MTCC 117 LESSON 3.2 - VITAMINS.pdf

Lesson 3.2: Vitamins MTCC117 MTCC 117: BIOCHEMISTRY FOR MEDICAL LABORATORY SCIENCE SY 2024-2025...

Lesson 3.2: Vitamins MTCC117 MTCC 117: BIOCHEMISTRY FOR MEDICAL LABORATORY SCIENCE SY 2024-2025 1ST SEMESTER EFREN II C. DEOCADES, RMT, MSMT Less likely to be toxic More likely to be toxic OUTLINE unless taken in large when consumed in excess. I General Characteristics of Vitamins amounts. II Water-Soluble Vitamins Act as coenzymes for Generally do not function A Vitamin C various biochemical as coenzymes in humans B The B Vitamins reactions in humans, and animals and are rarely III Fat-Soluble Vitamins animals, and utilized by microorganisms. microorganisms. GENERAL CHARACTERISTICS OF VITAMINS Polar, easily absorbed. Dissolved in lipid materials. Water-soluble vitamins are Fat-soluble vitamins are VITAMINS polar, and can be easily dissolved in lipid materials. absorbed. ➔ Many enzymes contain vitamins as part of their structure ➔ Vitamins, in many cases, are cofactors in conjugated enzymes ➔ Vitamins are organic compounds essential in small amounts for proper human body functioning, obtained from dietary sources since the body cannot synthesize them. ➔ The term "vitamin" was originally "vitamine," derived from the Latin "vita" (meaning "life"), based on the belief that all these substances contained an amine functional group. ➔ Vitamins are needed in microgram to milligram quantities per day, differing from major nutrients like carbohydrates, lipids, and proteins ✓ A well-balanced diet typically meets the body's vitamin requirements, but supplements may be needed for pregnant women and individuals recovering from illnesses ✓ Some vitamins contain amine functional groups, but others do not. ✓ All vitamins, except vitamin D, can be sourced from diet ➔ Synthetic vitamins, manufactured in the WATER-SOLUBLE VITAMINS laboratory, are identical to the vitamins found in VITAMIN C foods. The body cannot tell the difference and gets the same benefits from either source. ➔ Vitamin C, which has the simplest structure of ➔ There are 13 known vitamins the 13 vitamins, exists in two active forms in the human body: an oxidized form and a reduced Vitamins are divided into two classes based on solubility: form. ➔ This simple compound can be made from WATER-SOLUBLE VITAMINS FAT-SOLUBLE VITAMINS glucose derivatives by all plants and most Must be constantly Stored in fat tissues, animals replenished due to rapid periodic doses needed. ➔ Humans, monkeys, apes, and guinea pigs are elimination via urine. among the relatively few species that require Carried in the bloodstream, Carried by protein carriers dietary sources of vitamin C. required in frequent small in the blood. ➔ Other species synthesize vitamin C from doses, and less likely to be carbohydrates toxic unless taken in large amounts. Frequent small doses More likely to be toxic in excess. MTCC 117 CANLAS, F. 1  LESSON 3.2: VITAMINS BIOSYNTHESIS OF VITAMIN C THE B VITAMINS (VITAMIN B COMPLEX) ➔ Vitamin B-containing coenzymes serve as 1) The biosynthesis of vitamin C starts with L-gulonic temporary carriers of atoms or functional acid, derived from the sugar L-gulose. groups in redox and group transfer reactions 2) An enzyme, lactonase, converts L-gulonic acid associated with the metabolism of ingested into a cyclic ester (lactone) by forming a ring food in order to obtain energy from the food between carbons 1 and 4. ➔ In their function as coenzymes, B vitamins usually 3) Then, an oxidase enzyme adds a double bond to do not remain permanently bonded to the the ring, forming L-ascorbic acid, which is vitamin apoenzyme that they are associated with C. └ They can be repeatedly used by various enzymes. This reuse (recycling) diminishes ➔ Its chemical name, L-ascorbic acid, correctly the need for large amounts of the B vitamins indicates that vitamin C is a weak acid in biochemical systems ➔ In human beings, an intake of 100 mg/day ➔ All of the B vitamins serve as precursors for saturates all body tissues with