Nutrition and Vitamins Quiz

Introduction to Vitamins and Coenzymes

• Vitamins are nutritionally important organic compounds
• Vitamins are required in very small amounts
• Vitamins cannot be synthesized by the human body
• Vitamins do not undergo degradation for energy production unlike carbohydrates and lipids
• Some mammals can synthesize vitamin C; humans and primates cannot
• No mammal can synthesize B vitamins, but rumen bacteria can
• Some compounds function as vitamins after chemical modifications (provitamins)

Origin of the Term "Vitamin"

• Casimir Funk, a Polish biochemist, isolated an anti-beriberi substance from rice polishing
• He named it "vitamine" (vital for life)
• Initially, it was believed that these essential compounds were all amines, hence "vital amines"
• Later, it was discovered some compounds weren't amines, and the name was changed to vitamins

Coenzymes, Cofactors, and Prosthetic Groups

• Cofactors are nonprotein components of enzymes
• Cofactors can be metal ions or organic molecules (vitamins)
• Cofactors bind to enzymes either loosely or tightly
• Tightly bound cofactors are considered prosthetic groups

Holoenzyme=Active enzyme

• Holoenzyme (active form) consists of apoenzyme (in-active form) and cofactors

Vitamin Classification

• Lipid-soluble vitamins (A, D, K, E) are more soluble in fats, hydrocarbons, and similar solvents than water
• Water-soluble vitamins (C, B complex) are more soluble in water than organic solvents

Water Soluble Vitamins

• Absorption is easy via circulation without carriers
• Not stored in the body
• Excreted via urine
• Not toxic in case of overconsumption
• Examples: B vitamins and Vitamin C

Vitamin B Complex - General Features

• Act as components of coenzymes in metabolism of carbohydrates, lipids and proteins
• Dietary requirements are closely linked to metabolic rate
• Absorbed by passive diffusion in small intestine, except B12
• Excess is excreted in urine; little or no tissue storage, except B12 and some folic acid
• Must be supplied in diet (or through ruminal synthesis)

Vitamin B1 - Thiamine

• Found in yeast, whole grains, legumes, enriched grain products, and meat
• Functions in producing energy from carbohydrates, proper nerve function, appetite stability, promoting growth and good muscle tone, ATP production

Metabolic Pathways Requiring Thiamin Pyrophosphate (TPP)

• TPP is an essential coenzyme for oxidative decarboxylation
• It is required for nerve function (unrelated to coenzyme activity)
• Examples of metabolic pathways include glycolysis, TCA cycle, branched chain amino acids, and branched chain acyl-CoA

Thiamine Deficiency (B1) Beriberi

• Dry beriberi: peripheral neuropathy, decreased muscle strength, and muscle paralysis
• Wet beriberi: cardiomegaly, tachycardia, and edema

Alcohol, Wernicke-Korsakoff Syndrome

• In extreme cases, beriberi is associated with Wernicke-Korsakoff syndrome
• Wernicke encephalopathy and Korsakoff syndrome are forms of brain damage caused by thiamine deficiency
• Ataxia, confusion, memory loss, ophthalmoplegia, and nystagmus are symptoms

Vitamin B2 or Riboflavin

• Needed for good vision and healthy skin
• Made of the sugar alcohol ribitol and flavin

Riboflavin Functions

• Essential constituent of flavoproteins (FMN and FAD)
• Functions involve hydrogen carriers in glycolysis, TCA cycle, fatty acid and amino acid oxidation, mitochondrial respiratory chain, and oxidative phosphorylation

Riboflavin Deficiency Symptoms

• Cheilosis/angular stomatitis, glossitis, localized seborrheic dermatitis on the face

Niacin or Vitamin B3

• Synthesized in the body from the essential amino acid tryptophan
• Nicotinic acid and nicotinamide have biological activity
• As the nicotinamide ring of the coenzymes NAD and NADP

Niacin Functions

• Active coenzymes: Nicotinamide-adenine dinucleotide (NAD+) and Nicotinamide-adenine dinucleotide phosphate (NADP+)
• Important in hydrogen transfer reactions catalyzed by dehydrogenases
• Involved in ATP synthesis from oxidation of primary fuels (glucose, fatty acids, and amino acids) (NAD+)
• Important in reductive biosynthesis (NADP+)

Niacin Deficiency (Pellagra)

• Occurs in people who subsist mainly on corn, which is low in niacin and tryptophan
• Symptoms of pellagra include dermatitis, diarrhea, and dementia

