3.7 Cell Respiration By: Zachary Novatt June 06, 2008

Cell Respiration: The controlled release of energy from organic compounds in cells to form ATP (Adenosine triphosphate). It is “the most prevalent and efficient catabolic energy-yielding pathway for the production of ATP, in which oxygen is consumed as a reactant along with the organic fuel.” Define cell respiration -Campbell 155

In cell respiration, glucose (a six carbon sugar) in the cytoplasm is oxidized and broken down through glycolysis (“splitting of sugar”) into two molecules of pyruvate (a three carbon sugar), with a small net yield of 2 ATP plus 2 NADH. No CO₂ is released here and glycolysis occurs whether or not O₂ is present State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP. Campbell pages:

3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP Anaerobic catabolism of organic nutrients can occur through fermentation. Fermentation is an extension of glycolysis and generates 2 ATP through substrate-level phosphorylation (with use of NAD+ ). There is no further yield of ATP because NAD+ will deplete because it will cease to be recycled from NADH without the oxygen required in oxidative phosphorylation. There are two types of fermentation alcohol (in yeast) and lactic acid (in humans). In alcohol fermentation pyruvate is converted into ethanol by the releasing of carbon dioxide and the remaining acetaldehyde being reduced by NADH. During lactic acid fermentation pyruvate is reduced by NADH to form lactate without releasing carbon dioxide. Lactate in humans causes muscle fatigue and pain. Campbell pages:

3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP. When pyruvate enters the mitochondria it goes through oxidative decarboxylation where it loses a carbon dioxide and is converted into acetyl coenzyme A (acetyl CoA), a two-carbon molecule. This is called the link reaction. When it enters the Krebs cycle it is oxidized to carbon dioxide and chemical energy is released then converted into 6 NADH (most of the energy), 4 FADH₂, and a net of 4 ATP. Then the NADH and FADH₂ enter the electron transport chain in the inner membrane of the mitochondria. NADH and FADH₂ (at a later stage) pass on electrons giving up energy in the form of ATP as they are passed on from one carrier to another. At the end of the E.T.C. the electrons are given to oxygen and at the same time oxygen accepts hydrogen ions to form water. This is called oxidative phosphorylation. At the end of the E.T.C. 36 ATP are produced per molecule of glucose. Campbell pages:

Vocabulary List Fermentation Oxidation Reduction NAD+ Electron Transport Chain Oxidative phosphorylation Substrate-level phosphorylation Glycolysis Krebs cycle Acetyl CoA ATP synthase Proton-motive force Chemiosmosis FADH₂ Aerobic respiration Anaerobic respiration Alcohol fermentation Lactic acid fermentation Beta oxidation