13. Lock and Key Model Enzyme returns from the reaction unchanged and can now react with more substrate. enzyme S1 S2 S2 enzyme S1 ENZYME SUBSTRATE COMPLEX enzyme SUBSTRATE MOLECULES Active site P P Products
30. Most water-soluble vitamins are components of coenzymes Vitamin Coenzyme Deficiency Thiamine (B 1 ) Thiamine pyrophosphate Beriberi (weight loss,other problems Riboflavin (B 2 ) FAD + Mouth lesions, dermatitis Nicotinic acid (niacine) NAD + Pellagra (dermatitis, depression) Pantohtinic acid Coenzyme A Hypertension Biotin Biotin Rash, muscle pain
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32. Competitive inhibitors chemicals that resemble an enzyme’s normal substrate and compete with it for the active site . Substrate Enzyme Competitive inhibitor
33. Noncompetitive Inhibitors Inhibitors that do not enter the active site , but bind to another part of the enzyme causing the enzyme to change its shape , which in turn alters the active site . Substrate Enzyme active site altered Noncompetitive Inhibitor
49. Zymogen Pepsinogen Chymotrypsinogen Trypsinogen Procarboxypeptidase Proelastase Prothrombin Fibrinogen Factor VII Factor X Proinsulin Procollagen Procollagenase Active Enzyme Pepsin Chymotrypsin Trypsin Carboxypeptidase Elastase Thrombin Fibrin Factor VIIa Factor Xa Insulin Collagen Collagenase Function protein digestion protein digestion protein digestion protein digestion protein digestion blood clot formation blood clot formation blood clot formation blood clot formation plasma glucose homeostasis component of skin and bone remodeling processes during metamorphosis, etc.
60. Enzyme 1 Enzyme 2 Enzyme 3 Inter- mediate Inter- mediate X Product Start of pathway Presence of product inhibits enzyme 1 Feedback inhibition Many enzymes are actually regulated by the end products of the reaction they catalyze This prevents too much product from being made
61. An example of Feedback inhibition This example demonstrates how an end product can inhibit the first step in its production. Isoleucine binds to the allosteric site of threonine deaminase and prevents threonine from binding to the active site because the shape of the active site is altered. When the level of isoleucine drops in the cell’s cytoplasm, the isoleucine is removed from the allosteric site on the enzyme, the active site resumes the activated shape and the pathway is “cut back on” and isoleucine begins to be produced.
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Notas do Editor
This example demonstrates how an end product can inhibit the first step in its production. Isoleucine binds to the allosteric site of threonine deaminase and prevents threonine from binding to the active site because the shape of the active site is altered. When the level of isoleucine drops in the cell’s cytoplasm, the isoleucine is removed from the allosteric site on the enzyme, the active site resumes the activated shape and the pathway is “cut back on” and isoleucine begins to be produced.
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