Ex.6 - Micronutrients (59-60)

Question 1

Daily values

Answer 1

Determined by FDA for a daily diet of 2,000 calories a day
-Originally based on RDA in 1968

Question 2

Dietary reference intakes

Answer 2

System of nutrition recommendations from the institute of medicine of the National Academies
-Dietary reference intakes: Guiding principles for nutrition labeling and Fortification (2003)
-Replaced original recommended dietary allowance (RDA)
-Provides several different types of reference values:
-Estimated average requirement (EAR)
-Recommended dietary allowance (RDA)
-Adequate intake (AI)
Tolerable upper intake levels: (UL)

Question 3

Dietary reference intakes explained

Answer 3

Estimated average requirement (EAR)
-The amount of nutrient estimated to meet the need of 50% of the healthy individuals in an age and gender group

Recommended dietary allowance (RDA)
-Two standard deviations above the EAR
-Sufficient to meet the need of nearly all (97-98%) healthy individuals in a group

Adequate intake (AI)
-Used when scientific evidence is inadequate to set an EAR
-Approximations of the average nutrient intake by a healthy population

Tolerable upper intake level (UL)
-The max level of daily intake of a nutrient w/o any health risk

Question 4

Micronutrients

Answer 4

Vitamins:
Fat-soluble: Vitamin A, Vitamin D, Vitamin E, Vitamin K
Water soluble: group of vitamin’s B and C

Minerals;
Macrominerals: Ca2+ and Mg2+
Trace minerals: iron, iodine, zinc, copper, selenium chromium, manganese, molybdenum, fluoride, boron

Question 5

Vitamins

Answer 5

Organic compounds that are essential in the diet to promote and regulate body function

When insufficient in diet, deficiency symptoms occur

Named alphabetically in the order of their discovery:
-B vitamins were initially thought to be one chemical substance
-Only B6 and B12 are referred to by the numbers

Grouped into fat and water soluble vitamins
-Each group shares similar absorption, excretion, and storage properties

Question 6

Vitamins and names

Answer 6

B1 - thiamin
B2 - Riboflavin
B3 - Niacin
B5 - Panthoenic acid
B6 - Pyridoxine
B7 - Biotin
B9 - Folic acid
B12 - Cobalamin

Question 7

Vitamin A

Answer 7

Retinol, retinal and retinoic acid

Produced from Carotenoids, organic pigments in plants
Cis-retinal reversibly associates with opsins and function as light sensor
-Vitamin A deficiency may cause night blindness

Question 8

Vitamin A - Retinoic Acid

Answer 8

Retinoic acid function as hormones, regulating cell growth, and differentiation

-Associates with nuclear receptors: Retinoic acid receptors (RARs) and retinoid X receptors (RXR)

-Carotenoids are effective antioxidants; may reduce the risk of cancers

-Stored in the liver as retinol palmitate

-Dietary sources: dark green and yellow vegetables, liver, egg yolk, butter, and whole milk

Deficiency is rare, but
40-60% of Americans Consume less than 2/3 of RDA

Question 9

Vitamin D

Answer 9

Function as steroid hormones maintaining calcium homeostasis

Synthesized from an intermediate in cholesterol biosynthesis

Produced photochemically in the skin

Insufficient exposure to sunlight may cause vitamin D deficiency
-Rickets in young children and osteomalacia in adults

-Dietary sources: Vitamin D milk, saltwater, fish, liver and egg yolk

Question 10

Vitamin E

Answer 10

Occurs in diet as tocopherols and tocotrienols

Naturally occurring antioxidants protecting unsat fatty acids

Accumulate in circulating lipoproteins, cell membranes, and fat deposits

Reduce the risk of CV disease by preventing oxidation of LDL
-The oxidized form of LDL is atherogenic

Dietary sources: Vegetable oils rich in polyunsaturated fatty acids

Deficiency is rare

Question 11

Vitamin K

Answer 11

Carboxyglutamic acid residues allow proteins to bind Ca2+
-Essential for blood clotting
-Several proteins involved in blood coagulation require y-carboxyglutamic acid residues for Ca2+ binding (ex. Prothrombin)

Essential for bone mineralization
-Several proteins in bone require y-carboxyglutamic acid residues for binding to hydroxyapatatite (Osteocalcin)

Question 12

Vitamin K cont

Answer 12

In the carboxylation rxn, Vitamin K is converted to an inactive epoxide for m

Regeneration of the active form REQUIRES vitamin K epoxide reductase

Warfarin
-Anticoagulant, vitamin K antagonist
-Prevent thrombosis
-Inhibits K epoxide reductase

Dietary sources:
-Vitamin K1 in green vegetables
-Vitamin K2 synthesized by intestinal bacteria

deficiency is rare

Question 13

Thiamin - B1

Answer 13

Thiamin pyrophosphate - functions as a cofactor in enzymatic catalysis
-Thiazole ring forms carbanion, a strong nucleophile
-ex: pyruvate dehydrogenase, (Pyruvate-> acetyl CoA)

thiamin Triphosphate - function in transmission of nerve impulse in peripheral nerve membranes

Severe thiamin deficiency is known as beriberi
-Characterized by muscular atrophy and weakness
-May occur in populations exclusively relying on polished rice for food or in alcoholics

Question 14

Riboflavin (B2)

Answer 14

Precursor of cofactors used in many redox rxns
-Flavin adenine dinucleotide (FAD)
Flavin mononucleotide (FMN)

Riboflavin deficiency is very rare
-Symptoms; angular cheilitis, glossitis, and scaly dermatitis
Usually seen in chronic alcoholics

