Chapter 7: Cellular Respiration How Cells Make ATP: Energy-Releasing Pathways

FYI Coupled reactions (otherwise known as oxidation-reduction reactions - REDOX ), fermentation, cell respiration and photosynthesis are some of the most challenging concepts in biology. Note that questions on the AP Biology Exam are most likely to focus on the net results of photosynthesis and respiration and not on the exact reactions that create the products.

Summary: Cellular respiration - the process by which your cells transfer the energy in organic compounds to ATP. The byproduct of this reaction is water and carbon dioxide. It occurs in the cells mitochondria, which are the energy producers for the cell.

Summary: Each cell converts the energy in the chemical bonds of nutrients to chemical energy stored in ATP May be aerobic or anaerobic Most cells use aerobic respiration 3 pathways that are exergonic and release energy: Aerobic respiration Anaerobic respiration Fermentation

Aerobic Respiration Most eukaryotes and prokaryotes Requires oxygen To obtain energy from glucose Requires oxygen Nutrients are catabolized to CO2 and H2O Glucose + Oxygen Carbon Dioxide + Water + Energy (in bonds of ATP)

Aerobic Respiration A redox process Glucose is oxidized to form Carbon Dioxide Oxygen is reduced, forming water The electrons produced are used to form ATP

Aerobic Respiration 3 stages: Glycolysis Citric Acid (Krebs) Cycle Electron Transport Chain and Chemiosmosis

Aerobic Respiration *In eukaryotes, glycolysis occurs in cytosol and remaining 2 steps occur in mitochondria. * In bacteria, all stages occur in cytosol working with plasma membrane.

Glycolysis Occurs in cytosol Glucose converted to two 3-carbon molecules of pyruvic acid ATP and NADH are formed NADH - temporarily stores large amounts of free energy Energy from NADH ultimately participates in reactions that form ATP Net production of 2 ATP Animation of Glycolysis

Advantages of Glycolysis The process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds. Glycolysis does not require oxygen.

Citric Acid Cycle (Krebs Cycle) Pyruvic Acid from Glycolysis moves into mitochondria. Pyruvic acid breaks apart 1 molecule of CO2 is produced 2 other Carbon atoms form acetyl CoA Acetyl CoA combines with 4 carbon molecules to produce citric acid.

Citric Acid Cycle (Krebs Cycle) Citric Acid is broken down CO2 released Electrons transferred to energy carriers. Carbon Dioxide is a waste product ATP, NADH and FADH2 are produced 2 ATP are produced/glucose

Electron Transport Chain and Chemiosmosis Electrons from Krebs cycle are passed to NADH and FADH2 in Electron Transport Chain Enzymes present in mitochondrial membrane As NADH and FADH2 pass along enzymes, they give up electrons (energy) = chemiosmosis H+ ions are transported across membrane and come in contact with ATP synthase ADP + Pi = ATP

End of chain – electrons combined with oxygen and hydrogen to form water Via chemiosmosis, 34 ATP produced. ATP synthesis continues until ADP stores are depleted

Equation C6H12O6 + 6O2 -->6 CO2 + 6H2O + 38 ATP

Aerobic Respiration – End Results One glucose gives maximum of 36-38 ATP’s Glycolysis produces 2 ATP molecules 2 ATP molecules are produced in the citric acid cycle Remainder of ATP is produced in the electron transport system (32 or 34) Efficiency is about 40%; remaining energy is disseminated as heat

Other nutrients (besides glucose) provide energy More energy is gained from burning fats than glucose Lipids contain 9 kcal/gram Lipids are broken down and glycerol enters glycolysis Fatty acids are converted to acetyl CoA and enter the citric acid cycle Proteins are broken down to amino acids Proteins contain 4 kcal/gram

Anaerobic Respiration and Fermentation do not Require Oxygen Various inorganic substances serve as the final electron acceptor Yield is only the 2 ATP molecules from glycolysis Types of Fermentation Alcohol Lactate

Alcoholic Fermentation Alcoholoic fermentation Alcoholic fermentation produces ethanol Pyruvate is converted to ethanol Ethanol is a potentially toxic waste product Yeast carry out alcoholic fermentation when oxygen deprived Pyruvic acid + NADH -> alcohol + CO2 + NAD+

Lactate Fermentation Bacteria and some fungi carry out lactate fermentation Strenuous exercise in mammals results in lactate fermentation as well Yields only the 2 ATP molecules from glycolysis Pyruvic acid + NADH -> lactic acid + NAD+

Copyright Pearson Prentice Hall Fermentation Lactic acid fermentation converts glucose into lactic acid. The first part of the equation is glycolysis. The second part shows the conversion of pyruvic acid to lactic acid. Copyright Pearson Prentice Hall

Group Assignment: Glycolysis Krebs Cycle Electron Transport Chain/Chemiosmosis Alcoholic Fermentation Lactate Fermentation