1 Energy and Metabolism Chapter 8

2 Outline Flow of Energy in Living Things Laws of Thermodynamics Free Energy Activation Energy Enzymes – Forms – Activity ATP Biochemical Pathways

3 Flow of Energy in Living Things Energy - the capacity to do work – kinetic - energy of motion – potential - stored energy Thermodynamics - changes in heat – calorie - heat required to raise the temperature of one gram of water one degree Celsius  kilocalorie = 1000 calories Potential energy Kinetic energy

4 Flow of Energy in Living Things Oxidation - Reduction – Oxidation occurs when an atom or molecule loses an electron. – Reduction occurs when an atom or molecule gains an electron.  Redox reactions occur because every electron that is lost by an atom through oxidation is gained by some other atom through reduction. Gain of electron (reduction) Low energy e–e– AB High energy Loss of electron (oxidation) A oo B + – A* B*

5 Laws of Thermodynamics First Law of Thermodynamics – Energy cannot be created or destroyed, but only change form.  During each conversion, some of the energy dissipates into the environment as heat.  Heat is defined as the measure of the random motion of molecules.

6 Laws of Thermodynamics Second Law of Thermodynamics – The disorder (entropy) in the universe is continuously increasing.  Energy transformations proceed spontaneously to convert matter from a more ordered, less stable form, to a less ordered, more stable form.

7 Free Energy Free energy refers to the amount of energy actually available to break and subsequently form other chemical bonds. – Gibbs’ free energy (G)  change in free energy  endergonic - any reaction that requires an input of energy  exergonic - any reaction that releases free energy Reactant Product Energy must be supplied. Energy supplied Energy released Reactant Product Energy is released.

8 Activation Energy Activation energy refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction. – catalyst - substance that lowers the activation energy  cannot violate laws of thermodynamics.  direction of a chemical reaction is determined solely by the difference in free energy between the reactants and the products

9 Activation Energy and Catalysis

10 Enzymes Are Biological Catalysts Enzymes are proteins that carry out most catalysis in living organisms. – Unique three-dimensional shape enables an enzyme to stabilize a temporary association between substrates.  Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and can then be reused.

11 Enzymes Most enzymes are globular proteins with one or more active sites. – Substrates bind to the enzyme at these active sites, forming an enzyme-substrate complex. The substrate, sucrose, consists of glucose and fructose bonded together. 1 The substrate binds to the enzyme, forming an enzyme- substrate complex. 2 The binding of the substrate and enzyme places stress on the glucose- fructose bond, and the bond breaks. 3 Products are released, and the enzyme is free to bind other substrates. 4 Bond Enzyme Active site H2OH2O GlucoseFructose

12 Enzyme Forms A multienzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another. – subunits work in concert, providing significant advantages in catalytic efficiency RNA catalysts “ribozymes”

13 Factors Affecting Enzyme Activity Temperature – Rate of an enzyme- catalyzed reaction increases with temperature, but only up to an optimum temperature. pH – Ionic interactions also hold enzymes together. 30 Optimum temperature for human enzyme Optimum temperature for enzyme from hotsprings prokaryote Optimum pH for pepsin Temperature of reaction (°C) pH of reaction Optimum pH for trypsin Rate of reaction

14 Factors Affecting Enzyme Activity Inhibitors and activators – inhibitor - substance that binds to an enzyme and decreases its activity  competitive inhibitors - compete with the substrate for the same active site  noncompetitive inhibitors - bind to the enzyme in a location other than the active site  allosteric sites - specific binding sites acting as on/off switches Competitive inhibition Noncompetitive inhibition Competitive inhibitor interferes with active site of enzyme so substrate cannot bind Allosteric inhibitor changes shape of enzyme so it cannot bind to substrate Enzyme Substrate Enzyme Substrate

15 Factors Affecting Enzyme Activity – activator - substances that bind to allosteric sites and keep the enzymes in their active configurations  increase enzyme activity  cofactors - chemical components that facilitate enzyme activity  coenzyme

16 ATP Adenosine triphosphate (ATP) is the chief energy currency of the cell. – Each molecule is a nucleotide composed of ribose, adenine, and a triphosphate group.  energy stored in the triphosphate group  cell uses ATP to drive endergonic reactions

17 Biochemical Pathways Biochemical pathways are the organizational units of metabolism. – Metabolism is the total of all chemical reactions carried out by an organism.  anabolism - reactions that expend energy  catabolism - reactions that harvest energy Product Enzyme 1 Enzyme 3 Enzyme 4 Substrate Enzyme 2

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19 Regulation of Biochemical Pathways Biochemical pathways must be coordinated and regulated to operate efficiently. – advantageous for cell to temporarily shut down biochemical pathways when their products are not needed  feedback inhibition - When the cell produces increasing quantities of a particular product, it automatically inhibits its ability to produce more.

20 Feedback Inhibition

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22 Summary Flow of Energy in Living Things Laws of Thermodynamics Free Energy Activation Energy Enzymes – Forms – Activity ATP Biochemical Pathways

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