Introduction Before food can be used to perform work, its energy must be released through the process of respiration. Two main types of respiration exist in living things. Both begin with glycolysis. Glycolysis: a process by which one glucose molecule is broken down into two pyruvic acid molecules. Fermentation (anaerobic respiration): pyruvic acid is broken down without the use of oxygen Oxidative Respiration (aerobic respiration): pyruvic acid is metabolized using oxygen

Glycolysis Glycolysis occurs in the cytoplasm. It does not require oxygen. Each of its steps is catalyzed by a specific enzyme.

Glycolysis

Glucose ATP ADP + P G3P G3P + P Pyruvic Acid NADH + H + 2 ADP + 2 P 2 ATP NAD H e - NAD H e -

Fermentation

Fermentation (Anaerobic Respiration) Fermentation is the breakdown of pyruvic acid without the use of oxygen. Glycolysis + Fermentation = Anaerobic Respiration The metabolism of pyruvic acid during fermentation does not produce any ATP. Instead, the function of fermentation is to break down pyruvic acid and regenerate NAD + for reuse in glycolysis.

Pyruvic Acid NADH + H + NAD H e - Lactic Acid Pyruvic Acid NADH + H + NAD H e - Ethyl Alcohol (Ethanol) CO 2 Lactic Acid Fermentation Alcoholic Fermentation To Glycolysis

Oxidative Respiration

Aerobic Respiration The result of glycolysis and aerobic respiration is shown by the reaction: C 6 H 12 O O 2 → 6 H 2 O + 6 CO ATP Aerobic respiration occurs in the mitochondria outer and inner membrane matrix: dense solution enclosed by inner membrane cristae: the folds of the inner membrane that house the electron transport chain and ATP synthase Steps: Conversion of Pyruvic Acid Kreb’s Cycle Electron Transport Chain

Structure of Mitochondrion

Kreb’s Cycle The Krebs Cycle is the central biochemical pathway of aerobic respiration. It is named after its discoverer, Sir Hans Krebs. Because citric acid is formed in the process, it is also known as the Citric Acid Cycle.

Conversion of pyruvic acid (PA) Kreb’s Cycle

NADH + H + NAD + CoA NAD + NADH + H + NAD + NADH + H + FAD FADH 2 ATP ADP + P CO 2 C Pyruvic Acid CCC Acetyl-CoA CC Citric Acid CCCCCC CO 2 C Ketoglutaric Acid CCCCC Succinic Acid CCCC CO 2 C Malic Acid CCCC Oxaloacetic Acid CCCC

Electron Transport Chain Glycolysis, the conversion of PA to acetyl-CoA, and the Krebs Cycle complete the breakdown of glucose. Up to this point: 4 ATP (2 from glycolysis, 2 from Krebs) 10 NADH (2 from glycolysis, 2 from the conversion of PA, 6 from Krebs) 2 FADH 2 (from Krebs)

Electron Transport Chain NADH + H + and FADH 2 carry electrons to an electron transport chain, where additional ATP is produced. 8 NADH24 ATP (WHY????) 2 FADH2 4 ATP (WHY????) 2 NADH 4 ATP (WHY????)

Electron Transport Chain

Electron Transport Hydrogen Ion Movement ATP Production ATP synthase Channel Inner Membrane Matrix Intermembrane Space

Energy Yield Aerobic respiration produces a maximum of 36 ATP. 2 ATP from Glycolysis 2 ATP from Krebs 32 ATP from ETC Reasons why ATP yield can be less than 38: Sometimes energy is required to transport NADH formed by glycolysis from the cytoplasm into the mitochondria. Some H + in chemiosmosis may not be recycled and/or wasted

Energy Yield

Aerobic Respiration is generally 18 times more efficient than anaerobic respiration. The ATP produced during aerobic respiration represents about 1/2 of the energy stored in a molecule of glucose.