Folic Acid and THF Functions

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Questions and Answers

What is the maximum amount of Vitamin B12 that is needed per day?

10 mg

10 μg

50kDa

0.0002 mg (correct)

What is the role of Intrinsic Factor (IF) in Vitamin B12 absorption?

IF competes with other nutrients for absorption in the ileum.

IF directly transports Vitamin B12 into the bloodstream.

IF binds to Vitamin B12 and facilitates its absorption in the ileum. (correct)

IF breaks down Vitamin B12 into smaller, absorbable molecules.

What is the primary source of Vitamin B12 in the diet?

Plant-based foods such as legumes and leafy greens.

Dietary supplements.

Fortified foods such as cereals and bread.

Animal products such as meat, poultry, and dairy. (correct)

What is the mechanism of action (MOA) of Vitamin B12 deficiency in terms of folate metabolism?

Vitamin B12 deficiency prevents the conversion of folate into its active form. (A) Signup and view all the answers

What is the relationship between Vitamin B12 and homocysteine?

Vitamin B12 deficiency leads to an increase in homocysteine levels. (C) Signup and view all the answers

Which of the following statements about the function of Vitamin D is NOT true?

Vitamin D directly stimulates osteoclasts, leading to increased bone resorption. (D) Signup and view all the answers

What is the primary function of osteoclasts in the skeletal system?

To break down bone tissue. (B) Signup and view all the answers

Which of the following is a consequence of prolonged vitamin D deficiency?

Development of rickets or osteomalacia. (B) Signup and view all the answers

Why is adequate exposure to sunlight essential for maintaining bone health?

Sunlight allows for the synthesis of vitamin D, which is crucial for calcium absorption. (D) Signup and view all the answers

Which of the following statements about Vitamin E is TRUE?

Vitamin E can only be acquired through dietary intake. (D) Signup and view all the answers

Which of the following conditions can be caused by a deficiency in magnesium?

Osteoporosis (B) Signup and view all the answers

What is the most common nutritional deficiency disease?

Iron deficiency (D) Signup and view all the answers

What is the primary function of iron in the body?

Oxygen transport (B) Signup and view all the answers

Which of the following is NOT a symptom of zinc deficiency?

Increased appetite (D) Signup and view all the answers

Which of the following is a consequence of hypercalcemia?

Diffuse precipitation of calcium phosphate (C) Signup and view all the answers

What is the primary function of calcium in the body?

All of the above (D) Signup and view all the answers

In which of the following groups is iron deficiency most common?

All of the above (D) Signup and view all the answers

What is the main reason for the high requirement of iron in pregnant teenagers?

Continuing growth of the teenager and the fetus (C) Signup and view all the answers

What is the primary function of SAM (S-adenosyl methionine) in the context of the provided text?

SAM is a methyl group donor involved in methylation reactions. (C) Signup and view all the answers

What is the direct consequence of a lack of Vitamin B12 in the context of the text?

A deficiency in Vitamin B12 leads to the accumulation of Methyl-THF, preventing the regeneration of THF. (D) Signup and view all the answers

Which of the following is a consequence of a deficiency in Vitamin C?

Impaired synthesis of collagen, leading to weak connective tissue and the development of scurvy. (B) Signup and view all the answers

What is the primary role of carnitine in the body, as mentioned in the text?

Carnitine serves as a carrier for the transport of fatty acids into the mitochondrial matrix for energy production. (A) Signup and view all the answers

What is the primary role of bile salts in the body, as described in the text?

Bile salts emulsify fat droplets, increasing their surface area for efficient digestion by enzymes. (A) Signup and view all the answers

What is the primary difference between the role of Vitamin B12 and Vitamin C as described in the text?

Vitamin B12 is essential for the regeneration of THF, while Vitamin C is involved in various hydroxylation reactions. (B) Signup and view all the answers

What is the primary function of Vitamin C as an antioxidant, according to the provided information?

Vitamin C directly removes free radicals by donating electrons to them, preventing damage to cells. (D) Signup and view all the answers

What is the significance of the hydroxylation reaction in the context of collagen synthesis as mentioned in the text?

Hydroxylation of prolyl and lysyl residues in procollagen is essential for the formation of strong and stable collagen fibers. (A) Signup and view all the answers

What is the primary role of norepinephrine in the body, as described in the text?

Norepinephrine is a "stress hormone" that mobilizes energy by increasing blood sugar levels. (D) Signup and view all the answers

In the context of the provided text, what is the primary reason why a deficiency in Vitamin C can lead to fatigue and lassitude?

Vitamin C deficiency disrupts the synthesis of carnitine, leading to decreased ATP production and reduced energy availability. (D) Signup and view all the answers

What is the effect of a THF deficiency on DNA synthesis?

