Chapter 8: An Introduction to Metabolism What is metabolism? All of an organisms chemical processes What are the different types of metabolism? Catabolism – releases energy by breaking down complex molecules Anabolism – use energy to build up complex molecules Catabolic rxns – hydrolysis – break bonds Anabolic rxns – dehydration – form bonds How is metabolism regulated? Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product

Chapter 8: An Introduction to Metabolism 4. What are the different forms of energy? - Kinetic – energy from molecules in motion - Potential – energy based on location or structure - water behind a dam - bonds in gas/oil - Chemical energy – bio speak for potential energy that can be released in a catabolic rxn

Figure 8.2 Transformation between kinetic and potential energy On the platform, a diver has more potential energy. Diving converts potential energy to kinetic energy. Climbing up converts kinetic energy of muscle movement to potential energy. In the water, a diver has less potential energy.

Chapter 8: An Introduction to Metabolism 5. What are the 2 laws of thermodynamics? - 1st law – Energy is constant. It can be transferred or transformed but it cannot be created or destroyed. - 2nd law – Every transfer or transformation of energy increases the entropy (disorder) of the universe. (a) First law of thermodynamics: Energy can be transferred or transformed but neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b). Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. (b) Chemical energy Heat co2 H2O +

Chapter 8: An Introduction to Metabolism What is the difference between exergonic & endergonic rxns? - Exergonic – releases energy - Endergonic – require energy - Catabolic rxns – hydrolysis – break bonds – exergonic - Anabolic rxns – dehydr. syn. – form bonds – endergonic 7. Where does the energy come from to drive rxns in the body? - ATP CH –O O CH2 H OH N C HC NH2 Adenine Ribose O– P Phosphate groups

Chapter 8: An Introduction to Metabolism 8. How does ATP provide energy? - hydrolysis of ATP P Adenosine triphosphate (ATP) H2O + Energy Inorganic phosphate Adenosine diphosphate (ADP) P i

Figure 8.10 Energy Coupling: Use an exergonic reaction to fuel an endergonic reaction!!! Endergonic reaction (dehydration synthesis of NH2 and Glu): ∆G is positive, reaction is not spontaneous ∆G = +3.4 kcal/mol Glu ∆G = –7.3 kcal/mol ATP H2O + NH3 ADP NH2 Glutamic acid Ammonia Glutamine Exergonic reaction (hydrolysis of ATP): ∆ G is negative, reaction is spontaneous P Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol

Figure 8.11 How ATP drives cellular work + P Motor protein P i Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ATP Solute P i ADP Solute transported (b) Transport work: ATP phosphorylates transport proteins Glu NH3 NH2 (c) Chemical work: ATP phosphorylates key reactants Reactants: Glutamic acid and ammonia Product (glutamine) made

Figure 8.12 The ATP cycle ATP synthesis from ADP + P i requires energy (endergonic) ATP ADP + P i Energy for cellular work (such as dehydration synthesis!) Energy from catabolism (breaking down food molecules via hydrolysis) ATP hydrolysis to ADP + P i yields energy (exergonic)

Chapter 8: An Introduction to Metabolism 9. What is an enzyme? - biological catalyst made of protein 10. How do enzymes work? - lower energy of activation (EA) - EA = energy reactants must absorb before the rxn can start

Figure 8.14 Energy profile of an exergonic reaction D B Transition state Products Progress of the reaction ∆G < O Reactants Free energy EA The reactants AB and CD must absorb enough energy from the surroundings to reach the unstable transition state, where bonds can break. Bonds break and new bonds form, releasing energy to the surroundings.

Figure 8.15 The effect of enzymes on reaction rate. Progress of the reaction Products Course of reaction without enzyme Reactants with enzyme EA EA with is lower ∆G is unaffected by enzyme Free energy

Chapter 8: An Introduction to Metabolism Some enzyme terms - substrate – what the enzyme works on – substrate-specific - active site – where the substrate binds to the enzyme - induced fit – molecular handshake – when the enzyme binds to the substrate, it wraps around the substrate Substrate Active site Enzyme (a) (b) Enzyme- substrate complex

Figure 8.17 The active site and catalytic cycle of an enzyme

How does it work? Variety of mechanisms to lower activation energy & speed up reaction Dehydration synthesis active site orients substrates in correct position for reaction/brings substrates closer together Hydrolysis active site binds substrate & puts stress on bonds that must be broken, making it easier to separate molecules 17

Enzymes in REAL LIFE! 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) 18

Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? - temperature - pH Optimal pH for two enzymes Rate of reaction 20 40 60 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes (b) Optimal pH for two enzymes pH Optimal temperature for typical human enzyme enzyme of thermophilic Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) 1 2 3 4 5 6 7 8 9 10 (heat-tolerant) bacteria

Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? - temperature - pH - cofactors – inorganic non-protein helpers of enzyme activity (Zn, Fe, Cu) - coenzymes – organic cofactors (vitamins) - inhibitors - competitive – compete w/ substrate for active site -PENICILLIN – blocks enzyme that bacteria use to build cell walls - non-competitive – bind remotely (not to active site, but to secondary site called ALLOSTERIC SITE,) thus changing enzyme shape & inhibiting activity -CYANIDE – changes shape of enzyme necessary to make ATP during cellular respiration

Figure 8.19 Inhibition of enzyme activity A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Competitive inhibitor (a) Normal binding (b) Competitive inhibition A substrate can bind normally to the active site of an enzyme. A competitive inhibitor mimics the substrate, competing for the active site. Substrate Active site Enzyme Noncompetitive inhibitor (c) Noncompetitive inhibition

Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? 13. How are enzymes regulated? - allosteric inhibitors -keeps enzyme inactive - allosteric activators -keeps enzyme active Stabilized inactive form Allosteric activater stabilizes active from Allosteric enyzme with four subunits Active site (one of four) Regulatory site (one of four) Active form Activator Stabilized active form Allosteric inhibiter stabilizes inactive form Inhibitor Inactive form Non- functional active site Oscillation

Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? 13. How are enzymes regulated? - allosteric inhibitors - allosteric activators

Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? 13. How are enzymes regulated? - allosteric inhibitors - allosteric activators - feedback inhibition -final product is inhibitor of earlier step! -prevents unnecessary accumulation of product Active site available Isoleucine used up by cell Feedback inhibition Isoleucine binds to allosteric site Active site of enzyme 1 no longer binds threonine; pathway is switched off Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine)