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Transcript
Chapter 8: An Introduction to Metabolism 1. What is metabolism? • All of an organisms chemical processes 2. 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 3. How is metabolism regulated? Enzyme 1 A Enzyme 3 D C B Reaction 1 Starting molecule Enzyme 2 Reaction 2 Reaction 3 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. Climbing up converts kinetic energy of muscle movement to potential energy. Diving converts potential energy to kinetic 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. Heat Chemical energy (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). co2 + H2O (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. Chapter 8: An Introduction to Metabolism 6. 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? Adenine NH - ATP 2 N O –O P O– O P O– O P O N CH2 N C CH O O– H Phosphate groups C HC O O C H H Ribose H OH OH N Chapter 8: An Introduction to Metabolism 8. How does ATP provide energy? - hydrolysis of ATP P P P Adenosine triphosphate (ATP) H2O Pi + Inorganic phosphate P P Adenosine diphosphate (ADP) Energy 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 NH2 Glu + Glutamic acid NH3 Glu Ammonia Glutamine ∆G = +3.4 kcal/mol Exergonic reaction (hydrolysis of ATP): ∆ G is negative, reaction is spontaneous ATP + H2O ADP + Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous P ∆G = –7.3 kcal/mol ∆G = –3.9 kcal/mol Figure 8.11 How ATP drives cellular work P i P Motor protein Protein moved (a) Mechanical work: ATP phosphorylates motor proteins Membrane protein ADP + ATP P Pi P Solute Solute transported (b) Transport work: ATP phosphorylates transport proteins P Glu + NH3 Reactants: Glutamic acid and ammonia NH2 + P i Glu Product (glutamine) made (c) Chemical work: ATP phosphorylates key reactants i Figure 8.12 The ATP cycle ATP synthesis from ADP + P i requires energy (endergonic) ATP hydrolysis to ADP + P i yields energy (exergonic) ATP Energy from catabolism (breaking down food molecules via hydrolysis) ADP + P i Energy for cellular work (such as dehydration synthesis!) 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 The reactants AB and CD must absorb enough energy from the surroundings to reach the unstable transition state, where bonds can break. A B C D Bonds break and new bonds form, releasing energy to the surroundings. Free energy Transition state A B C D EA Reactants A B ∆G < O C D Products Progress of the reaction Figure 8.15 The effect of enzymes on reaction rate. Course of reaction without enzyme EA without enzyme Free energy EA with enzyme is lower Reactants ∆G is unaffected by enzyme Course of reaction with enzyme Products Progress of the reaction Chapter 8: An Introduction to Metabolism 11. 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- substrate complex Enzyme (a) (b) 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 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) Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? - temperature - pH Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Rate of reaction Optimal temperature for typical human enzyme 0 60 40 20 80 100 Temperature (Cº) (a) Optimal temperature for two enzymes Rate of reaction Optimal pH for pepsin (stomach enzyme) 0 1 2 3 4 5 pH Optimal pH for trypsin (intestinal enzyme) 6 OptimalpH for two two enzymes enzymes (b) Optimal pH for 7 8 9 10 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 substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A competitive inhibitor mimics the substrate, competing for the active site. 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 (b) Competitive inhibition Noncompetitive inhibitor (c) Noncompetitive inhibition Chapter 8: An Introduction to Metabolism 12. What affects enzyme activity? Allosteric activater 13. How are enzymes regulated? stabilizes active from Allosteric enyzme Active site with four subunits (one of four) - allosteric inhibitors -keeps enzyme inactive Regulatory - allosteric activators site (one Activator -keeps enzyme active of four) Active form Stabilized active form Oscillation Allosteric inhibiter stabilizes inactive form NonInactive form Inhibitor functional active site Stabilized inactive form 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 Active site available -final product is inhibitor of earlier step! -prevents unnecessary accumulation of product Threonine in active site Enzyme 1 (threonine deaminase) Isoleucine used up by cell - feedback inhibition Initial substrate (threonine) Intermediate A Feedback inhibition Active site of enzyme 1 no longer binds threonine; pathway is switched off Enzyme 2 Intermediate B Enzyme 3 Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 End product (isoleucine)