metabolic processes

• Metabolic reactions are regulated in response to the cell’s needs.
• Cells require energy for three main types of activity: synthesizing large molecules like RNA, DNA and proteins, pumping molecules or ions across membranes by ATP, and moving things around within the cell.
• AlcD has greater affinity for methanol or ethanol and offers a better safety profile than ethanol.
• AlcD is approved by the FDA for poisoning and managing methanol poisoning.
• Metabolism is the sum of all the enzyme-catalysed reactions in a cell or organism.
• Anabolism includes processes that combine to build complex molecules from simpler ones, such as photosynthesis and protein synthesis.
• Catabolism includes processes that break down complex molecules into simpler ones, such as cellular respiration and digestion.
• Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
• Most chemical changes do not occur in one large jump, but in a sequence of small steps, forming a metabolic pathway.
• Most metabolic pathways involve a chain of reactions.
• Some metabolic pathways form a cycle rather than a chain, where the end product of one reaction is the reactant that starts the rest of the pathway.
• A metabolic cycle regenerates the starting product in the final step, such as the Krebbs and Calvin cycle.
• Activation energy is the energy required to reach the transition state and is used to break or weaken bonds in the substrate.
• Enzymes lower activation energy by breaking or weakening bonds in the substrate.
• The substrate binds to the enzyme’s active site.
• The active site is altered to reach the transition state.
• Due to the binding, bonds in the substrate become stressed and/or less stable.
• The binding of the substrate lowers the overall energy of the transition state, reducing activation energy and thereby reducing the amount of energy required for the reaction.
• Enzyme function can be restricted by the presence of inhibitors, which are molecules that deactivate enzyme activity either temporarily or permanently.
• Reversible enzyme inhibitors are used to control enzyme activity by interacting with the enzyme and the substrate or the end product.
• The build up of end product or lack of substrate serves to deactivate the enzyme.
• Inhibition can follow one of two models: competitive inhibitors block the substrate from binding to the enzyme’s active site, preventing formation of the enzyme-substrate complex.
• Competitive inhibitors are chemically similar to the substrate and the effect of a CI can be reduced by increasing substrate concentration.
• Noncompetitive inhibitors prevent binding by changing the shape of the enzyme’s active site, binding way from the active site and preventing the substrate from binding.
• Noncompetitive inhibitors are chemically different from the substrate and increasing the concentration of substrate has no effect on a NCI.
• The maximum rate of reaction is greatly reduced by the presence of the inhibitor.
• Examples of competitive inhibitors include the antibiotic prontosil, which inhibits the synthesis of folic acid in bacteria by binding to the active site of the enzyme dihydropteroate synthetase.
• Bacteria cannot replicate without folic acid, while animal cells are not affected because they absorb folic acid from food.
• Relenza is a synthetic drug used to treat influenza by inhibiting neuraminidase, a viral enzyme that cleaves a docking protein, preventing the release of virions and the spread of influenza virus.
• A virion is the complete, infective form of a virus outside a host cell with a core of RNA or DNA and a protein capsid.
• Cyanide binds away from the active site on cytochrome oxidase, a protein carrier molecule in the electron transport chain of mitochondria, inhibiting the enzyme and causing the electron transport chain to stop, preventing the production of ATP and leading to cell death in energy-dependent tissues such as cardiac muscle.
• Penicillin is an NCI that binds to the bacterial enzyme DD-transpeptidase, which catalyses the formation of peptidogylcan links in the bacterial cell wall, inhibiting the enzyme and causing the cell wall to not continuously strengthen, leading to its breakdown.
• Allosteric inhibitors are used to regulate metabolic pathways by binding to an allosteric site on the enzyme, inhibiting the enzyme and preventing the buildup of a product that is in excess or the buildup of intermediate products, allowing for an equilibrium position to be reached where there is a characteristic ratio of substrates and products.
• Threonine is converted into α-ketobutyrate, leading to the synthesis of isoleucine.
• The enzyme that catalyses this step, threonine deaminase, is inhibited by ISO and activated by valine, a product of a parallel pathway.
• ISO is an essential part of the human diet and is synthesized from another AA (threonine), accumulating in the cell and acting as an allosteric inhibitor of threonine deaminase, shutting down the pathway.
• Ethanol has been used to act as a competitive inhibitor for antifreeze poisoning (ethylene glycol).
• Fomepizole is an inhibitor of alcohol dehydrogenase and is also used for antifreeze poisoning.