Chemical Pathways  Cellular Respiration (aerobic) – process that releases energy by breaking down glucose and other food molecules; O 2 is required  6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + ATP  3 Major sets of reactions – glycolysis, Krebs Cycle, electron transport chain electron transport chain  Fermentation (anaerobic) – process that releases energy from food without O2 – Fig. 9-4  2 Major sets of reactions – glycolysis, fermentation  NADH – an electron carrier molecule

Glycolysis – breakdown of glucose to produce: 2 pyruvic acid, 2 NADH, **net gain of 2 ATP produce: 2 pyruvic acid, 2 NADH, **net gain of 2 ATP

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Fermentation – conversion of pyruvic acid to some end product ** no ATP produced ** no ATP produced

Lactic acid fermenation – end product is lactic acid (ex. Animal cells, lactic acid bacteria)

Alcoholic fermentation – end products are ethanol & CO2 (ex. Bacteria & yeast)

**For each molecule of glucose only 2 ATP are produced during anaerobic respiration.**

Glycolysis – exact same steps as in anerobic respiration; takes place in the cytoplasm; At the end of glycolysis approximately 90% of the energy is still stored in pyruvic acid molecules These two pyruvic acid molecules will enter the Krebs Cycle (citric acid cycle)

Glycolysis

Krebs cycle (citric acid cycle) – the two pyruvic acids molecules that are products of glycolysis are broken down in a series of energy- extracting reactions Takes place in the matrix of the mitochondria

Krebs cycle (con’t) 1. Citric Acid Production – pyruvic acid is completely oxidized to produce: a. 2 NADH b. 2 CO 2 c. 2 Citric Acid molecules

Krebs cycle (con’t) 2. Energy extraction – series of chemical reactions (cycle) to produce (for each pyruvic acid) a. 1 ATP (2 ATP total) b. 3 NADH (6 NADH total) c. 1 FADH (2 FADH total) d. 2 CO 2 (4 CO 2 total) =related =related

Electron Transport Chain – uses the high energy electrons from glycolysis and the Krebs cycle to synthesize ATP from ADP and Pi MOST of the energy produced from the breakdown of glucose occurs here (32/34 ATP molecules) O 2 is the final electron acceptor

***For each molecule of glucose, 36/38 ATP are produced during aerobic respiration*** ***Much more energy efficient than anaerobic respiration****

Fats and proteins are broken down at various points along respiratory pathway Proteins produce about the same amount of ATP as glucose Fats produce about twice as much energy as glucose

The body uses ATP from 3 basic sources; ATP stored in muscle cells, and ATP produced by aerobic & anaerobic respiration The ATP stored in muscle cells only lasts for the first few seconds of activity.

ATP produced by anaerobic respiration is used up in about 90 seconds. Oxygen debt is the amount of O 2 required to convert lactic acid to glucose. Aerobic respiration produces the ATP to sustain activities that go on longer. That is why athletes must pace themselves.