* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Carbohydrate Catabolism in the Presence of Oxygen Releases a
Butyric acid wikipedia , lookup
Amino acid synthesis wikipedia , lookup
Magnesium in biology wikipedia , lookup
Biosynthesis wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Fatty acid metabolism wikipedia , lookup
Metalloprotein wikipedia , lookup
Phosphorylation wikipedia , lookup
Photosynthesis wikipedia , lookup
Mitochondrion wikipedia , lookup
Nicotinamide adenine dinucleotide wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
NADH:ubiquinone oxidoreductase (H+-translocating) wikipedia , lookup
Biochemistry wikipedia , lookup
Light-dependent reactions wikipedia , lookup
Electron transport chain wikipedia , lookup
Microbial metabolism wikipedia , lookup
Adenosine triphosphate wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
6.2 Cellular respiration: the set of metabolic reactions used by cells to harvest energy from food A lot of energy is released when reduced molecules with many C—C and C—H bonds are fully oxidized to CO2. The oxidation occurs in a series of small steps, allowing the cell to harvest about 34% of the energy released. Catabolism of glucose under aerobic conditions (in the presence of O2), occurs in three linked biochemical pathways: Glycolysis—glucose is converted to pyruvate. Pyruvate oxidation—pyruvate is oxidized to acetyl CoA and CO2. Citric acid cycle—acetyl CoA is oxidized to CO2. Glycolysis Ten reactions Takes place in the cytosol Final products: 2 molecules of pyruvate (pyruvic acid) 2 molecules of ATP 2 molecules of NADH Steps 6 and 7 are examples of reactions that occur repeatedly in metabolic pathways: Oxidation–reduction (step 6): exergonic; glyceraldehyde 3- phosphate is oxidized and energy is trapped via reduction of NAD+ to NADH. Substrate-level phosphorylation (step 7): also exergonic; energy released transfers a phosphate from 1,3-bisphosphoglycerate to ADP, forming ATP. Pyruvate Oxidation Occurs in mitochondria in eukaryotes. Products: CO2 and acetate; acetate is then bound to coenzyme A (CoA) to form acetyl CoA. NAD+ is reduced to NADH. Citric Acid Cycle Eight reactions Occurs in mitochondria in eukaryotes Operates twice for every glucose molecule that enters glycolysis Starts with Acetyl CoA; acetyl group is oxidized to two CO2 Oxaloacetate is regenerated in the last step Final reaction of citric acid cycle: Cells transfer energy from NADH and FADH2 to ATP by oxidative phosphorylation: NADH oxidation is used to actively transport protons (H+) across the inner mitochondrial membrane, resulting in a proton gradient. Diffusion of protons back across the membrane then drives the synthesis of ATP. When NADH is reoxidized to NAD+, O2 is reduced to H2O: NADH + H+ + ½ O2 ® NAD+ + H2O This occurs in a series of redox electron carriers, called the respiratory chain, embedded in the inner membrane of the mitochondrion. Electron transport: electrons from the oxidation of NADH and FADH2 pass from one carrier to the next in the chain. The oxidation reactions are exergonic, energy released is used to actively transport H+ ions across the membrane. Oxidation is always coupled with reduction. When NADH is oxidized to NAD+, the reduction reaction is the formation of water from O2. 2 H+ + 2 e– + ½ O2 ®H O 2 The key role of O2 in cells is to act as an electron acceptor and become reduced. ATP synthase uses the H+ gradient to drive synthesis of ATP by chemiosmosis: Chemiosmosis: Movement of ions across a semipermeable barrier from a region of higher concentration to a region of lower concentration. ATP synthase converts the potential energy of the proton gradient into chemical energy in ATP. ATP synthase is a molecular motor with two subunits: F0 is a transmembrane domain that functions as the H+ channel. F1 has six subunits. As protons pass through F0, it rotates, causing part of the F1 unit to rotate. ADP and Pi bind to active sites that become exposed on the F1 unit as it rotates, and ATP is made. ATP synthase structure is similar in all organisms. In prokaryotes, the proton gradient is set up across the cell membrane. In eukaryotes, chemiosmosis occurs in mitochondria and chloroplasts. The mechanism of chemiosmosis is similar in almost all forms of life. Chemiosmosis can be demonstrated experimentally. A proton gradient can be introduced artificially in chloroplasts or mitochondria in a test tube. ATP is synthesized if ATP synthase, ADP, and inorganic phosphate are present. About 32 molecules of ATP are produced for each fully oxidized glucose. The role of O2: most of the ATP is formed by oxidative phosphorylation, which is due to the reoxidation of NADH. Some bacteria and archaea use other electron acceptors. Geobacter metallireducens can use iron (Fe3+) or uranium, making it potentially useful in environmental cleanup.