Vitamin B5 or Pantothenic Acid

• Part of coenzyme A (CoA) and acyl carrier proteins (ACPs)
• Involved in metabolic reactions including the citric acid cycle, fatty acid oxidation, oxidative decarboxylation of pyruvate, synthesis of cholesterol, bile salts, ketones, and steroid hormones
• Prosthetic group in fatty acid synthesis
• Deficiency is rare in humans

Vitamin B6

• Functions: amino acid metabolism, transamination, decarboxylation reactions, glycogen breakdown, synthesis of epinephrine/norepinephrine, synthesis of niacin (vitamin B3), transamination reactions, deamination, decarboxylation, condensation (reactions)

Vitamin B6 Deficiency

• Deficiencies are rare and usually related to an overall deficiency of all the B-complex vitamins
• Causes abnormalities of tryptophan and methionine metabolism, increased steroid hormone activity, and development of hormone-dependent cancers
• Penicillamine and Isoniazid form complexes with PL & PLP, causing sensory neuropathy
• Status is measured by activation of erythrocyte transaminases by pyridoxal phosphate added in vitro, as well as plasma concentrations of vitamin B6

Biotin

• Sources: liver, soybeans, egg yolk, cereals, legumes, nuts; occurs combined with lysine (biocytin) or other proteins
• Intestinal bacteria can synthesize biotin
• Functions to transfer CO2 in a small number of reactions, including acetyl-CoA carboxylase and crucial steps in de novo fatty acid synthesis

Biotin Deficiency

• Deficiency is unknown, except in people on total parenteral nutrition or those who eat uncooked egg whites
• Symptoms include lethargy, depression, hallucinations, anorexia, nausea, and loss of hair, dermatitis

Folic Acid (Folate)

• Obtained from yeasts, leafy vegetables, and animal liver; raw foods have more than cooked foods

Folic Acid (Folate) Functions

• Active form: tetrahydrofolate (THF)

Folic Acid (Folate) Metabolism

• Involved in reactions such as dUMP to dTMP in DNA synthesis, THF conversion/maintenance for folate metabolism, and serine/glycine hydroxmethyl transferase
• Methyl group transfer reactions are key

Folate Deficiency Symptoms

• Deficiency may occur due to poor dietary habits (alcoholics), impairment of absorption due to anticonvulsants or oral contraceptives, or in pregnancy
• Symptoms result in impairment of TMP and purine synthesis; cell cycle arrest; megaloblastic anemia; neural tube defects (NTD) like spina bifida; and cardiovascular disease

Vitamin B12 (Cobalamin)

• Cobalt-containing compound with a corrin ring
• Forms: cyanocobalamin, hydroxycobalamin; adenosylcobalamin, and methylcobalamin
• Synthesized by microorganisms (bacteria) and found in muscle meats, fish, shellfish, dairy products, and eggs

Vitamin B12 Metabolic Pathways

• Essential for the catabolism of fatty acids (odd-number carbon atoms), amino acids (valine, isoleucine, and threonine), and cholesterol

Vitamin B12 Absorption

• Ingested vitamin B12 is absorbed via the dissociation of the R-Cbl complex (R-protein) in low pH.
• Intrinsic factor (IF) from gastric parietal cells binds to B12
• The B12-IF complex enters the ileum
• Then absorbed, and transported via transcobalamin II to other tissues; stored in the liver attached to transcobalamin I

Vitamin B12 Deficiency

• Pernicious anemia: failure of vitamin B12 absorption due to intrinsic factor secretion failure or autoimmune disease
• Neurological disorders: progressive demyelination of nerve cells due to methylmalonyl-CoA increase

Vitamin C (Ascorbic Acid)

• Derived from glucose via the uronic acid pathway
• L-gluconolactone oxidase converts gluconolactone into ascorbic acid
• Ascorbic acid and dehydroascorbic acid have vitamin activity

Vitamin C Functions

• Anti-oxidative agent; collagen synthesis (proline and lysine hydroxylases); copper-containing hydroxylaes; enhancing iron absorption; carnitine synthesis; role in proline hydroxylase in osteocalcin formation; blood clotting cascade; scar tissue repair

Vitamin C Deficiency (Scurvy)

• Fragility of blood capillaries
• Bleeding gums, tooth loss
• Small red spots on skin
• Rough skin
• Wounds fail to heal
• Weak bones
• Anemia and infections

