Harvesting Chemical Energy Cellular Respiration Harvesting Chemical Energy

Metabolism All organisms have metabolic pathways Each step of the pathway is controlled by different enzymes Eukaryotic organelles compartmentalize pathways

Glucose Most organisms use glucose (C6H12O6) as a source of energy Cells oxidize glucose for energy Energy is typically captured as ATP Can involve as many as 3 pathways: Glycolysis, Cellular Respiration, Chemiosmosis Aerobic produces 38 ATP; anaerobic 2

Oxidation/Reduction Reactions The gain of electrons or hydrogen atoms is called reduction The loss of electrons or hydrogen atoms is called oxidation Oxidation and reduction reactions are always coupled

NAD (nicotinamide adenine dinucleotide) May exist as NAD+ (oxidized) or NADH(reduced) The oxidation of NADH produces energy

Glycolysis Occurs in the cytoplasm of the cell Anaerobic Produces two molecules of pyruvate, two ATP, and two NADH Some steps are endergonic (require energy)

Glycolysis Diagram

Key Points of Glycolysis Begins with a 6-C sugar that is converted into two 3-C sugars Produces two G3P (glyceraldehyde 3-phosphate) molecules ATP is used as a source for phosphate groups and energy Energy producing steps occur when phosphate groups are transferred to ADP from ATP and NAD+ is reduced ATP is produced by substrate level phosphorolation Two ATPs are used and 4 are produced with a net gain of two ATPs

Acetyl COA Production Occurs on the inner mitochondrial membrane CO2 is liberated and NADH+H and Acetyl COA is produced

Diagram of acetyl COA production

Citric Acid Cycle Consists of eight reactions Majority takes place in the mitochondrial matrix Each time CO2 is released NAD is reduced Each cycle produces: two CO2 molecules, Reduces three NAD, One FADH2 , and one ATP

Diagram of the Citric acid Cycle

Electron Transport Chain Involves the passing of electrons through a series of membrane associated electron carriers in the mitochondria to produce ATP The respiratory chain is composed of enzymes that shuttle electrons from NADH and FADH2 across the membrane Creates a proton gradient Oxygen is final electron acceptor

ATP production from gradient An ATP synthase in the inner mitochondrial membrane makes ATP ATP must be removed from mitochondrial matrix so proton gradient is in favor of ATP synthesis If proton flow is uncoupled from ATP synthase, energy is lost as heat

Fermentation Occurs in cell cytoplasm Reduces pyruvate and return NAD for use in glycolysis in the absence of oxygen Allows cell to produce small amounts of ATP Two types: lactic acid fermentation and alcoholic fermentation

Energy yields Aerobic yields 36 ATP Anaerobic yields 2 ATP