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
Digestion and Absorption of Folate
To be absorbed, folate must first be digested to its monoglutamate form (FGCP). It is moved into the cells by the proton-coupled folate transporter (PCFT).
Folate’s relationship to b6
x
Folate’s relationship to b12
x
SAM and Folate
Being deficient in either folate or b12 will reduce the available amounts of SAM
Assessment of nutritional status Folate
Concentration of folate is often tested in the plasma, serum, or red blood cells.
RDA as DFE Folate
RDA = 400 ug
Consequences of Folate Deficiency
Megaloblastic Anemia, diarrhea, fatigue, depression, confusion
Functions of B12
Responsible for Methylation of homocysteine to methionine;
Conversion of methylmalonyl CoA to succinyl CoA
B12 Deficiency disease and cause
Megaloblastic Anemia and degeneration of peripheral nerves.
DRI
Dietary Reference Intake
a system of nutrition recommendations from the Institute of Medicine (IOM) of the U.S. National Academy of Sciences. The DRI system is used by both the United States and Canada and is intended for the general public and health professionals.
RDA
Recommended Daily Allowance
the daily dietary intake level of a nutrient considered sufficient by the Food and Nutrition Board to meet the requirements of 97.5% of healthy individuals in each life-stage and sex group. It is calculated based on the EAR and is usually approximately 20% higher than the EAR
AI
Adequate Intake
where no RDA has been established, but the amount established is somewhat less firmly believed to be adequate for everyone in the demographic group.
UL
Tolerable Upper Limit
to caution against excessive intake of nutrients (like vitamin A) that can be harmful in large amounts. This is the highest level of daily consumption that current data have shown to cause no side effects in humans when used indefinitely without medical supervision.
Vitamin Classifications
Energy Releasing
Hematopoietic
Other
Thiamin’s role in Pentose and NADPH synthesis
Part of the Pentose Phosphate Pathway which is key in synthesis of Pentose and NADPH
Thiamin as TDP is a coenzyme in…
Pyruvate dehydrogenase complex, branched chain a-keto acid dehydrogenase complex, and the a-ketoglutarate dehydrogenase complex. Also needed for the Transketolase used in the Synthesis of NADPH
Energy Releasing B Vitamins
B1 Thiamin B2 Riboflavin B3 Niacin B5 Pantothenic Acid B6 B7 Biotin
Hematopoietic Vitamins
B5 Pantothenic Acid
B6
B12
Folate
EAR
Estimated Average Requirement
expected to satisfy the needs of 50% of the people in that age group based on a review of the scientific literature.
Main coenzyme form of riboflavin
FAD
Main coenzyme form of niacin
NAD
Thiamin as TDP is important for activity of which enzyme?
transketolase
What is needed to release biotin from proteins
Biotinidase
Niacin synthesis precursor
Tryptophan
Nutritional status of Riboflavin is measured by what enzyme
glutathione reductase
Essential for the function of B3
Biotin
Vitamins associated with Pyruvate dehydrogenase complex
Niacin, Pantothenic Acid, Riboflavin, Thiamin (TDP)
1, 2, 3, 5
