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Questions and Answers
What is the primary role of transducin protein?
What is the primary role of transducin protein?
What deficiency sign is associated with vitamin A deficiency?
What deficiency sign is associated with vitamin A deficiency?
Which vitamin is essential for normal blood clotting?
Which vitamin is essential for normal blood clotting?
What can excessive intake of vitamin A lead to?
What can excessive intake of vitamin A lead to?
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Which form of vitamin K is primarily found in plants?
Which form of vitamin K is primarily found in plants?
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What is a potential effect of vitamin A toxicity during pregnancy?
What is a potential effect of vitamin A toxicity during pregnancy?
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Which of the following statements about vitamin K is incorrect?
Which of the following statements about vitamin K is incorrect?
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Which vitamin is crucial for the differentiation of epithelial tissues?
Which vitamin is crucial for the differentiation of epithelial tissues?
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Which group is primarily affected by insufficient exposure to daylight and deficiencies in vitamin D consumption?
Which group is primarily affected by insufficient exposure to daylight and deficiencies in vitamin D consumption?
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What is the primary source of vitamin A for the body?
What is the primary source of vitamin A for the body?
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How is dietary vitamin A absorbed in the intestinal cells?
How is dietary vitamin A absorbed in the intestinal cells?
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What is the role of the retinol-binding protein in vitamin A transport?
What is the role of the retinol-binding protein in vitamin A transport?
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What happens to retinol when it reaches the target cells of peripheral tissues?
What happens to retinol when it reaches the target cells of peripheral tissues?
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What is the mechanism by which retinoic acid regulates gene expression?
What is the mechanism by which retinoic acid regulates gene expression?
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What is the role of rhodopsin in the visual cycle?
What is the role of rhodopsin in the visual cycle?
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During vitamin A deficiency, which physiological function is most directly impaired?
During vitamin A deficiency, which physiological function is most directly impaired?
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Which of the following statements about vitamins is true?
Which of the following statements about vitamins is true?
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What distinguishes water soluble vitamins from fat soluble vitamins?
What distinguishes water soluble vitamins from fat soluble vitamins?
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What role does vitamin C play in the body?
What role does vitamin C play in the body?
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Which deficiency symptom is associated with a lack of ascorbic acid?
Which deficiency symptom is associated with a lack of ascorbic acid?
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What effect does vitamin C have on dietary nonheme iron absorption?
What effect does vitamin C have on dietary nonheme iron absorption?
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Which of the following is NOT a characteristic of fat soluble vitamins?
Which of the following is NOT a characteristic of fat soluble vitamins?
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What is a possible consequence of folic acid deficiency?
What is a possible consequence of folic acid deficiency?
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How quickly can deficiencies in water soluble vitamins manifest?
How quickly can deficiencies in water soluble vitamins manifest?
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Study Notes
Vitamins
- Vitamins are organic compounds needed by humans in small amounts
- They are not produced in adequate quantities by the body and must be obtained from the diet.
- Vitamins are classified as water-soluble or fat-soluble.
Water-Soluble Vitamins
- Water-soluble vitamins are easily excreted in urine and do not typically accumulate in the body.
- Deficiencies can develop quickly.
- Examples include folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid.
Fat-Soluble Vitamins
- Fat-soluble vitamins are absorbed, transported, and stored with dietary fat.
- They are not readily excreted, so significant amounts can accumulate in the liver and adipose tissue.
- Deficiencies can take years to develop.
- Examples include vitamins A, D, K, and E.
Vitamin C
- Ascorbic acid, the active form, is a crucial reducing agent in the body.
- It's a coenzyme in hydroxylation reactions, required for connective tissue (collagen) synthesis and wound healing.
- Vitamin C facilitates the absorption of non-heme iron in the digestive tract.
- Deficiency results in scurvy, a condition characterized by sore gums, loose teeth, fragile blood vessels, hemorrhage, swollen joints, and fatigue, defective connective tissue, and microcytic anemia.
Folic Acid
- Tetrahydrofolate (THF) is the reduced coenzyme form crucial for one-carbon metabolism.
- It receives one-carbon fragments from various donors, transferring them to intermediates in the synthesis of amino acids, purine nucleotides, and the pyrimidine nucleotide thymidylate.
- A deficiency can result in megaloblastic anemia due to diminished synthesis of purine nucleotides and TMP.
- This will also impair cell division.
- Common causes include increased demand (pregnancy/lactation), malabsorption, alcoholism, and drugs like methotrexate.
Vitamin B12
- Vitamin B12 is synthesized exclusively by microorganisms and is not present in plants.
- It acts as a coenzyme in two essential reactions:
- re-methylation of homocysteine (Hcy) to methionine.
- isomerization of methylmalonyl coenzyme A (MMA) to succinyl CoA.
- B12 deficiencies result in unusual branched-fatty acids accumulating in cell membranes, especially in the nervous system.
- It's crucial for the proper functioning of the central nervous system.
- Vitamin B12 is absorbed in the stomach and intestines, requiring intrinsic factor.
