. Define catabolism and anabolism and relate them to metabolism • Explain the structure and hydrolysis of ATP • Recognize how ATP works and is coupled to metabolism • Recognize how ATP is regenerated

3. Metabolism • Metabolism: • The totality of an organism’s chemical processes • From food to energy. • Concerned with managing the material and energy resources of a cell

4. Metabolism • Organization of living life into Metabolic Pathways.

5. Catabolism vs. Anabolism • Catabolic Pathways: • Release energy by breaking down complex molecules to simpler ones • Example: cellular respiration • Anabolic Pathways: • Consume energy to build complicated molecules from simpler ones • Example: Synthesis of a protein from AAs

6. Bioenergetics • Bioenergetics: • The study of how organisms manage their energy resources • Energy = the capacity to do work • Kinetic energy: the energy of motion • Potential energy: stored energy

7. Laws of Thermodynamics • 1st Law of Thermodynamics: • Energy can be transferred and transformed, but it can be neither created nor destroyed. • 2nd Law of Thermodynamics: • Every energy transfer or transformation increases the entropy of the universe.

8. Energy • Spontaneous process: • A change that can occur without outside help • Free energy: • The portion of a system’s energy that can perform work when temperature is uniform throughout the system, as in a living cell • Called “free” because it is available to do work

9. Exergonic vs. Endergonic Reactions • Exergonic Reactions • Proceed with a net release of free energy • “downhill” • Occur spontaneously • Example: cellular respiration • Endergonic Reactions • Reactions that absorb free energy from their surroundings • “uphill” • Do NOT occur spontaneously • Example: photosynthesis

10. Exergonic vs. Endergonic Reactions

11. ATP • All cellular work requires ATP! • Triphosphate tail is unstable • 3 phosphate groups attached to the ribose • Bonds between phosphate groups are unstable and are broken by hydrolysis • ADP + P is more stable than ATP • Therefore, this is a downhill (exergonic) reaction! • ATP has to be regenerated… • Cellular respiration!

12. ATP

13. Enzymes • Enzymes • Catalytic proteins • Catalyst = a chemical agent that changes the rate of a reaction without being consumed by the reaction

14. Enzymes • Activation Energy • The energy required to break the bonds in the reactant molecules • Heat helps… but cannot be used in cells • Why not? • Enzymes can only speed up reactions that would eventually occur anyways

15. Selectivity of Enzymes • Enzymes are VERY selective • Substrate = the reactant an enzyme acts on • Enzyme binds to the substrate(s) and converts the substrate(s) to the product(s) • Enzymes can distinguish its substrate from closely related compounds so each type of enzyme catalyzes a particular reaction

16. Enzyme Structure • Active site: • The part of the enzyme that actually binds to the substrate • Induced Fit: • As a substrate enters the active site, it induces the enzyme to change its shape slightly so that the active site fits even more snugly around the substrate

17. Enzymes

18. Enzymes • How they speed up a reaction… • Put 2 substrates together (blind date) • Create a microenvironment conducive to a particular reaction (ie. Low pH)

19. Enzyme Rate of Reaction • Rate of Reaction: • Partly a function of the initial concentration of a substrate • More substrate = more frequently access active sites of enzyme • There is a limit to this… • Sometimes all enzymes are “busy” • Enzyme is said to be “saturated” • Every enzyme has an optimal temperature and pH level

20. Enzymes • Cofactors: • Nonprotein helpers required along with enzymes for catalytic activity • zinc, iron, copper, vitamins, etc.

21. Enzymes • Enzyme Inhibitors: • Certain chemicals selectively inhibit the action of specific enzymes • Competitive inhibitors: • Mimics that compete with normal substrate molecules for admission into the active site • Noncompetitive inhibitors: • Impede enzymatic reactions by binding to a part of the enzyme away from the active site, thereby making the enzyme change its shape

22. Enzymes • Allosteric site: • A specific receptor site on some part of the enzyme molecule remote from the active site to which the molecules that naturally regulate enzyme activity bind • Act as valves that control rates of key reactions in metabolic pathways • On/Off switch

23. Enzymes • Cooperativity • One substrate molecule primes an enzyme to accept additional substrate molecules • Favorable conformational change in one subunit of an enzyme changes all the others too

24. Enzymes • Feedback Inhibition: • A metabolic pathway is switched off by its end product, which acts as an inhibitor of an enzyme within the pathway • Thermostat