The next carrier, called cytochrome c oxidase, oxidizes cytochrome c by taking electrons from it. Cytochrome c reductase reduces the next carrier, cytochrome c, by donating electrons to it. In redox reactions, molecules that gain electrons are said to be reduced, while those that lose electrons are said to be oxidized. In turn, ubiquinone passes the electrons to cytochrome c reductase, a transfer that is coupled to the pumping of protons into the intermembrane space.Ĭytochrome c reductase derives its name from a redox reaction that it participates in. NADH-Q reductase then passes the electrons to a mobile molecule called ubiquinone. The electron transfer to the first carrier, called NADH-Q reductase, drives the protein complex to pump protons across the membrane. The respiratory chain is important in part because it regenerates NAD +, which is required in glycolysis and the citric acid cycle. When NADH donates electrons to the first carrier, NADH converts back to NAD +. The respiratory chain consists of a series of electron carriers, each of which holds donated electrons tighter and with greater affinity than the previous carrier in the chain. NADH molecules carry high-energy electrons that were removed from glucose during glycolysis and the citric acid cycle. NADH, along with FADH 2 (which is not shown), fuels the respiratory chain. The intermembrane space comes to be filled with protons pumped from the matrix by the action of the respiratory chain. The inner membrane contains the components required for electron transport (called the respiratory chain) and ATP synthesis. Most of this ATP is generated in mitochondria during the final phase of cellular respiration, during which electron transport and ATP synthesis take place.Ī mitochondrion has two membranes-an inner and an outer membrane-that divide the organelle into separate compartments. In glycolysis and cellular respiration, a cell breaks down a molecule of glucose and uses its energy to form 32 molecules of ATP, an important cellular energy source. In the accompanying animation, we focus on the respiratory chain, the final phase of cellular respiration, and the phase in which the cell makes the bulk of its ATP. Cellular respiration occurs in three main phases: pyruvate oxidation, the citric acid cycle, and the respiratory chain. Pyruvate then enters a mitochondrion, where cellular respiration occurs. In glycolysis, enzymes in the cytosol split glucose into two molecules of pyruvate. By the end of these pathways, glucose has been completely oxidized and the cell has gained 32 molecules of ATP-a versatile energy carrier that fuels most kinds of cellular work. It uses the energy that is released to form molecules of ATP, the energy-carrying molecules that cells use to power biochemical processes.Script Electron Transport and ATP Synthesis INTRODUCTIONĪn organism that lives in the presence of oxygen can extract a great deal of energy from glucose by running it through two main metabolic pathways: glycolysis and cellular respiration. This is because cellular respiration releases the energy in glucose slowly, in many small steps. The process is similar to burning, although it doesn’t produce light or intense heat as a campfire does. Heterotrophs depend on autotrophs, either directly or indirectly.Ĭellular respiration is the process by which individual cells break down food molecules, such as glucose and release energy. Humans are heterotrophs, as are all animals. Even if the food organism is another animal, this food traces its origins back to autotrophs and the process of photosynthesis. The Greek roots of the word heterotroph mean “other” ( hetero) “feeder” ( troph), meaning that their food comes from other organisms. Heterotrophs are organisms incapable of photosynthesis that must therefore obtain energy and carbon from food by consuming other organisms. Plants are also photoautotrophs, a type of autotroph that uses sunlight and carbon from carbon dioxide to synthesize chemical energy in the form of carbohydrates. Oceanic algae contribute enormous quantities of food and oxygen to global food chains. Plants are the best-known autotrophs, but others exist, including certain types of bacteria and algae. The Greek roots of the word autotroph mean “self” ( auto) “feeder” ( troph). An autotroph is an organism that can produce its own food. Some organisms can make their own food, whereas others cannot. When the covalent bond between the terminal phosphate group and the middle phosphate group breaks, energy is released which is used by the cells to do work. \): Chemical structure of ATP consists of a 5-carbon sugar (ribose) attached to a nitrogenous base (adenine) and three phosphates.
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