the compound enzyme cofactors. ➔ After tissue saturation, excess is excreted in the  Vitamin C is not an enzyme cofactor precursor urine Recommended daily intake varies by country: 30 mg/day (Great Britain) 60 mg/day (US/Canada) 75 mg/day (Germany)  Fruits and vegetables are rich in vitamin C FUNCTIONS OF VITAMIN C VITAMIN CHEMICAL NAME COLLAGEN SYNTHESIS B1 Thiamin ➔ Vitamin C function as a cosubstrate in the B2 Riboflavin formation of the structural protein collagen B3 Nicotinic acid, nicotinamide └ Vitamin C plays a key role in the formation of B5 Pantothenic acid collagen, essential for skin, ligaments, B6 Pyridoxine, pyridoxal, pyridoxamine tendons, bone, and teeth structure. B7 Biotin ➔ Vitamin C is needed for the synthesis of B9 Folic acid Hydroxyproline and Hydroxylysine, which help B12 Cobalamin bind collagen fibers, working alongside iron. └ Iron serves as a cofactor in the reaction ➔ The substance originally identified as vitamin B4 ➔ Vitamin C maintains iron in its functional state was later found to be adenine and acts as an antioxidant for water-soluble ➔ Vitamin B8 was found to be adenylic acid substances in the body. ➔ The structural forms of B vitamins found in food are not the same forms used by the GENERAL ANTIOXIDANT human body. ➔ B vitamins act as precursors for enzyme ➔ It acts as a general antioxidant by “recharging” cofactors, which are their active forms. spent enzymes that contain metal atoms ➔ After being obtained from food, B vitamins are ➔ It regenerates the active form of vitamin E and converted to their enzyme cofactor forms during helps maintain folate (a B vitamin) in its digestion. reduced state. ➔ The focus is on the chemical changes that occur ➔ Vitamin C has the ability to facilitate this change as "free" B vitamins are transformed into their by donating electrons to the iron-containing active enzyme cofactor forms within the body. enzyme SYNTHESIS OF NEUROTRANSMITTERS ➔ Dopamine and norepinephrine from tyrosine and serotonin from tryptophan depend on the presence of vitamin C ➔ The adrenal glands contain the highest levels of vitamin C. MTCC 117 CANLAS, F. C. 2  LESSON 3.2: VITAMINS THIAMIN (VITAMIN B1) VITAMIN B6 (PYRIDOXINE, PYRIDOXAL, AND PYRIDOXAMINE) ➔ The name thiamin comes from “thio,” which ➔ Vitamin B6 is a collective term for three related means “sulfur” and “amine” which refers to the compounds: pyridoxine (found in foods of plant numerous amine groups present origin) and pyridoxal and pyridoxamine (found in ➔ The coenzyme form of thiamin is called thiamin foods of animal origin). pyrophosphate (TPP) ➔ Vitamin B6 coenzymes participate in reactions ➔ The coenzyme TPP functions in the where amino groups are transferred between decarboxylation of a-keto acids molecules. Such transfer occurs repeatedly when protein molecules are metabolized. RIBOFLAVIN (VITAMIN B2) BIOTIN (VITAMIN B7) ➔ Riboflavin was once called the “yellow vitamin” because of its color. ➔ Biotin is unique among the B vitamins in that it └ Its name comes from its color (flavin means can be obtained both from dietary intake and “yellow” in Latin) and its ribose component. also via biotin-producing bacteria (microbiota, ➔ Two important riboflavin-based coenzymes exist: hence the name biotin) present in the human large flavin adenine dinucleotide (FAD) and flavin intestine. mononucleotide (FMN). ➔ “Free” biotin is biologically active. ➔ Both coenzymes are involved with oxidation- ➔ The coenzyme form of biotin is formed by the reduction reactions in which hydrogen atoms are carboxyl group of biotin’s pentanoic acid transferred from one molecule to another. attachment forming an amide linkage with a residue of the amino acid lysine present at the NIACIN (VITAMIN B3) enzyme’s active site. ➔ As a coenzyme, biotin participates in ➔ Niacin occurs in food in two different, but similar, carboxylation reactions. forms: nicotinic acid and nicotinamide. ➔ Both forms convert to the same coenzymes: FOLATE (VITAMIN B9) nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate ➔ Several forms of folate are found in foods. (NADP+) ➔ Both coenzymes are involved with oxidation- All of them have structures that consist of three parts: reduction reactions in which hydrogen atoms are transferred from one molecule to another 1) A nitrogen-containing double-ring system  It was prepared by oxidizing nicotine using nitric (pteridine) acid; hence the name nicotinic acid. 2) Paraaminobenzoic acid (PABA) and 3) One or more residues of the amino acid glutamate ➔ When only one glutamate residue is present, PANTOTHENIC ACID (VITAMIN B5) the folate is called folic acid. ➔ In food, about 90% of the folate molecules have ➔ The name pantothenic acid is based on the Greek three or more glutamate residues present; such word “pantothen,” which means “from molecules are called polyglutamates everywhere.” ➔ The active coenzyme form of folate, which is ➔ This vitamin is found in almost every plant and known as tetrahydrofolate (THF), has only one animal tissue. glutamate ➔ Coenzyme A (CoA), one of the most used of all ➔ THF is needed in methylation reactions vitamin B coenzymes, contains pantothenic acid ➔ The name folate comes from the Latin word as part of its structure “folium,” which means “leaf.” └ Coenzyme A is required in the metabolism of ➔ Dark green leafy vegetables are the best natural carbohydrates, lipids, and proteins, where it is source for folate involved in the transfer of acetyl groups between molecules. VITAMIN B12 (COBALAMIN) ➔ Acyl carrier protein (ACP), which may be regarded as a “giant coenzyme A molecule.” ➔ The name cobalamin comes from the fact that an └ ACP is important in the biosynthesis of fatty atom of the metal cobalt and numerous amine acids groups are present in the structure of vitamin B12 ➔ Most complex of all vitamin structures ➔ It is the only vitamin that contains a metal atom ➔ The free form is cyanocobalamin, and the coenzyme form is methylcobalamin MTCC 117 CANLAS, F. C. 3  LESSON 3.2: VITAMINS ➔ B12 coenzymes participate in the transfer of └ The body can synthesize retinol from retinal alkyl groups and hydrogen atoms from one in a reaction that is reversible; retinal can also molecule to another be converted to retinoic acid in an ➔ Only microorganisms can produce it; it cannot be irreversible reaction. made by plants, animals, birds, or humans └ Retinoic acid cannot be converted to either retinol or retinal ➔ Beta-carotene can be cleaved to yield 2 molecules of retinal, which can then be converted to retinol ➔ Beta-carotene is a yellow to red-orange pigment plentiful in carrots, squash, cantaloupe, apricots, and other yellow vegetables and fruits, as well as in leafy green vegetables (where the yellow pigment is masked by green chlorophyll). 4 MAJOR FUNCTIONS OF VITAMIN A Function Description Forms rhodopsin, a visual pigment involved in light-to- nerve impulse conversion. VITAMIN FUNCTION Participates in the Thiamin (B1) Decarboxylation of α-keto acids Vision conversion of light energy Riboflavin (B2) Oxidation-reduction reactions into nerve impulses. involving hydrogen transfer Only 0.1% of the body's Niacin (B3) Oxidation-reduction reactions vitamin A is found in the involving hydrogen transfer eyes. Pantothenic Metabolism of carbohydrates, Regulates the process of Acid (B5) lipids, and proteins (acetyl group immature cells becoming transfer) Regulating Cell specialized cells. Vitamin B6 Amino acid metabolism (amino Differentiation Retinoic acid binds to group transfer) protein receptors and DNA Biotin (B7) Carboxylation reactions molecules. Folate (B9) Methylation reactions Maintains the health of skin Vitamin B12 Transfer of alkyl groups and and internal linings. (Cobalamin) hydrogen atoms Prevents dryness and Epithelial hardening. Tissue Health Involves cellular FAT-SOLUBLE VITAMINS differentiation of mucus- secreting cells. ➔ Many of the functions of the fat-soluble vitamins Participates in sperm involve processes that occur in cell development in men. membranes Reproduction Essential for normal fetal ➔ The structures of the fat-soluble vitamins are and Growth development in women. more hydrocarbon-like, with fewer functional Involves cellular groups than the water-soluble vitamins differentiation processes. ➔ Their structures as a whole are nonpolar, which enhances their solubility in cell membranes VITAMIN D VITAMIN A The two most important members of the vitamin D family ➔ Normal dietary intake provides a person with of molecules are: both preformed and precursor forms (provitamin forms) of vitamin A. 1) Vitamin D3 (cholecalciferol) ➔ Preformed vitamin A forms are called retinoids. 