2. Enzymes

3. What is it?? Enzymes are PROTEIN molecules. Protein molecules are composed of one or more amino acid chains, folded into uniquely shaped globs.  Enzymes act as CATALYSTS!  Catalysts are chemicals that regulate the rate of chemical reactions.  Are not consumed or altered during the reaction

4. Activation Energy  Activation Energy is the energy input required to initiate any reaction.

5. Activation Energy  Activation Energy is the energy input required to initiate any reaction.  Enzymes regulate cell activities (metabolism) by lowering the activation energy  reactions, therefore, occur more rapidly and at lower temperatures.

6. Activation Energy

9. FUNCTION vs. SHAPE TWO THEORIES 1)LOCK & KEY THEORY Each chemical reaction requires its own enzyme therefore “one reaction = one enzyme” concept The enzyme forms a temporary bond with a special molecule called a SUBSTRATE substrate a molecule on which an enzyme works –A substrate is always… »the substance acted upon »the substance which is changing

10. Active Site the area of an enzyme that combines with the substrate

11. Get’in Together When the substrate and the enzyme combine or “join” at the active site, the tandem is called an Enzyme-Substrate Complex.

12. Lock & Key (Con’t) –The ENZYME-SUBSTRATE COMPLEX then separate into product(s) and enzyme

13. Important Note that: –The enzyme remains unchanged and ready to react again with a new substrate.

14. Important The substrate has been turned into products.

15. INDUCED FIT MODEL Improved Theory – 1973 –suggests that the shape of the active site does NOT exactly fit the shape of the substrate –The substrate forces its way into the enzyme –This makes for a tighter fit ENZYME-SUBSTRATE COMPLEX –The orientation of the substrate molecules in the ENZYME-SUBSTRATE COMPLEX helps speed up the chemical reaction by  adding stress to bonds more easily  bringing reactive sites physically closer together

16. Induced Fit (Cont’d)  Once a bond is formed (or broken) in substrate(s) then products are released and the ENZYME REMAINS UNCHANGED and may be REUSED!  A single enzyme can catalyze several million reactions in one minute  The same enzyme may also catalyze the reverse reaction  The net result is that a one step reaction is converted into a multi-step reaction, therefore, lowering the activation energy – the minimum amount of energy required to initiate a chemical reaction.

17. Naming Enzymes  Enzymes are named after the substrate which it acts upon  To name an enzyme, usually, the suffix “ase” is added to the end of the substrate name.  F or example: SubstrateEnzyme Sucrose Sucrase LactoseLactase Peptide BondsPeptidase  -Ketoglutarate...?????  -Ketoglutarase

18. Regulation of Enzyme Activity  METABOLIC PATHWAYS  cellular processes that involve many steps are controlled by enzymes  one enzyme for each step. Allosteric Activity a change in an enzyme caused by the binding of a molecule  Some enzyme’s shape may be altered by a “moderator molecule”.  can be a cofactor (mineral)  Coenzymes (organic molecules)  sometimes even the product molecule.

19. A Moderator Molecule

20. Cofactors

21. Regulation of Enzyme Activity  FEEDBACK INHIBITION  Stops a metabolic pathway  the product of an metabolic pathway acts as a moderator on an enzyme in the series, thereby altering its shape (active site)  the enzyme cannot combine with the substrate  Once the moderator molecule is removed from the moderator site, the active site snaps back to its original shape.

22. Glucose Feedback Inhibition Glucose

23. feedback inhibition feedback inhibition the inhibition of an enzyme in a metabolic pathway by the final product of that pathway

24. feedback inhibition

25. Factors Affecting Enzyme Reactions There are four factors that affect the rate at which an enzyme can work. 1) Temperature 2) pH 3) Substrate Concentration 4) Competitive Inhibitor Molecules

26. TEMPERATURE in order for a reaction to occur molecules must collide  as temperature increases, collisions increase

27. DOES RATE OF REACTION INCREASE WITH TEMPERATURE??? NOT NECESSARILY!!

28. Enzymes have an optimal temperature at which the reaction is fastest.  Beyond this temperature, the rate of reaction decreases  This is because at high temperatures, the unique shape begins to change – denaturation.  This results in a loss of the active site  Each enzyme has its own optimal temperature  Human body approx. = 37 0 C  Sperm producing enzymes = 34 0 C  This explains why fevers and colds are dangerous

30. pH  acidity or alkalinity  the lower the number the more acidic  the higher the number the more alkaline  Enzymes have an optimal pH at which the reaction is fastest  Just like with temperature, pH’s out of the optimal range will cause a decrease in rate of reaction  shape changes = enzyme denatures.

32. CONCENTRATION  Since molecules must collide for a reaction to occur, it is only logical that the more substrates you have, the greater the chance the enzyme will have of combining and reacting with it.  The rate does not continue to rise as you add more and more substrate.  There is a limit to the amount of enzyme available  A substrate cannot join with the active site of an enzyme until it is free.  Therefore, once the number of substrate molecules exceeds the number of enzyme reaction sites, the reaction rate levels off.

34. Competitive Inhibitor Molecules  Competitive Inhibitor molecules interfere with the enzyme combining with its substrate. –Competitive Inhibitor  shaped like substrate  COMPETES for active site  fits into active site  = physically blocks substrate from entering active site  enzyme becomes useless

35. Competitive Inhibition

36. Competitive Inhibitor Molecules  Examples:  Cyanide – binds to enzyme in the Electron Transport Chain preventing formation of ATP.  Carbon Monoxide – binds to hemoglobin irreversibly, therefore, no oxygen can be carried  Penicillin – binds to enzyme that allows bacteria to make its protective covering, therefore, bacteria becomes susceptible to the immune system and other drugs