7.1 Cellular Respiration The ATP molecules that provide energy to eukaryotic cells are produced during cellular respiration. During cellular respiration, the mitochondria take in O 2 and release CO 2. Cellular respiration is the reason that animals breathe.
7.1 Cellular Respiration (cont.) Oxidation, the removal of hydrogen atoms from a molecule, is a central reaction in cellular respiration. reduction 6 CO H 2 O + energyC 6 H 12 O O 2 oxidation
7.1 Cellular Respiration (cont.) The breakdown of glucose during cellular respiration releases energy. The slow oxidation of glucose in the mitochondria allows the energy to be removed slowly and stored as ATP.
7.1 Cellular Respiration (cont.)
Phases of Complete Glucose Breakdown Cellular respiration involves a metabolic pathway of enzymes assisted by coenzymes. The two coenzymes involved in cellular respiration, NAD + and FAD +, receive the hydrogen atoms removed from glucose.
Phases of Complete Glucose Breakdown (cont.) The complete oxidation of glucose involves four phases. – Glycolysis, the splitting of glucose into two 3-carbon molecules –The preparatory reaction, which divides each 3- carbon molecules into a 2-carbon molecule and CO 2 –The citric acid cycle, which produces CO 2, NADH, FADH 2, and ATP –The electron transport chain, which assists in the production of the largest amount of ATP
Phases of Complete Glucose Breakdown (cont.)
7.2 Outside the Mitochondria: Glycolysis Glycolysis takes place in the cytoplasm of the cell. During glycolysis, glucose (a 6-carbon molecule) is broken down to two pyruvate (3-carbon) molecules. Glycolysis is divided into two stages. – Energy-Investment Steps – Energy-Harvesting Steps
7.2 Outside the Mitochondria: Glycolysis (cont.)
Energy-Investment Steps Some molecules must be energized before they can be broke down. To facilitate glucose breakdown during glycolysis, 2 ATP molecules energize glucose by donating their phosphate groups.
Energy-Harvesting Steps During the energy-harvesting steps, substrates are oxidized and the hydrogen atoms removed are used to form NADH. This oxidation also produces substrates with high-energy phosphate groups, which can be used to synthesize ATP. The transfer of a phosphate group from a molecule to form ATP is called substrate-level ATP synthesis.
Energy-Harvesting Steps (cont.) Glycolysis produces a total of four ATP. Since two ATP were used to initiate glycolysis, the net ATP production from glycolysis is two ATP. The metabolic fate of pyruvate, the product of glycolysis, depends upon the presence of oxygen.
Energy-Harvesting Steps (cont.)
7.3 Inside the Mitochondria The remaining stages of cellular respiration occur in the mitochondria. These steps require the presence of oxygen. The structural features of the mitochondria contribute to cellular respiration.
7.3 Inside the Mitochondria (cont.)
Preparatory Reaction The preparatory (prep) reaction of glycolysis, which occurs twice for each glucose molecule, produces the substrate that enters the subsequent citric acid cycle. Several events occur in the preparatory reaction. – Pyruvate is oxidized and releases a molecule of CO 2 and a 2-carbon acetyl group. –NAD + accepts a hydrogen atom, producing NADH. –The acetyl group is attached to coenzyme A (CoA) to form acetyl-CoA.
The Citric Acid Cycle The citric acid cycle occurs in the matrix of the mitochondria. Several events occur during the citric acid cycle. –The acetyl group is oxidized to CO 2. –Both NAD + and FAD + accept hydrogen atoms, forming NADH and FADH respectively. –Substrate-level ATP synthesis occurs, forming ATP. The citric acid cycle turns twice for each glucose molecule.
The Citric Acid Cycle (cont.)
The Electron Transport Chain The electron transport chain is located in the cristae of the mitochondria. The members of the electron transport chain accept electrons from the hydrogen atoms accepted by NADH and FADH 2. As the electrons are passed down the electron transport chain, energy is released and captured for ATP production.
The Electron Transport Chain (cont.) At the end of the electron transport chain, the electrons are donated to oxygen atoms to form water. The number of ATP molecules formed depends upon the electron donor. –The electrons from NADH provide energy for the synthesis of three ATP molecules. –The electrons from FADH 2 provide energy for the synthesis of two ATP molecules.
The Electron Transport Chain (cont.)
The Cristae of a Mitochondrion The members of the electron transport chain are imbedded in the cristae of the mitochondria in a specific pattern. As the members of the electron transport chain accept electrons from NADH and FADH 2, the H + are pumped into the intermembrane space.
The Cristae of a Mitochondrion (cont.) This pumping creates an H + reservoir in the intermembrane space. This reservoir can be released through an ATP synthase complex to synthesize ATP.
The Cristae of a Mitochondrion (cont.)
Energy Yield from Glucose Metabolism The complete breakdown of glucose yields 36 ATP molecules. –Glycolysis provides 2 net ATP. –The NADH produced by the prep reaction and the citric acid cycle yield 30 ATP. –The electron transport chain uses FADH 2 to produce 4 ATP.
Energy Yield from Glucose Metabolism (cont.)
Alternative Metabolic Pathways Cells can breakdown other molecules, such as lipids and proteins, to yield ATP. Lipids can be broken down to produce more ATP than glucose. –The glycerol from lipids enters cellular respiration at glycolysis. –The fatty acids from lipids can be metabolized into acetyl groups, which enter the citric acid cycle.
Alternative Metabolic Pathways (cont.) The hydrocarbon backbone of amino acids can enter cellular respiration at several points and can be broken down to produce energy. The small molecules produced during cellular respiration can be used to synthesize larger molecules.
Alternative Metabolic Pathways (cont.)
7.4 Fermentation Fermentation is the anaerobic breakdown of glucose, forming 2 ATP and a toxic by-product. In animal cells during fermentation, pyruvate from glycolysis is reduced to lactate, reforming NAD +. Although fermentation produces only 2 ATP molecules per glucose, it is essential as a quick source of ATP energy for cells.
7.4 Fermentation (cont.) When fermentation occurs in muscles during vigorous exercise, the lactate builds up, as does an oxygen deficit. The increase in lactate changes the pH, creating the “burn” associated with exercise.
7.4 Fermentation (cont.)
Microorganisms and Fermentation Bacterial fermentation produces either lactate or alcohol + CO 2. Yeast are well known microorganisms that produce alcohol and CO 2 during fermentation. –CO 2 production is what causes bread to rise. –Ethanol production is critical for the making of beer and wine.