Fat Soluble Vitamins

• Include vitamins A, D, E, and K
• Require appropriate digestion for absorption, often via lipoproteins
• Stored in adipose and liver tissue, excreted via bile
• Risk of toxicity with high supplement intake

Vitamin A

• Retinoids contain a beta-ionone ring and an isoprenoid side chain with hydroxyl, aldehyde, or carboxylic acid groups
• Provitamin A: alpha, beta, and gamma-carotenes
• Essential for vision (rhodopsin), growth, development, tissue differentiation, immune system function, antioxidant protection

Vitamin A Uptake, Absorption, Transport & Storage

• Retinyl esters are absorbed
• Beta-carotene is converted into retinol
• Retinol is transported to the liver

Vitamin A Deficiency

• The most important preventable cause of blindness because of disruption in the cornea
• Symptoms include night blindness, xerophthalmia, immunity impairments , and anemia

Vitamin A: Toxicity

• Occurs with high intake, often through consumption of polar bear liver
• Symptoms include central nervous system problems (headache, nausea,taxia)
• Liver problems (hepatomegaly with histological changes, hyperlipidemia)
• Calcium homeostasis issues (bone thickening, hypercalcemia, soft tissue calcification)
• Skin problems (excessive dryness, alopecia)

Vitamin D

• Not strictly a vitamin; synthesized in skin with adequate UV light
• Important forms: Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol)
• Functions: regulation of calcium absorption and homeostasis
• Most actions are mediated by nuclear receptors

Vitamin D Synthesis in the Skin

• 7-Dehydrocholesterol is converted to previtamin D; further converted to cholecalciferol (Vitamin D) with UV light

Vitamin D Synthesis and Activation

• Cholecalciferol converted to calcidiol (25-hydroxyvitamin D3) by the liver
• Calcidiol further converted to calcitriol (1,25-dihydroxyvitamin D3) by the kidneys
• Essential for normal insulin secretion

Vitamin D Deficiency

• Rickets in children: undermineralized bones due to poor calcium absorption
• Osteomalacia in adults: demineralization of bone, especially in women with limited sunlight exposure

Higher Intake of Vitamin D

• Protective against prostate and colorectal cancer, prediabetes, and metabolic syndrome
• High intake is toxic: nausea, loss of appetite, hypercalcemia, calcium deposition in soft tissues, arteries, and kidneys

Vitamin E

• Generic descriptor for tocopherols and tocotrienols
• Acts as a lipid-soluble antioxidant in cell membranes
• D-alpha tocopherol protects LDLs from oxidation; moderates cholesterol lowering capabilities, helps maintain cell membrane fluidity
• Inhibits blood platelet "clumping" preventing clots

Vitamin E Deficiency

• Rare in humans
• Severe fat malabsorption, cystic fibrosis, chronic liver disease are possible causes
• Symptoms include nerve and muscle membrane damage; premature infants may have inadequate reserves; erythrocyte membranes are abnormally fragile due to lipid peroxidation
• May lead to hemolytic anemia

Vitamin K

• "K" from "koagulation" (blood clotting)
• Three forms: phylloquinone (K1), menaquinones (K2), and menadione (K3)
• Phylloquinone is the normal dietary source (green vegetables)
• Menaquinones are synthesized by intestinal bacteria—varying lengths of side chains
• Menadione is a synthetic water-soluble vitamin
• Antagonists (e.g., warfarin) reduce blood clotting in thrombosis risk

Vitamin K Functions (gamma-Carboxylation)

• Carboxylation of specific glutamate residues in calcium-binding proteins;
• Prothrombin and other blood clotting proteins, osteocalcin and matrix Gla protein are examples
• Nephrocalcin in the kidney

Vitamin K Deficiency

• Prolonged antibiotic use
• Malabsorption or biliary tract obstruction
• Patients, especially immediate post-natal infants, may have insufficient stores or low intake (low breast milk vitamin K)
• Causes elevated prothrombin times (PT) and bleeding time (BT)

Fat Soluble vs. Water Soluble Vitamins

• Summary table of differences in absorption, transport, storage, excretion, toxicity, and requirements of soluble and fat-soluble vitamins

Test your knowledge on the functions and deficiency symptoms of essential vitamins. This quiz covers vitamin D, A, and riboflavin, including their roles in the body and associated health conditions. Challenge yourself to see how well you understand these critical nutrients!