Mitochondria, Respiration, and Photosynthesis: Energy Processes in Cells

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•Animals, plants, fungi, and most protists depend on mitochondria for energy to grow and survive

•There are more than 100 known mitochondrial disorders (including Luft syndrome)

•Defective mitochondria also contribute to many age-related problems (including Alzheimer’s)

•Aerobic respiration

•Form of cellular respiration in eukaryotes and many prokaryotes

•Oxygen is a reactant in the ATP producing process

•Anaerobic respiration

•Form of cellular respiration in some prokaryotes

•A molecule other than oxygen, such as sulfate or nitrate, is used in the ATP-producing process

•Photosynthesis stores energy from sunlight in electron-rich fuel molecules (such as sugars)

•Cellular respiration moves electrons from fuel to other molecules (such as oxygen) that act as electron acceptors

•Electron energy is used to drive ATP synthesis


•The removal of electrons from a substance

•The substance from which the electrons are removed (the electron donor) is oxidized


•The addition of electrons to a substance

•The substance that receives the electrons (the electron acceptor) is reduced

•Oxidation and reduction reactions are always coupled

•Redox reactions

•Reactions that remove electrons from a donor molecule and simultaneously add them to an acceptor molecule

•During photosynthesis, electrons from water are pushed to very high energy levels and stored (along with H+) in sugar molecule

•Cellular respiration releases energy from electrons as they pass among acceptor molecules to a final acceptor (oxygen

•Total energy obtained depends on the difference between the high energy level in fuel and the lower energy level in the final acceptor


•Enzymes break a 6-carbon molecule of glucose into two 3-carbon molecules of pyruvate

•Some ATP is synthesized by substrate-level phosphorylation – an enzyme-catalyzed reaction that transfers a phosphate group from a substrate to ADP

•Pyruvate oxidation

•Enzymes convert the 3-carbon pyruvate into a 2-carbon acetyl group, which enters the citric acid cycle and is completely oxidized to carbon dioxide

•Some ATP is synthesized during the citric acid cycle

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