Enzymes (Chapter 8 Metabolism)

1. Enzymes (Chapter 8 Metabolism)

2. Chemical Reactions • A chemical reaction is a process that changes one set of chemicals into another set of chemicals. Reaction of sulfuric acid and sugar. The acid dehydrates the sugar forming a pillar of carbon (black) and steam.

3. A chemical reaction is a process that changes, or transforms, one set of chemicals into another. And involves changes in the chemical bonds that join atoms in compounds. The elements or compounds that enter into a chemical reaction are known as reactants. The elements or compounds produced by a chemical reaction are known as products. Reactants Products A+ B  AB AB  A + B

4. Chemical equation: • CO2+ H2O H2CO3 • This reaction enables the bloodstream to carry carbon dioxide to the lungs. • CO2 is non polar - equal sharing of electrons • H2O is polar -unequal sharing of electrons Example of Chemical reaction

5. CO2 + H2O H2CO3 • Reaction is reversible • Move in both directions at same time • Equilibrium is reached when both the reactants and products are made at the same rate Chemical Equilibrium

6. Metabolism is the sum of an organism’s chemical reactions • Metabolism is an emergent property of life that arises from interactions between molecules within the cell

7. Energy in Chemical Reactions • Energy = ability to move or change matter • In chemical reactions, energy is absorbed or released when bonds are broken and new ones formed • Activation energy = the energy needed to start a chemical reaction • Chemical “push” that starts a chemical reaction • Biological reaction (chemical reactions that happen in cells) need activation energy to begin

8. What drives reactions? • If some reactions are “downhill”, why don’t they just happen spontaneously? • because covalent bonds are stable bonds Stable polymersdon’t spontaneouslydigest into theirmonomers

9. energy Activation Energy • Breaking down large molecules requires an initial input of energy • activation energy • large biomolecules are stable • must absorb energy to break bonds Can cells use heat to break the bonds? cellulose CO2 + H2O + heat

10. Activation energy

11. Activation energy is a factor in whether the overall chemical reaction releases energy or absorbs energy. Endergonic Exergonic

12. The Activation Energy Barrier B A C D Transition state B A EA = activation energy Free energy D C Reactants B A DG < O C D Products Progress of the reaction

13. Activation energy • The amount of energy needed to destabilize the bonds of a molecule • moves the reaction over an “energy hill”

14. Reducing Activation Energy by • Catalyst • Reducing the amount of energy to start a reaction Call in the ENZYMES! G

15. Catalysts • So what’s a cell got to do to reduce activation energy? • get help! … chemical help… ENZYMES Call in the ENZYMES! G

16. Course of reaction without enzyme EA without enzyme EA with enzyme is lower Reactants Free energy Course of reaction with enzyme DG is unaffected by enzyme Products Progress of the reaction ENZYMES work by LOWERING ACTIVATION ENERGY;

17. Enzymes

18. Enzymes are Biological Catalysts • Enzymes are biological catalysts, which means they speed-up chemical reactions by reducing the activation energy needed for the reaction to occur

19. Enzymes are Biological Catalysts • facilitate chemical reactions • increase rate of reaction without being consumed • reduce activation energy • don’t change free energy (∆G) released or required • Highly specific • Most enzymes are proteins( & RNA-ribozymes) • Without enzymes, chemical reactions would not occur fast enough to sustain life.

20. substrates (reactants) enzyme Substrates bind to anenzyme at certain places called active sites. Enzyme structure is important • Shape allows only certain reactants to bind to the enzyme • Substrate • Reactant that binds to enzyme • Enzyme substrate complex temporary association • Enzyme-Substrate Complex • enzyme + substrate • Active site • Specific location where a substrate binds on an enzyme • Product • End result of reaction Substrate held in active site by WEAK interactions (ie. hydrogen and ionic bonds)

21. LOCK & KEY(simple model)Active site on enzymefits substrate exactly • INDUCED FIT(more accurate)Binding of substrate causes enzyme to change shape so active site so it fits substratemore closely • Conformation change TWO MODELS PROPOSED

