Chapter07FALL05 - Chapter 7 - Coenzymes There are other...

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There are other groups that contribute to the reactivity of enzymes beside amino acid residues. These groups are called cofactors - chemicals required by apoenzymes (inactive) to become holoenzymes (active). There are two types of cofactors: 1) essential ions - metal ions -inorganic 2) coenzymes - organic molecules that act as group-transfer reagents (accept or donate groups)- can also be H + and/or e - Both provide reactive groups not found on a.a. side chains. Coenzymes can be either cosubstrates (loosely bound to enzyme; is altered, then regenerated) or prosthetic groups (tightly bound to enzyme). Coenzymes can be classified by their source: 1) metabolite coenzymes synthesized by common metabolites include nucleoside triphosphates most abundant is ATP, but also include uridine diphosphate glucose (UDP- glucose) and S-adenosylmethionine ATP can donate all of its three phosphoryl groups in group-transfer reactions S-adenosylmethionine can donate its methyl group in biosynthetic reactions. UDP-glucose is a source of glucose for synthesis of glycogen in animals and starch in plants. 2) vitamin-derived coenzymes Vitamins are required for coenzyme synthesis and must be supplied in the diet Lack of particular vitamins causes disease There are two catagories of vitamins: 1) water-soluble - B vitamins and vit. C required daily in diet excess excreted in urine 2) lipid-soluble - vitamins A, D, E, K Intake must be limited
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This note was uploaded on 08/02/2009 for the course BIOCHEMIST 100 taught by Professor Crew during the Spring '05 term at North Alabama.

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Chapter07FALL05 - Chapter 7 - Coenzymes There are other...

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