Chapter 6: Energy and Metabolism

1. Chapter 6: Energy and Metabolism

2. Biological Work Requires Energy • Remember to study the terms • Energy Concepts Video

3. Fig. 8-2 A diver has more potential energy on the platform than in the water. Diving converts potential energy to kinetic energy. Climbing up converts the kinetic energy of muscle movement to potential energy. A diver has less potential energy in the water than on the platform.

4. 2 Laws of Thermodynamics • 1.) Energy cannot be created or destroyed, but it can be transferred or changed from 1 form to another • Photosynthesis: • Sun’s energy  chemical energy in bonds of carbs • Later • Chemical energy  cellular work OR mechanical energy

5. 2.) energy is converted from 1 from to another; some usable energy is converted to heat (disperses into surroundings) • SO – total amount of energy available to do work is decreasing over time • Total amount of energy overall remains constant

6. Fig. 8-3 Heat CO2 + Chemical energy H2O (a) First law of thermodynamics (b) Second law of thermodynamics

7. Entropy • Measure of disorder or randomness • Less-usable energy is more disorganized • Organized = low entropy • Disorganized = high entropy • Ex: heat • Entropy – continuously increasing in universe in all natural processes • As more heat is released, our universe becomes more disorganized

8. Enthalpy • Total potential energy of the system

9. Free Energy • Amount of energy available to do work under the conditions of a biochemical reaction

10. H = G + TS • H = enthalpy • G = free energy • T = absolute temperature in K • S = entropy • Can’t effectively measure total free energy but can measure CHANGES, so ΔG = ΔH - TΔS

11. Reactions • Exergonic – release energy HL • Endergonic – gain energy from surroundings • Activation energy – needed to start a reaction • Coupled reaction – endergonic + exergonic • exergonic reaction provides energy required to drive endergonic reaction

12. Fig. 8-6 Reactants Amount of energy released (∆G < 0) Energy Free energy Products Progress of the reaction (a) Exergonic reaction: energy released Products Amount of energy required (∆G > 0) Energy Free energy Reactants Progress of the reaction (b) Endergonic reaction: energy required

13. Enzymes – How Enzymes Work Video • Enzyme – protein catalyst • Lower activation energy • Catalyst • Speed up reaction • Substrate – substance that enzyme acts on • Enzyme-Substrate complex – • Enzymes orders structure of substrate • Gets reaction going • When breaks  product + original enzyme

14. Enzymes • Active site – on enzyme, where substrate binds • Induced Fit – substrate binds, changes shape of enzyme • Enzyme and substrate not exactly complementary

15. Fig. 8-17 Substrates enter active site; enzyme changes shape such that its active site enfolds the substrates (induced fit). 1 2 Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates Enzyme-substrate complex Active site can lower EA and speed up a reaction. 3 6 Active site is available for two new substrate molecules. Enzyme 5 4 Substrates are converted to products. Products are released. Products

16. Enzymes • Some – all protein • Some – 2 parts – work together to function • 1) protein = apoenzyme • 2) chemical component = cofactor ( C or no C) • Coenzyme – C, nonpolypeptide • Binds to apoenzyme as cofactor

17. Enzymes are most Effective At Certain Conditions • Temperature • Most – temp increases, reaction rate increases • Low temp = slow • Too high temp. – denatures enzymes • pH – enzyme active in narrow range • Charge – affect ionic bonds for tertiary and quaternary structure

18. Fig. 8-18 Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Rate of reaction 40 0 60 100 20 80 Temperature (ºC) (a) Optimal temperature for two enzymes Optimal pH for trypsin (intestinal enzyme) Optimal pH for pepsin (stomach enzyme) Rate of reaction 4 5 6 7 8 9 10 0 1 2 3 pH (b) Optimal pH for two enzymes

19. Concentrations of Enzyme and Substrate • Lots substrate – enzyme concentration limits • Less substrate than enzyme – substrate concentration limits

20. Enzyme Activity • Feedback Inhibition • Formation of a product inhibits an earlier reaction in the sequence of reactions • A  B  C  D  E • When E is low – sequence proceeds rapidly • E is high – E1 slows and can stop entire sequence

21. Fig. 8-UN1 Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Product Starting molecule

22. Allosteric Regulation • Substance binds to enzyme’s allosteric site, changing shape of active site and modifying enzyme’s activity • Allosteric site = receptor site on enzyme, not active site • Allosteric regulators – affect enzyme activity by binding to allosteric sites • Keep inactive • activate

23. Fig. 8-20 Active site (one of four) Allosteric enyzme with four subunits Regulatory site (one of four) Activator Active form Stabilized active form Oscillation Non- functional active site Inhibitor Inactive form Stabilized inactive form (a) Allosteric activators and inhibitors Substrate Stabilized active form Inactive form (b) Cooperativity: another type of allosteric activation

24. Enzyme Inhibition – can be inhibited or destroyed by certain chemicals • Reversible Inhibition – inhibitor forms weak chemical bonds w/ enzyme • Competitive – inhibitor competes w/ normal substrate for active site • No permanent damage • Noncompetitive – inhibitor binds w/ enzyme but not at active site • e enzymes by altering shape

25. Fig. 8-19 Substrate Active site Competitive inhibitor Enzyme Noncompetitive inhibitor (c) Noncompetitive inhibition (b) Competitive inhibition (a) Normal binding

26. Irreversible Inhibition – inhibitor permanently inactivates or destroys an enzyme when it combines w/ enzyme at active site or elsewhere • Ex: poison • Mercury, lead, nerve gas, cyanide