Inhibition of DNA synthesis (C) Signup and view all the answers

Which of the following is a key source of folate?

Uncooked fruits (D) Signup and view all the answers

How does methotrexate affect folate metabolism?

Methotrexate inhibits the formation of THF (D) Signup and view all the answers

What characteristic distinguishes megaloblastic anemia from other types of anemia?

Presence of abnormally large red blood cells (C) Signup and view all the answers

What is the relationship between folate deficiency and megaloblastic changes in red blood cells?

Folate deficiency leads to impaired nuclear maturation in red blood cells (A) Signup and view all the answers

Which of the following is NOT a characteristic of megaloblastic anemia?

Increased red blood cell count (A) Signup and view all the answers

What is the primary function of vitamin C in the context of the provided information?

It converts dehydroascorbate back to ascorbate, replenishing its antioxidant capacity. (D) Signup and view all the answers

What is the main reason why fat-soluble vitamins should be taken with a fatty meal?

Fatty meals stimulate the secretion of bile salts, which help in the absorption of fat-soluble vitamins. (C) Signup and view all the answers

Which of the following is NOT a form of vitamin A listed in the text?

Retinoid (A) Signup and view all the answers

What is the primary role of retinol phosphate in the context of vitamin A function?

It is involved in the transfer of carbohydrates onto proteins, crucial for glycoprotein synthesis. (C) Signup and view all the answers

Which of the following is a direct consequence of a vitamin A deficiency, as described in the text?

A decrease in the glycoprotein content of tears, leading to dry eyes. (A) Signup and view all the answers

How does vitamin A contribute to the maintenance of epithelial tissues?

It promotes the synthesis of glycoproteins, which are important components of epithelial cell membranes and secretions. (A) Signup and view all the answers

What is the primary function of β-carotene in the context of vitamin A?

It is a precursor to retinal, the aldehyde form of vitamin A found in rhodopsin. (C) Signup and view all the answers

Which TWO options accurately describe the characteristics of micelles?

Micelles are composed of bile salts and encapsulate water-insoluble molecules. (C), Micelles are large structures, typically 100-200nm in diameter. (D) Signup and view all the answers

Study Notes

Folic Acid

Latin name: "folium" = leaf
Best sources: Green leafy vegetables, uncooked fruits
In intestinal mucosa: Folate reductase converts to dihydrofolate reductase, then to THF (tetrahydrofolate) using 2 NADPH2 to 2 NADP
Anticancer drug Methotrexate prevents THF formation

Function of THF

Carrier of one-carbon units
Used in biosynthetic reactions
Required for purine and thymidine nucleotide synthesis (DNA building blocks)
Lack of THF results in lack of DNA reduplication and mitosis

THF Deficiency

Clinical expression: Megaloblastic changes (large cytoplasm)
Reason: DNA synthesis is inhibited; DNA replication and nuclear maturation are impaired; cytoplasmic maturation is unaffected
Hematological Changes: Megaloblastic anemia (macrocytic anemia)
Large, but not enough erythrocytes
Folic acid requirements increase during pregnancy
THF deficiency during pregnancy can lead to birth defects

Vitamin B12 (Cobalamin)

Source: Synthesized only by microorganisms (no cobalamin in plants)
Animal products are the only dietary source
Strict vegetarians are at risk for deficiency
Liver stores up to 10 mg
Only 0.0002 mg needed daily
Stored amount lasts 136 years; if intestinal absorption is normal
Clinical symptoms within 2 years if intestinal absorption is impaired

Vitamin B12 Absorption

B12 alone is not absorbed
Daily intake up to 10 ug B12 via bile from liver to duodenum and ileum, then excretion
Dietary B12 travels from stomach towards excretion
Parietal cells secrete intrinsic factor (50kDa glycoprotein)
Intrinsic factor creates a tight complex with B12, which is absorbed in the ileum
In blood, it is replaced by transcobalamin (transport protein)
Transcobalamin prevents renal excretion & mediates uptake of B12 into tissues

Vitamin B12 Deficiency

Megaloblastic anemia, indistinguishable from THF deficiency
MOA: "Methyl folate trap"

Vitamin C (Ascorbic Acid)

Structure identified in 1932, isolated from lemon juice
MOA: Oxidation of vitamin C (-2H+ - 2e-)
Large doses plus large amounts of calcium in daily diet can lead to kidney stones
- Degradation: hydrolysis of inner ester(lactone) to dehydroascorbic acid and further degradation to oxalate.
Physiological function: Hydroxylation
- One oxygen atom is inserted between carbon and hydrogen to form a hydroxyl group
- 2nd oxygen reacts with 2H from Vit C to produce water
- Several physiological hydroxylation reactions affected by Vit C deficiency
Physiological Vitamin C dependent hydroxylation reactions: -Hydroxylation of prolyl and lysyl residues in procollagen (essential for collagen synthesis; deficiency leads to scurvy) -Synthesis of carnitine (carrier for transport of fatty acids into mitochondrial matrix; deficiency leads to decrease in ATP energy level)

