1. Chapter 6 Energy, Enzymes, and Metabolism Biology 101 Tri-County Technical College Pendleton, SC

2. Metabolism and more… Metabolism defined as sum of all chemical reactions in a cell Anabolism is part of metabolism concerned with building up complexity in cell Requires energy to accomplish Catabolism is part of metabolism concerned with breaking down complex substances into simpler ones and releasing energy in process Reactions are often linked (coupled)

3. Thermodynamics Energy defined as ability to do work Work defined as movement of mass through space Kinetic versus potential energy In biochemistry, energy represents capacity for change First Law: energy (matter) cannot be created nor destroyed Can be converted from one form to another

4. Thermodynamics, cont. Chemical to light; mechanical to electrical; potential to kinetic; and vise versa Law applies to the universe or any closed system Open system merely one part of larger closed system Law states that in any interconversion, the total energy before and after the conversion is the SAME

5. Thermodynamics III Second law states that “in every energy conversion, some of the energy becomes unavailable to do work” Some lost to entropy (disorder)/some as heat Total energy called enthalpy (H) Usable energy (doing work) is called free energy (G) Unusable energy called entropy (S) which is multiplied by absolute temperature

6. Thermodynamics IV H = G + TS Can be rewritten to G = H – TS Energy changes measured in calories (cal) or joules (j) Change in value represented by Δ (delta) and can be negative or positive If ΔG is negative, free energy released; if positive, free energy consumed Endergonic versus exergonic reactions

7. Exo versus Ender Visual

8. Energy Coin of the Realm Adenosine triphosphate (ATP) Can be hydrolyzed and can donate a phosphate group to many different compounds ADP-ATP cycle classic example of energy coupling and biochemical reaction Couples endergonic and exergonic reactions Time for an Estesism…Hot damn!!!

9. ATP Visual

10. ADP-ATP Cycle Visual

11. …but how does it work Phosphate groups are negatively charged Lots of free energy required to overcome tendencies of phosphates to repel each other Energy invested to make ADP from AMP and ATP from ADP When phosphate removed, energy used to put it there released and used to do work Active cells requires millions of ATPs per second to drive its machinery

12. Energy Coupling Visual

13. Here and there..mostly there Catalyst is any substance that speeds up chemical reaction w/o itself being used up Most biological catalysts are proteins called enzymes Certain RNA molecules (ribozymes) TOO **Reactions would proceed eventually given infinity Not fast enough or often enough to sustain life

14. Enzymes, cont. Apoenzyme  Holoenzyme Coenzymes and cofactors For reaction to proceed, energy barrier must be overcome **Exergonic reactions proceed ONLY after they are pushed over energy barrier by small amount of added energy Needed energy called activation energy (E A )

15. Enzymes III E A changes reactants into unstable molecular forms called transition-state species Could lower E A by >ing temperature Sucrose and bunsen burner..care for a light? Enzymes work by lowering E A so reaction can proceed at temperature favorable to life Some can catalyze 400 million reactions/sec Liver enzyme catalyse

16. Activation Energy Visual

17. Enzymes and Substrates In enzyme-catalyzed reactions, reactants are called substrates Substrates bind to a particular site on enzyme called the active site Specificity of enzyme results from exact 3- dimensional shape and structure of enzyme Reason enzyme recognizes its substrate is because it “fits” Most enzyme names end in “ase”

18. Enzymes, cont. Enzyme-substrate complex  reaction Enzymes lower E A by one/more processes Orient substrates Add charges to substrates Induce strain in the substrates Competitive and noncompetitive inhibition Two models of enzyme specificity “Lock and key” and “induced fit” Induced fit most widely accepted model

19. Enzyme-Substrate Visual

20. Induced Fit Visual

21. Factors Affecting Rate No enzyme present, reaction rate would be directly proportional to [ ] of substrate Higher [ ], the more collisions=more reactions Addition of enzyme speeds up reaction and changes plot of reaction Rate >es as substrate >es but then levels off Enzyme has become saturated (working as fast as it can)

22. Factors, cont. Turnover number = number of molecules converted to product in one second If enzyme saturated, adding more substrate will NOT > reaction rate any further Most enzymes have optimal pH range Temperature affects enzyme activity Warming >es rate but only to a point; becomes too warm, enzyme begins to denature (nonfunctional) Isozymes (enzymes that catalyze same reaction but have different optimal temps) made by many organisms

23. And finally, brethren… Let’s briefly discuss negative feedback model