2) Vitamin D2 (ergocalciferol). └ The retinoids include retinal, retinol, and retinoic acid. MTCC 117 CANLAS, F. C. 4  LESSON 3.2: VITAMINS ➔ Vitamin D3 is produced in the skin of humans Mechanism: and animals by the action of sunlight (ultraviolet light) on its precursor molecule, the cholesterol  Donates hydrogen atom to oxygen-containing free derivative 7-dehydrocholesterol (a normal radicals (reactive oxygen species). metabolite of cholesterol found in the skin)  Restored by vitamin C, forming a recycling system. ✓ Vitamin D2 is found in plants LOCATION OF VITAMIN E ✓ Vitamin D3 is found in animals / human beings 1) Lungs ➔ Vitamin D2 (ergocalciferol) differs from vitamin D3 High exposure to oxygen and air pollutants. only in the side-chain structure. Cells are particularly vulnerable to oxidative ➔ Both the cholecalciferol and the ergocalciferol damage. forms of vitamin D must undergo two further 2) Blood cells hydroxylation steps before the vitamin D Red and white blood cells passing through becomes fully functional. lungs. Exposed to oxidative stress during circulation. Calcidiol – liver 3) Other tissues Calcitriol – kidneys May protect tissues throughout the body from oxidative damage. ➔ Only a few foods, including liver, fatty fish (such as salmon), and egg yolks, are good natural ✓ Premature infants have low vitamin E stores. sources of vitamin D. ✓ Oxygen supplementation can increase ➔ Foods fortified with vitamin D include milk and oxidative stress. margarine. ✓ Vitamin E administration is crucial for antioxidant ➔ The rest of the body’s vitamin D supplies are protection. made within the body (skin) with the help of ✓ May contribute to overall health and reduce the sunlight. risk of chronic diseases associated with oxidative stress, such as heart disease and cancer. FUNCTIONS OF VITAMIN D 1) Maintains normal blood calcium and phosphate VITAMIN K levels. ➔ Like the other fat-soluble vitamins, vitamin K has 2) Stimulates absorption from the gastrointestinal more than one form. tract. ➔ The various forms differ structurally in the 3) Aids in retention by the kidneys. length and degree of unsaturation of the side 4) Triggers calcium salt deposition into bones. chain VITAMIN E Vitamin K1 ➔ The tocopherol form with the greatest biochemical ➔ Vitamin K1, also called phylloquinone, has a side activity is alpha-tocopherol chain that is predominantly saturated; only one ➔ Plant oils (margarine, salad dressings, and carbon–carbon double bond is present shortenings), green and leafy vegetables, and ➔ It is a substance found in plants. whole-grain products are sources of vitamin E. ➔ Vitamin E is easily destroyed by exposure to Vitamin K2 excessive heat and oxidation ➔ Vitamin K2 has several forms, called VITAMIN E AS AN ANTIOXIDANT menaquinones, with the various forms differing in the length of the side chain. ➔ Protects compounds from oxidation, acting as a ➔ Vitamin K2 is found in animals and humans and sacrificial molecule. can be synthesized by bacteria, including those ➔ Vitamin E is particularly important in found in the human intestinal tract. preventing the oxidation of polyunsaturated ➔ Menaquinones are the form of vitamin K found in fatty acids vitamin K supplements. Only leafy green ➔ It also protects vitamin A from oxidation vegetables such as spinach and cabbage are particularly rich in vitamin K. MTCC 117 CANLAS, F. C. 5  LESSON 3.2: VITAMINS ✓ Vitamin K is essential to the blood-clotting Thiamine