Vitamin D

Minimal exposure to sunlight leads to sufficient endogenous synthesis
MOA: Induces synthesis of Ca-binding proteins, interacting with DNA (regulation of transcription) via 7-Dehydrocholesterol (Cholesterol) and conversion of Cholecalciferol (Vitamin D3) to 1,25-Dihydroxycholecalciferol (Calcitriol)
Physiological Functions: -Release of Ca from bone
- Intestinal calcium absorption
- Prevent renal calcium excretion
Long-term deficiency:
- Ca in blood stays constant, but bone tissue is depleted of calcium
- Bone tissue poorly mineralized resulting in softening
- Rickets (children), osteomalacia (adults)
Hypervitaminosis D:
- Chronic elevation of blood calcium levels leads to cardiovascular and renal damage

Vitamin E (Tocopherol)

More than 8 derivatives in plants, differing in ring substitutions and side chains
α-Tocopherol is most abundant
Deficiency is rare; mild hemolytic anemia in premature infants due to poor intestinal absorption
Non-toxic at 50x RDA
Epidemiological studies suggest inverse relationship between Vitamin E intake and coronary heart disease

Vitamin K

Coagulation
Phylloquinone (in vegetables)
Menaquinone (synthesized by bacteria)
Menadione (synthetic previtamine); alkylated in the human body
Absorbed easily, even without bile salts
Not significantly stored. First fat-soluble vitamin to be deficient in fat malabsorption.
Deficiency results in bleeding disorders
Hemorrhagic diseases of newborns happen due to low tissue stores at birth, insufficient Vitamin K in breast milk, and immature intestinal flora/inadequate bacterial production
Essential co-enzyme for the carboxylation of glutamate residues in prothrombin

Micronutrients (Minerals)

Minerals comprise about 4-5% of total body weight
50% = calcium (Ca); 25% = phosphorus (P) in bones and teeth
Remaining 25% is other essential macro/micro minerals & trace elements.
Essential Macrominerals ( >100 mg/day): Mg, Na, K, Cl, S, etc.
Essential Microminerals (<15 mg/day): Fe, Zn, I, Se, Mn, F, Mo, Cr, Co, B, etc.
Ultratrace Elements (micrograms): As, Al, Sn, Ni, V, Si, etc
"Problem Minerals" (in the U.S. diet): Low intake of calcium, iron, zinc, and magnesium. Food fortification with iron and zinc is common, but not calcium.
Calcium and Phosphate: 99% of total body calcium in bones, and 2.5 mM in blood (tightly regulated). Intracellular Ca: 100-1000 nM, but essential for majority of physiologic processes.
- Hypocalcemia: low blood calcium, causes muscle spasms, tetany, cardiac dysfunction.
- Hypercalcemia: high blood calcium, causes diffuse precipitation of (Ca)3(PO4)2
Magnesium (Mg): Key component for >300 metabolic enzymes and is essential component of ATP. No cAMP formation without Mg

Vitamin A

Source #1: Beta-carotene = orange pigment, carrots, and other vegetables
Beta-carotene dioxygenase in intestinal mucosa oxidizes carotene to 2 molecules of retinal
Retinal is a prosthetic group in rhodopsins
Deficiency: Night blindness
Other Forms:
- Retinol (alcoholic group) = storage form in animal tissues
- Retinal (aldehyde group) = in rhodopsin
- Retinoic acid (carboxylic group) = involved in gene expression.
- Retinophosphoate (ester of retinol and phosporic acid) = crucial for carbohydrate transfer reactions onto proteins; important for synthesis of glycoproteins
Deficiencies:
- Maintenance of epithelial tissues via synthesis of glycoproteins; deficiency leads to slowed down mucus producing cells and low glycoprotein content of tears, "dry eyes" (xerophthalmia), bacterial infections, and corneal perforation
- Function of osteoblasts and osteoclasts; deficiency leads to impaired balance between these, and retinoic acid activates osteoclasts, enhancing bone resorption.

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Description

This quiz covers the essential aspects of folic acid, including its sources, functions, and the implications of THF deficiency. Participants will explore the significance of THF in DNA synthesis and the potential health consequences of its deficiency, particularly during pregnancy. Test your knowledge on how folic acid plays a crucial role in human health.