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Bio 178 Lecture 14Metabolism and Respiration
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Reading
• Chapters 8 & 9
Quiz Material
• Questions on P 158 & 184
• Chapters 8 & 9 Quizzes on Text Website (www.mhhe.com/raven7)
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Outline• Energy and Metabolism
Enzymes (cntd.)
• Cellular Respiration
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Environmental Effects on Enzyme CatalysisAffected by anything that alters its 3D shape:pH, [salt], temperature, regulatory molecules
Temperature• Optimum Temperature
Temperature at which reaction rate is greatest.
• Below Optimum
Increasing temp increases substrate-enzyme collisions & can stress bonds.
Bonds not flexible to permit induced fit not optimum.
• Above Optimum
Denaturation.
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Effect of Temperature on Enzyme Catalysis
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Environmental Effects on Enzyme Catalysis
pH
• Optimum pH
pH at which reaction rate is greatest.
• Above/Below Optimum
Change in [H+] affects charge balance between charged amino acids, which affects intramolecular bonding.
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Effect of pH on Enzyme Catalysis
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Molecules that Regulate Enzyme Action1. InhibitorsBind to enzymes to decrease their activity.• Function Regulation of metabolic pathways, eg. Feedback inhibition.
• Inhibitory Mechanisms
(a) Competitive Inhibitors
Compete with the substrate for the active site.
(b) Noncompetitive Inhibitors
Bind to enzyme in a regulatory site other than the active site conformational change.
Eg. Allosteric site - “on/off switches”
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Mechanisms of Enzyme Inhibition
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Molecules that Regulate Enzyme Action
2. Activators
Bind to enzymes to increase their activity.
Usually bind to allosteric sites.
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Enzyme CofactorsNon-protein “helpers” that aid in some enzyme catalyzed reactions.
• How do they Work?
Draw electrons away from covalent bonds in the substrate weaken bonds.
• Inorganic Cofactors
Example - Metal ions like zinc, molybdenum, & manganese.
• Coenzymes
Non-protein organic cofactors, eg. Vitamins.
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Coenzymes and Redox ReactionsCoenzymes (electron acceptors) shuttle energy from one enzyme to the next - pass energy with pairs of electrons from one substrate to the next in a reaction series.
Example: Nicotinamide adenine dinucleotide (NAD+)• Composition
2 nucleotides (NMP + AMP).
• Functions of its constituent parts
AMP - Core (conformation recognized by enzyme)
NMP - Electron acceptor
• Reduction of NAD+
NAD+ + 2H NADH + H+ (2 electrons & 1 H+ transferred to NAD+)
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Structure of NAD+
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Biochemical Pathways - Metabolism
• Anabolic Reactions
Biosynthetic part of metabolism - Energy expended to synthesize materials.
• Catabolic Reactions
Part of metabolism involved in hydrolyzing macromolecules - usually harvest energy.
• Biochemical Pathways
Sequences in which the products of one enzyme controlled reaction are the substrates for the next in a series of reactions.
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Biochemical Pathways
McGraw-Hill Video
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Regulation of Biochemical Pathways
• Why Regulate?
Save energy when a product is not needed.
• How is Regulation Achieved?
Feedback inhibition.
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Feedback inhibition
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Feedback Inhibition
McGraw-Hill Video
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How do Organisms Obtain Energy?
• Chemical bonds contain energy - these bonds must be broken to extract the energy.
• Energy (potential) is obtained from the electrons in the bond.
Step 1 - Digestion
Enzymes break the large molecules into smaller ones.
Step 2 - Catabolism
Enzymes break down the smaller molecules step by step, harvesting energy at each step.
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Cellular Respiration
The metabolic harvesting of energy by oxidation. The electrons (& the energy) are transferred from one molecule to the next, losing energy as they go.
Types of Cellular Respiration• Aerobic
Final electron acceptor is oxygen.
• Anaerobic
Final electron acceptor is an inorganic molecule other than oxygen.
• Fermentation
Final electron acceptor is an organic molecule.
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Cellular Respiration (Cntd.)
• Overall Reaction
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
• ∆G-720 kcal/mole of glucose (cellular conditions)
Negative sign: Products contain less energy than reactants.
• Where does the Energy Released Go?
Cells harvest some of it to make ATP.
The rest is released as heat.
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Using ATP to Provide Energy
How is energy released from ATP?
The transfer of a phosphate group to another molecule relaxes the ATP (electrostatic repulsion).
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ATP Synthase
Makes most of the ATP produced by the cell.
What is the energy source for ATP synthase?
• Protons diffuse into the cell through ATP synthase.
• This releases energy.
• The energy is used by ATP synthase to rotate.
• This mechanical energy is converted to chemical energy by adding a third phosphate to ADP.
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ATP Synthase
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Glucose Catabolism
Methods for Making ATP
1. Substrate-Level Phosphorylation
ADP + Pi ATP
Pi comes from a phosphate bearing intermediate molecule.
Example - Glycolysis.
2. Aerobic Respiration
ATP synthase makes ATP using energy provided by electron transfer. O2 = final electron acceptor.
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Substrate-Level Phosphorylation
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Aerobic Respiration
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Processes Involved in Eukaryotic Respiration1. GlycolysisSugar splitting anaerobic process.
• Location
Cytoplasm
• Energetic Products2 ATP net & 2 NADH net produced by substrate level phosphorylation.
2. Aerobic Respiration• Pyruvate oxidation
• Krebs cycle
• Electron transport chain