Enzymes o one of the most important types of proteins

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Enzymes o One of the most important types of proteins in our cells. o Known as catalysts, they speed up reactions and use less energy ↑rate of reaction, ↓activation energy Can do the same reaction over and over They only act on specific substrates - a molecule that is specific for that enzyme Binds via its active site , a binding platform for its specific substrate Have a high degree of specificity - they catalyze only one type of reaction, and most act on only one substrate Molecules that are different in shape or function bind to the enzyme. Therefore, the enzyme and its substrate are complementary, like a “lock and key”. While an enzyme and its substrate are complementary, many enzymes will adjust their active site slightly to improve the fit of the substrate. Known as induced fit, “hug”. o Reusable- Enzyme cycle Enzyme + specific molecule/induced fit = reaction/product, then release of product Enzyme pathways o Enzyme reaction: substrate + enzyme = product o Enzyme pathway: Substrate + enzyme 1 = product Enzyme 1 product (now substrate) + enzyme 2 = enzyme 3 The product of one enzyme can be the substrate of another. o Control of enzyme activity An organism must be able to control its enzyme availability and activity. 1. Control of enzyme availability- depends on its rate of synthesis and degeneration. Changes over time. 2. Control of enzyme activity- can be inhibited due to too much product or presence of inhibitors, and can be modulated (modified) through structural alterations. o Control by modification: phosphorylation and dephosphorylation (attachment/removal of a phosphate group) Page 19 of 41
o Control by enzyme inhibition: Feedback inhibition – similar to the drug induced form of noncompetitive inhibition, when excess product is detected, the pathway is stopped by inhibition. The product at the end of the pathway binds to allosteric site on the first enzyme at the beginning of the pathway to stop the process. o Medical inhibition with drugs Competitive inhibition - appears similar to the substrate, binds to the active site on the enzyme to prevent substrate from binding Can be overcome by adding additional substrate, if there’s too much substrate and not enough inhibition the substrate will win. Noncompetitive inhibition - binds to the allosteric site (away from the active site) Changes shape of protein and therefore changes the active site, causing the substrate to not be able to fit into the enzyme. Page 20 of 41
Biochem Mod 3 Myoglobin and Hemoglobin o Myoglobin- storage of oxygen, holds onto it 1 subunit, one polypeptide chain with tertiary structure , has only one heme therefore can only carry one oxygen molecule Can grab oxygen quickly, stores oxygen within muscles tightly (high affinity ) Is not affected by changes in pH Since it is stored in muscles, can be used to detect MI, rhabdomyolysis, etc. because it will be released when muscle is damaged. o Hemoglobin- transport of oxygen 4 subunits, quaternary structure

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