22. How does it work? • Variety of mechanisms to lower activation energy & speed up reaction • active site orients substrates in correct position for reaction • enzyme brings substrate closer together • active site binds substrate & puts stress on bonds that must be broken, making it easier to separate molecules

23. Co-factors/Co-enzymes many enzymes require organic (co-enzymes: “vitamins”) or inorganic (co-factors: “minerals”) groups of atoms to be complexed with the enzyme. Ex. Many enzymes involved in interacting with DNA require zinc2+ ions as co-factors (green spheres)

24. Specificity of Enzyme • Reaction specific • each enzyme works with a specific substrate • chemical fit between active site & substrate • H bonds & ionic bonds • Enzymes named for reaction they catalyze • sucrase breaks down sucrose • proteases break down proteins • lipases break down lipids • DNA polymerase builds DNA • adds nucleotides to DNA strand • pepsin breaks down proteins (polypeptides)

25. Enzymes can only work on one type of substrate ex: Amylase only works on starch, not on other macromolecules or other carbohydrates. . An enzymes function depends on its shape!!!

26. Reusable • Not consumed in reaction • single enzyme molecule can catalyze thousands or more reactions per second • enzymes unaffected by the reaction

27. Factors Affecting Enzyme Function • Enzyme concentration • Substrate concentration • Temperature • pH • Salinity(salt [ ]) • Activators • Inhibitors catalase

28. reaction rate enzyme concentration Factors affecting enzyme function • 1. Enzyme concentration • as  enzyme =  reaction rate • more enzymes = more frequently collide with substrate • reaction rate levels off • substrate becomes limiting factor • not all enzyme molecules can find substrate

29. reaction rate substrate concentration Factors affecting enzyme function • 2. Substrate concentration • as  substrate =  reaction rate • more substrate = more frequently collide with enzyme • reaction rate levels off • all enzymes have active site engaged • enzyme is saturated • maximum rate of reaction

30. SUBSTRATE CONCENTRATION & ENZYME ACTIVITY V MAX ← Adding substrate increases activity up to a point

31. 3. Temperature Effects on rates on enzyme activity • Optimum Temperature (T°) • greatest number of molecular collisions • human enzymes = 35°- 40°C • body temp = 37°C • Heat: increase beyond optimum T° • increased energy level of molecules disrupts bonds in enzyme & between enzyme & substrate • H, ionic = weak bonds • denaturation = lose 3D shape (3° structure) • Cold: decrease T° below optimum T° • molecules move slower • decrease collisions between enzyme & substrate

32. 37°C 70°C Temperature • Different enzymes function in different organisms in different environments hot springbacteria enzyme human enzyme reaction rate temperature (158°F)

33. How do ectotherms (cold blooded) do it? Isozymes! Different enzymes with different chemical compositions and physical properties but control the same reaction

34. 4.pH • Effects on rates of enzyme activity • pH changes • Changes charges (adds or remove H+) • disrupts bonds, disrupts 3D shape • Affects 3° structure • most human enzymes = pH 6-8 • depends on localized conditions • pepsin (stomach) = pH 2-3 • trypsin (small intestines) = pH 8

35. pH and ENZYME ACTIVITYEach enzyme has an optimal pH at which it can function

37. Salinity (salt concentration) Effects on rates of enzyme activity • Protein shape (conformation • Depends on attraction of charged amino acids • salinity changes • change (inorganic ions) • Changes charges- adds or removes cations (+) & anions (–) • disrupts bonds, disrupts 3D shape • 3° structure • enzymes intolerant of extreme salinity • Dead Sea is called dead for a reason!

38. Denatured Enzymes •  a structural change in macromolecules caused by extreme conditions. • Denatured enzymes have lost their shape and can no longer bond with their substrate.

39. Increasing temperature increases the rate of an enzyme-catalyzed reaction up to a point. Above a certain temperature, activity begins to decline because the enzyme begins to denature.