How Cells Harvest Energy

Chapter 9

Outline

•Metabolism

•Glucose Catabolism

–Glycolysis

–Pyruvate Oxidation

–Krebs Cycle

–Electron Transport Chain      

•Aerobic Respiration Summary

•Energy Storage

•Fermentation

 

Using Chemical Energy to Drive Metabolism

•Autotrophs - Convert radiant energy into chemical energy.

•Heterotrophs - Use energy autotrophs produce.

–Digestion – Break down large molecules w/ enzymes.

–Catabolism - Harvesting energy from C-H.

 

Using Chemical Energy to Drive Metabolism

•Aerobic Respiration

–O2 gas accepts the H+ = H20

–C6H12O6 + 6 O2 เ 6 CO2 + 6 H20 + energy

•Anaerobic Respiration - Occurs when an inorganic molecule other than O2 accepts H+

–Fermentation - Occurs when an organic molecule accepts the H+

 

ATP

•ATP serves as cell’s energy currency.

–Locomotion

–Endergonic Reactions

•Enzyme driving reaction has two binding sites.  One for the reactant and one for ATP.

–Energy released from ATP pushes  reactant at the site up the gradient.

 

Overview of Glucose Catabolism

•Cells catabolize organic molecules two ways:

–Substrate-Level Phosphorylation

•Glycolysis

–Aerobic Respiration

•Pyruvate Oxidation

•Krebs Cycle

•Electron Transport Chain

 

Aerobic Respiration Overview

 

Overview of Glucose Catabolism

•Glycolysis

–Produces two ATP (net gain) molecules for each molecule of glucose

 

Overview of Glucose Catabolism

•Anaerobic Respiration

–W/o oxygen, some organisms can still respire anaerobically, using inorganic molecules to accept electrons.

•Methanogens

•Sulfur Bacteria

 

Glycolysis

•All Cells Use Glycolysis

–more energy from glucose through aerobic respiration (follows glycolysis in organisms w/ mitochondria)

 

Glycolysis

•2 NAD+ reduced to NADH. 

•NAD+ must be regenerated

–Aerobic Respiration

–Fermentation

 

Oxidation of Pyruvate

•In stage two of glucose catabolism, pryuvate yields:

–acetylCoA

–NADH

–CO2.

•Occurs within mitochondria.

 

Krebs Cycle

•Krebs Cycle - 2 ATP per glucose.

–NADH

–FADH2

–Both to electron transport chain

–CO2 = waste

 

Electron Extraction

•Oxidation-reduction reactions release energy of electrons by transferring them to oxygen atoms.

•Energy is harvested from glucose in gradual steps, using NAD+ and FAD as electron carriers

 

Electron Transport Chain

•Electrons from glucose pumped out of mitochondrial matrix by electron transport chain (into intermembrane space)

–Return of protons onto the matrix generates ATP (through channel proteins)

 

Summarizing Aerobic Respiration

•Oxidative reduction produces 30 ATP from each glucose in eukaryotic cells.

–1/3 energy in glucose.

 

Regulating Aerobic Respiration

•Relative levels of ADP and ATP regulate the catabolism of glucose at key committing reactions.

 

Energy Storage

•Proteins, fats, and other organic molecules are also metabolized for energy.

–Converted to pyruvate or Acetyl-CoA first.

 

Fermentation

•Fermentation occurs in the absence of oxygen.

–Electrons donated to organic molecule regenerating NAD+ from NADH.

 

Lactic Acid Fermentation

•Lactate dehydrogenase NADH back into NAD+

•Leave lactic acid as waste product

•Removed by blood (can only take so much)

•Muscle fatigue & soreness