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)

Outline• Energy and Metabolism

Enzymes (cntd.)

• Cellular Respiration

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.

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 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”

Mechanisms of Enzyme Inhibition

Molecules that Regulate Enzyme Action

2. Activators

Bind to enzymes to increase their activity.

Usually bind to allosteric sites.

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.

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+)

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 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