Transcript Biol 178 Lecture 14

Bio 178 Lecture 14
Metabolism 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)
Outline
•
Energy and Metabolism
 Enzymes (cntd.)
• Cellular Respiration
Environmental Effects on Enzyme Catalysis
Affected 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.
Effect of Temperature on Enzyme Catalysis
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.
Effect of pH on Enzyme Catalysis
Molecules that Regulate Enzyme Action
1. Inhibitors
Bind 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”
Mechanisms of Enzyme Inhibition
Molecules that Regulate Enzyme Action
2. Activators
Bind to enzymes to increase their activity.
Usually bind to allosteric sites.
Enzyme Cofactors
Non-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.
Coenzymes and Redox Reactions
Coenzymes (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+)
Structure of NAD+
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.
Biochemical Pathways
McGraw-Hill Video
Regulation of Biochemical Pathways
• Why Regulate?
Save energy when a product is not needed.
• How is Regulation Achieved?
Feedback inhibition.
Feedback inhibition
Feedback Inhibition
McGraw-Hill Video
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.
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.
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.
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).
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.
ATP Synthase
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.
Substrate-Level Phosphorylation
Aerobic Respiration
Processes Involved in Eukaryotic Respiration
1. Glycolysis
Sugar splitting anaerobic process.
• Location
Cytoplasm
• Energetic Products
2 ATP net & 2 NADH net produced by substrate level
phosphorylation.
2. Aerobic Respiration
• Pyruvate oxidation
• Krebs cycle
• Electron transport chain