VITAMINShandouts - VITAMINS AND COENZYMES Structure and...

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VITAMINS AND COENZYMES Structure and functions
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Enzyme Cofactors
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Activator ions (loosely bound)
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Metal Ions as Cofactors Many active enzymes require a metal ion. Zn 2+, a cofactor for carboxypeptidase, stabilizes the carbonyl oxygen during the hydrolysis of a peptide bond.
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Some Enzymes and Their Cofactors
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Function of Coenzymes A coenzyme prepares the active site for catalytic activity.
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Coenzyme can also be classified by their source 1. Metabolite coenzymes : are synthesized from common metabolites e.g ATP, S-adenosylmethionine 1. Vitamin-derived coenzymes : are derivatives of vitamins, which are compounds that cannot be synthesized by animals and must be obtained as nutriens
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Metabolite Coenzymes Metabolite Coenzymes include a number of nucleoside triphosphates (ATP, GTP, CTP,UTP) Adenosine triphosphate (ATP) is by far the most abundant
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Adenosine triphosphate (ATP) ATP can donate : phosphoryl, pyrophosphoryl, adenyl (adenosine monophosphate =AMP), or adenosyl groups - in group transfer reactions.
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Cyclic Adenosine Monophosphate (cAMP)
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ATP is also the source of several other metabolite coenzyme One, S -adenosylmethionine , is synthesized by the reaction of methionine with ATP The positively charged sulfonium is highly reactive S -adenosylmethionine is the donor of virtually all the methyl groups used in biosynthetic reactions For example, it is required for the conversion of the hormone norepinephrine to epinephrine
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Vitamins and Vitamin-Derived Coenzymes Most vitamins are enzymatically transformed to their corresponding coenzymes
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Vitamins are classified into two groups by solubility: water- soluble and fat-soluble Water- soluble vitamins have polar groups such as -OH and -COOH, which make them soluble in the aqueous enviroment of the cells Fat-soluble vitamins are nonpolar compounds, which are soluble in the lipid components of the body (cell membrane, lipoproteins)
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Water-Soluble Vitamins Water-soluble vitamins are: Soluble in aque- ous solutions. Used as cofactors by many enzymes Not stored in the body.
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Thiamine (Vitamin B 1 ) Is part of the coenzyme thiamin pyrophosphate (TPP). TPP coenzyme is required by enzymes in the oxidative decarboxylation of α -keto carboxylic acids.
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Thiamine (Vitamin B 1 ) Deficiency results in beriberi (fatigue, weight loss, and nerve degeneration). Beriberi is caused by carbohydrate-rich/low thiamine diets, e.g. polished rice or other highly refined foods Wernicke-Korsakoff syndrome , a striking neuropsychiatric disorder is caused by lack thiamine in the diet. It is found frequently in chronic alcoholics consuming little other food.
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Riboflavin (Vitamin B 2 ) Riboflavin is: Part of the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN).
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