Dry (neuromuscular) and wet (cardiac process (vitamin B1) failure) beriberi, Wernicke-Korsakoff syndrome ✓ Vitamin K is sometimes given to presurgical Pantothenic No syndrome recognized patients to ensure adequate prothrombin levels acid (vitamin B5) and to prevent hemorrhaging. Pyridoxine Cheilosis, glossitis, dermatitis, ✓ Vitamin K is also required for the biosynthesis of (vitamin B6) peripheral neuropathy, convulsions several other proteins found in the plasma, bone, Riboflavin Ariboflavinosis, cheilosis, angular and kidney. (vitamin B2) stomatitis, glossitis, dermatitis, corneal vascularization. VITAMIN FUNCTIONS Vitamin A Squamous metaplasia, especially Ascorbate (vitamin Many redox reactions, (retinol) glandular, follicular hyperkeratosis; C) hydroxylation of collagen xerophthalmia; night blindness, Biotin Cofactor in carboxylation reactions reproductive disorders, vulnerability to infection. Cobalamin (vitamin Folate metabolism and DNA B12) synthesis, maintenance of Vitamin D Rickets in children, osteomalacia in myelination of spinal tracts (cholecalciferol) adults, hypocalcemia, tetany Folate (folic acid) Transfer and use 1-carbon units in DNA and amino acid synthesis VITAMIN TOXICITY Niacin (nicotinic Incorporated into NAD and NAD Ascorbate (vitamin Cramps, diarrhea, nausea, kidney acid) phosphate, redox reactions C) stones. Thiamine (vitamin As pyrophosphate, is coenzyme in Scurvy B1) decarboxylation reactions Biotin No known toxicity. Pantothenic acid Incorporated in coenzyme A Cobalamin (vitamin No appreciable toxicity. (vitamin B5) B12) Pyridoxine (vitamin Derivatives are coenzymes in Folate (folic acid) Teratogenic effect in rodent model. B6) many intermediary reactions; No adverse effects at high oral amino acid, phospholipid and doses. glycogen metabolism Niacin (nicotinic Vascular dilatation, "flushing"; Riboflavin (vitamin Converted to flavin coenzymes, acid) hepatotoxic. B2) cofactor for many enzymes in Only when given parenterally. intermediary metabolism Thiamine (vitamin Headache, muscle weakness, Vitamin A (retinol) A component of retinal rod B1) cardiac arrhythmia, convulsions. pigment. Role in vision in dim light, Pantothenic acid Diarrhea. growth, reproduction. (vitamin B5) Maintenance of resistance to Pyridoxine (vitamin Atazia and sensory neuropathy. infection B6) Vitamin D Promotes absorption of calcium Riboflavin (vitamin Toxicity to riboflavin has not been (cholecalciferol) and phosphorus; mineralization of B2) reported. bones and teeth Absorption limited normally. Vitamin E Antioxidant, scavenges free Vitamin A (retinol) Acute: can cause drowsiness, (tocopherol) radicals, cellular respiration, headache, vomiting, stupor, skin primarily in muscle, RBC integrity peeling, and papilledema. Vitamin K Cofactor of procoagulants-hepatic Chronic: teratogenic, (phytomenadione) factors II (prothrombin), VII and X, osteoporosis, hepatotoxicity. protein C and protein S Carotenoids in excess, distinct orange-yellow skin color. VITAMIN DEFICIENCY SYNDROME Vitamin D Hypercalemia and its sequelae: Ascorbate Scurvy (cholecalciferol) hypercalciuria, bone (vitamin C) demineralization, constipation, muscle weakness, renal calculi. Biotin Rare. Caused by lack of biotin in total parenteral nutrition. Also, avidin in raw Vitamin E Mild Gl distress, nausea; egg whites binds biotin in gut, (tocopherol) coagulopathies in patients preventing absorption. Dermatitis, receiving anticonvulsants. glossitis, hair loss, anorexia, Vitamin K Foods containing vitamin K cause depression, and (phytomenadione) no toxicity problems. hypercholesterolemia. Excess amounts of vitamin K may Cobalamin Megaloblastic anemia, peripheral decrease clotting time. (vitamin B12) neuropathy Folate (folic Megaloblastic anemia, neural tube acid) defects REFERENCES Niacin (nicotinic Pellagra: dementia, dermatitis, acid) diarrhea Biochemistry (3rd ed.) by Stoker, H.S. Henry’s Clinical Diagnosis and Management by Laboratory Methods, 24th Edition by McPherson, R.A. & Pincus, M.R. MTCC 117 CANLAS, F. C. 6