A.P. Biology

1. Energy and EnzymesHow do the right chemical reactions happen in the right place at the right time? A.P. Biology

2. Energy • Metabolism - All the chemical reactions in a cell • Catabolism – breaking reactions • Anabolism – making reactions • All chemical reactions need energy • Energy – the ability to do work • Muscle contraction, chemical reactions, intracellular transport, active transport

3. Types of Energy • Kinetic • Free Energy – energy available to do work • Potential • Chemical Energy – energy stored in organic molecules

4. Laws of Thermodynamics • Law of Conservation of Energy • Energy is never created or destroyed • Living things need an energy source • Law of Entropy • Energy transfer makes the universe more disordered • As energy is transferred from chemical to free energy – a lot is lost as heat • Living things need to use a lot of energy to stay ordered

5. Free Energy – energy available to do work • G(free/usable energy) = H (total energy) – TS (entropy) • Energy converted to heat isn’t available to do work. • Exergonic – catabolic – breaking – energy releasing • Endergonic – anabolic – making – energy absorbing – energy is now stored in the molecules made

6. Coupling • Energy from exergonic reactions are used to power endergonic reactions • Breaking carbs is exergonic – used to make ATP – endergonic (energy stored in ATP) • ATP is broken down to power chemical reactions, muscle contractions, etc. – exothermic • A cell can make 10 million ATP/sec.

7. Enzymes • Enzymes lower the activation energy for a chemical reaction so it can happen with less energy • One enzyme can convert 1000 molecules/sec. • Enzymes control what chemical reactions happen where and how fast in the body so they generally run the body.

10. Enzymatic Anabolic Reactions

11. Enzymatic Catabolic Reaction

12. Possible Ways Enzymes Lower The Activation Energy of a Chemical Reaction • Bring substrates together and squeezes them (takes less energy to form a bond) - anabolic • Substrate binds – changes shape of the enzyme – enzyme squeezes substrate straining the bonds (need less energy to break bonds) - catabolic • pH of active site may be highly acidic due to the R groups there (helps break bonds) - catabolic • Enzyme may actually bond to substrate causing shape changes in the substrate which makes it easier to break the bonds in the substrate

13. Things that Effect Enzyme Rate of Reaction • Temperature • At low temperatures, enzymes and substrates move slower – less collisions – slower reaction • As temperature increases – more collisions – faster rate of reaction until the temp. is too high and the enzyme denatures – rate drops to 0 • pH • All enzymes work best at an optimal pH, if that pH changes in either direction, enzymes denature

14. Things that Effect Enzymatic Rates • Enzyme concentration (amt./vol.) • Higher the concentration, faster the rate of reaction • but even starting with excess substrate, the substrate will run out as enzyme conc. increases the rate will level off • Substrate Concentration • As sub. conc. increases, act. increases • Levels off as eventually every enzyme is busy and it can’t go any faster

15. Things that Effect… • Presence of Inhibitors • Competitive • Non-competitive (allosteric) • Lab and Artificial Uses of Inhibitors • Poisons • Drugs that interfer with enzymes in pathogens (antibiotics)

16. How the body manipulates enzymes to control chemical reactions • Keep a steady amount of Product • Feedback Inhibition • the product of a multi-step pathway allosterically inhibits an earlier step in the pathway • Substrates turn enzymes on by allosteric activation and products turn off enzymes by allosteric inhibition – (Example: ATP and ADP on a glycolysis enzyme)

18. How the body manipulates enzymes to control chemical reactions • Optimize Reactions that must happen efficiently all the time • Spatial Control – some enzymes are embedded in a membrane and cannot move relative to other enzymes – therefore enzymes involved in a step-wise reaction can happen quickly and in order • Compartmentalization - some enzymes are kept in small inside an organelle where reactions can happen more quickly • Can also include keeping the pH and temperature optimal

19. How the body optimizes reactions continued • Cooperativity • used only in multi-subunit enzymes • binding of a substrate causes a conformational change in the enzyme (induced fit) that allows other substrates to bind faster • more substrate present – faster the enzyme works • Maximizes reaction with a small amount of substrate • Coenzymes and Cofactors – necessary in many cases to make the active site the right shape for the substrate • Coenzymes – organic – usually vitamins • Cofactors – inorganic such as Mg, Zn, etc. • Enzymes can be controlled by the availability of coenyzmes and cofactors

20. How the body manipulates enzymes to control chemical reactions • Make the Product Only When Needed • Protein Synthesis – If don’t want to waste energy making enzymes not needed and when needed - not needed fast – can make them from scratch • The presence of certain substrates can turn on protein synthesis or products can shut down protein synthesis at the DNA level • A messenger can signal the cell to make enzymes • Compartmentalization- Some enzymes are sequestered and released only at certain times (example amylase and pepsin)

21. Make the Product Only When Needed • Cleavage of Enzyme – enzymes are formed in an inactive form and then cleaved when needed to make the right shape (thrombin, pepsin) • Phosphorylation – adding phosphates to change the shape and activate or inactivate enzymes • pH –is varied in some organs to control enzyme action – make it the right pH to activate enzymes and the wrong pH to inactivate them (stomach and small intestine)