- Deficiency can be caused by insufficient intake, malabsorption issues such as pernicious anemia (lack of intrinsic factor) or gastrectomy, and increased demand (pregnancy/lactation).
Folate Trap in Vitamin B12 Deficiency
- Folate cannot be converted to other THF forms, the N5-methyl form accumulates,
- The levels of other THF forms decrease, resulting in a deficient supply of the required THF forms for cellular function.
Vitamin B12 Deficiency
- In contrast to other water-soluble vitamins, vitamin B12 stores are significant and can last for years, resulting in a delayed onset of deficiency symptoms
- May be caused by reduced intake, increased demands (pregnancy/lactation); or malabsorption problems (pernicious anemia).
- Symptoms can be lifelong if untreated, and often include neurological manifestations.
Absorption of Vitamin B12
- B12 is released in the stomach from food.
- It binds to R-protein/haptocorrin.
- The complex moves through the intestine.
- Pancreatic enzymes release B12 from R-protein.
- B12 binds to intrinsic factor (IF).
- The cobalamin-intrinsic factor complex (B12-IF complex) is formed.
- The complex travels through the intestines and binds to a receptor.
- Cobalamin (B12 in the complex) enters the mucosal cell then the circulatory system and is stored in the liver.
- B12 is released into bile and efficiently reabsorbed.
Pernicious Anemia
- An autoimmune condition where the stomach's parietal cells are destroyed (lack of IF).
- B12 cannot be absorbed.
- Patients with prior gastric surgery (or gastrectomy) are at risk.
- Deficiency can cause various neurological and psychological symptoms.
Pyridoxine (Vitamin B6)
- Includes pyridoxine, pyridoxal, and pyridoxamine.
- All have a pyridine ring, but differ in the functional group.
- Exists as pyridoxal phosphate (PLP), the biologically active coenzyme.
- PLP is a coenzyme for many enzymes involved in amino acid metabolism.
- Deficiency is rare but can be observed in malnourished infants, women on oral contraceptives; and those with alcoholism.
- Toxicity observed at higher doses (over dietary recommendations).
Thiamine (Vitamin B1)
- Exists as thiamine pyrophosphate (TPP), the active form of the molecule.
- TPP is crucial in carbohydrate metabolism, oxidative decarboxylation of pyruvates and a-ketoglutarate;
- Essential for proper function of the central nervous system.
- Deficiency results in symptoms such as beriberi and Wernicke-Korsakoff syndrome (typically associated with chronic alcohol abuse).
Niacin (Vitamin B3)
- Exists as nicotinamide adenine dinucleotide (NAD+), and its phosphorylated derivative, nicotinamide adenine dinucleotide phosphate (NADP+).
- These are important coenzymes in oxidation-reduction reactions.
- Can be synthesized from the amino acid tryptophan.
- Deficiency leads to pellagra (with symptoms of dermatitis, diarrhea, and dementia),
- Toxicity arises at high dosage.
Riboflavin (Vitamin B2)
- Active forms include flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
- FMN and FAD are crucial for oxidation-reduction reactions.
- deficiency does not result in major diseases typically.
Biotin (Vitamin B7)
- A carrier of activated carbon dioxide in various carboxylation reactions, such as the synthesis of fatty acids and amino acids.
- Biotinidase is enzyme necessary for recycling of biotin, and deficiency is a notable cause of newborn screening tests.
- Dietary biotin deficiency can be induced through dietary restrictions.
Pantothenic Acid (Vitamin B5)
- A component of coenzyme A (CoA) essential in acyl group transfer.
- Also involved in fatty acid synthesis pathways.
- Deficiencies don't appear to be common.
Vitamin D
- Vitamin D is a group of sterols with hormone-like functions.
- The active form is 1,25-dihydroxycholecalciferol (calcitriol).
- Calcitriol regulates calcium and phosphorus levels through effects on the intestines, kidneys, and bone.
- Vitamin D is synthesized in the skin via UV light exposure.
Vitamin K
- Functions in post-translational modification of proteins, notably in blood clotting (glutamic acid residues).
- Vitamin K, exists in plant (phylloquinone (K1)) and microbial (menaquinone (K2)) form. - Deficiency in infants is common due to their sterile gut; bacterial production is missing, and this is remedied by injection.
- Warfarin, an anticoagulant, inhibits Vitamin K epoxide reductase.
Vitamin E
- A group of tocopherols with antioxidant activity, primarily a-tocopherol.
- Protects against non-enzymatic oxidation.
- regeneration of vitamin E active form is important.
Vitamin A
- Retinol is the preformed vitamin.
- also exists as retinoids- retinoids include naturally occurring forms of Vitamin A (retinol and metabolites) and synthetic forms (drugs
- retinoids function in vision, reproduction, tissue growth and maintainence of epithelial tissue.
- deficiency may cause night blindness.
- Toxic effects at high dosage (e.g., liver enlargement).
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Test your knowledge on essential vitamins, their functions, and the health implications of deficiencies and toxicities. This quiz covers Vitamin A and K, along with their roles in the body, dietary sources, and mechanisms of action. Perfect for nutrition students and health enthusiasts!