Rich in milk, meat, eggs, and cereal products

Question 15

Niacin - B3

Answer 15

niacin (nicotinic acid) and Niacinamide (nicotinamide) in diet
Converted to cofactors, NAD and NADP
-Electron acceptors or hydrogen donors
-Essential in many redox rxns and cellular respiration
-NAD is also used for ADP-ribosylation

Severe deficiency is known as pellagra
-Dermatitis, diarrhea, and dementia
Rare: Primarily seen in alcoholics, patients w/severe malabsorption, and elderly on very restricted diets

Rich in meats, peanuts, and enriched cereals

Question 16

Pyridoxine (B6)

Answer 16

Pyridoxine, Pyridoxamine and pyridoxal in diet

Converted to a cofactor, pyridoxal phosphate
-Synthesis of neurotransmitters
-Synthesis of sphingolipids

Deficiency:
-Mild: Irritability, nervousness, and depression
-Severe: Peripheral, neuropathy and convulsions

Rich in meat, vegetables and whole-grain cereals

A significant fraction of US population consumes less than recommended intake

Question 17

Biotin (B7)

Answer 17

Serves as a cofactor for activation of carbon dioxide in carboxylase enzymes
-Ex: Acetyl-CoA carboxylase (aacetyl-CoA-> malonyl-CoA)

Covalently bound to lysine side chains in enzymes

Rich in a wide range of food sources
Deficiency is rare
-May occur when raw egg white is consumed regularly; avidin in egg white forms a tight complex with biotin
_Common in pregnant women

Question 18

Folic acid (B9)

Answer 18

Converted to tetrahydrofolate a one-carbon carrier in enzyme rxns

Used in synthesis of Amino acids and nucleotides

Essential for DNA synthesis and cellular proliferation

Rich in a wide range of food sources

Deficiency inhibits DNA synthesis
-Produces abnormal red blood cells - anemia
-Increases the risk of birth defects, especially neural tube defect
-Common in alcoholics

Question 19

Cobalamin (B12)

Answer 19

Contains Co in a coordination state of six

Exists as a complex w/proteins

Required for two rxns in human
-Methionine synthase (homocysteine -> methionine
-Methymalyonyl-CoA-> succinyl-CoA)

When insufficient, homocysteine and methylmalonic acid accumulate, which causes anemia and neurological damage

Deficiency is rare except in patients with severe malabsorption diseases and long-term vegetarians

Question 20

Vitamin C

Answer 20

Ascorbic Acid

Functions as a cofactor for several oxidases
-Required for hydroxylation of lysine and proline side chains, which is necessary for collagen stability
-Proper collagen stability is essential for maintenance of normal connective tissue, wound healing ,and bone formation

Nonenzymatic reducing agent
-Aids in absorption of iron by reducing it to Fe2+ in the stomach
-Protects vitamin A, vitamin E, and some B vitamins from oxidation

Question 21

Vitamin C deficiency

Answer 21

Capillary fragility (mild)
-Easy bruising
-Decreased immunocompetence

Scurvy (severe)
-Decreased wound healing
-Osteoporosis
-Hemorrhaging
-Anemia

Smokers require more vitamin C
The use of megadoses of vitamin C to prevent and to cure common cold is controversial

Question 22

Calcium

Answer 22

Most abundant mineral in the body
-Makes bones
-Serves as a second messenger
-Required for many enzymes
-Essential for blood coagulation and muscle contractility

Maintenance of constant serum level is vital
-Elaborate homeostatic control system
-Bones serve as reservoir
-Dietary insufficiency results in net loss of Ca2+ from the bones
-Vitamin D is required for optimal utilization of Ca2+
-Exercise facilitates Ca2+ utilization for bone formation

Question 23

Calcium continued

Answer 23

Symptoms of Ca2+ deficiency resembles vitamin D deficiency

May contribute to osteoporosis
-Achieving max bone density from age 10-35 critical in reducing risk of osteoporosis later
-Proper calcium intake from the diet and exercise maximizes bone density

Mild deficiency may cause muscle cramps
-Significant portion of low income children and adult females do not get adequate Ca2+

Dietary sources:
-Dairy products
Nuts, beans, seeds, and seaweeds

Question 24

Iron

Answer 24

Required for O2 transport, energy metabolism, cell proliferation and immune defense

Blood loss including menstruation increases need
-Need 2 fold more than adult males

Iron homeostasis = tightly regulated
-Essential for life but also extremely toxic
-Free iron generates free radicals
-Normally sequestered in the cell by ferritin and in the blood by transferrin
-Iron deficiency anemia is widespread in children and menstruating females

Question 25

Trace minerals- Iodine

Answer 25

Used for synthesis of thyroid hormones
The best natural food source is seafood
Deficiency was endemic in inland populations
-Goiter
-Cretinism
Routinely added to table salt

Question 26

Trace minerals- Zinc

Answer 26

Required for many mealloenzymes and zinc finger proteins
-Deficiency in children results in poor growth and impairment of sex development
Deficiency may cause poor wound healing, dermatitis, and impaired immune function
-Zinc intake may be marginal for many individuals

Question 27

Trace minerals- Copper

Answer 27

Required for many enzymes
Ex- Lysyl oxidase, necessary for collagen cross linking
-Deficiency may cause anemia, bone demineralization, and blood vessel fragility

Question 28

Trace minerals - Selenium

Answer 28

Incorporated into ~25 selenoproteins in humans

Contain Selenocysteine residues, which are incorporated during translation

Selenocystyl-tRNA binds to UGA codons in MRNA with a special sequence in 3’ -untranslated region

Deficiency is rare