Exam 1 Flashcards
1. Function (enzymes, physiological, structural, etc.). 2. Mechanism of absorption (from the mouth, gi tract, to sites of storage and metabolic activity). 3. Factors that affect bioavailability and nutrient absorption (other dietary factors, medications). 4. Various chemical forms (metabolic action, bioavailability, food sources vs. supplement sources). 5. Food sources (rich sources, as well as the most common sources). 6. Recommended intakes throughout the lifecycle. 7. Time of lif
Functions and Structure of Thiamin
Structure: hex and a pent
Energy Transformation; Coenzyme role
Synthesis of Pentoses and NADPH; coenzyme role
Membrane and nerve conduction; non-coenzyme
Mechanism of absorption Thiamin
Thiamin is only absorbed in it’s phosphorylated forms (typically TDP and TPP, but also TMP and TTP) thanks to intestinal phosphatases. The Thiamin is hydrolyzed from the mono, di, and triphosphates leaving the free Thiamin to be absorbed into the intestinal cells.
Absorbed in the Jejunum and Ileum (also the duodenum to a lesser extent)
Factors Affecting Bio-availability Thiamin
Thiamin’s methylene bridge is very sensitive to both heat (high temp) and alkaline conditions (pH 8+).
Raw fish have thiaminases (which are rendered inactive by cooking)
Polyhydroxyphenols (found in coffee, nuts, and blueberries) inactivate thiamin by destroying the Thiazole ring
Various Chemical Forms Thiamin
Thiamin Mono, Di, and triphosphate
Thiamin Pyrophosphate
Food Sources Thiamin
Widely distributed in meats (95% in phosphorylated form) as well as grain products and legumes, but most Thiamin in the American diet comes from enriched sources (much like riboflavin and niacin).
Thiamin’s Role in Energy Transformation
Functions as a coenzyme necessary for the ocidative decarboxylation of pyruvate, a-ketoglutarate, and the three branched chain amino acids valine, isoleucine, and leucine. These reactions are all essential in ATP generation
Deficiency symptoms and diseases Thiamin
Beriberi, muscle weakness, anorexia, tachycardia, enlarged heart, edema
Assessing Nutritional Status Thiamin
Thiamin status can be assessed by measuring thiamin in the blood or urine and by measuring erythrocyte transketolase activity in hemolyzed whole blood.
Function Riboflavin
Riboflavin as Flavin mononucleotide (FMN) or Flavin adenine Dinucleotide (FAD) function as coenzymes for a variety of oxidative enzyme systems.
Functional Forms of Niacin
Nicotinic Acid and Nicotinamide
Niacin RDA calculations
mg of protein over 60
Functions of Pantothenic Acid
Functions in the body as a component in the synthesis of 4’-phosphopantetheine and CoA
Assessing Nutritional Status Niacin
Urinary metabolite measures as well as serum or red blood cell indicators.
Toxicity Niacin
Vasodilatory problems (too much blood flow) as well as gastrointestinal stress.
Deficiency Symptoms Niacin
Pellagra, diarrhea, dermatitis, mental confusion, or dementia
Mechanism of Biotin
Biotin bonds covalently to each of four carboxlyases. Catalyzed by holocarboxylase synthetase.
Digestion and Absorption of Biotin
After having been hydrolyzed by enzymatic digestion, biotin is absorbed nearly completely in the small intestine
Anti Biotin Factors
Those who consume large quantities of large eggs or pregnant women are susceptible to biotin deficiency
Functions of Biotin
CO2 transfer / Carboxylation reactions
Converts Pyruvate to oxaloacetate
Forms Malonyl CoA from Acetate (ACoA)
Converts Propionyl CoA to Methylmalonyl CoA
Functions of Pantothenic Acid
Acyl Transfer reactions
Functional forms of B6
Pyridoxine, pyridoxal, pyridoxamine
Functions of B6
Transamination and decarboxylation reactions
Assessment of Nutritional Status of B6
Plasma PLP concentrations are typically considered the best indicator. Urinary B6 along with 4-pyridoxic acid over several day have also been used.
Deficiency of B6
Dermatitis, glossitis, and convulsions
