folic acid and vit B12

Question 1

def the vitamins

Answer 1

-vitamins are organic compounds occurring in small quantities in different natural foods.
- essential factors that must be supplied in diet . they aren’t synthesized by humans .
- they can’t be used as fuel “ not oxidized to produce energy “ & not enter in the structure of tissues
- serve as coenzymes required for metabolism of carbohydrate , lipid and protein

Question 2

list causes of vitamin deficiency

Answer 2

1. inadequate dietary intake or malabsorption : e.g. biliary obstruction , pancreatitis
2. dysfunction or absence of proteins required to absorption , transport , activation or utilization
3. inc excretion as in kidney disease
4. drug related :
   - antibiotic therapy kills intestinal microorganisms cause vit K deficiency
   - anti TB drug isoniazid can dec vit B6 absorption

Question 3

classify vit B family

Answer 3

1. energy related :
   - thiamine (B1)
   - biotin (B7)
   - riboflavin (B2)
   - niacin (B3)
   - pantothenic acid (B5)
2. hematopoietic :
   - folic acid (B9)
   - vit B12
3. others :
   pyridoxine (B6)

Question 4

list chc of fat soluble vitamins

Answer 4

1. fat soluble
2. water insoluble
3. require the presence of lipid and bile salts for absorption
4. require carrier protein
5. stored in liver
6. not excreted
7. occur deficiency only when stores are depleted
8. occur toxicity
9. ttt of deficiency = single large dose
10. example = vit A D E K

Question 5

list chc of water soluble vitamins

Answer 5

1. fat insoluble
2. water soluble
3. simple absorption
4. not require carrier protein
5. not storage
6. excreted in urine
7. deficiency occur rapidly as there is no storage
8. toxicity = unlikely
9. ttt of deficiency= regular dietary supply
10. example = vit C & B complex

Question 6

illustrate the chemistry of vit B9 ( folic acid) and sources

Answer 6

1.chemistry :
pteridine ring + poly glutamic AA 2-7 + PABA “ para amino benzoic acid “
2.sources :
-best source is liver & green leafy vegetables
-can’t be synthesized by human or animal
-can be synthesized by intestinal bacteria –active form = THF “ tetrahydrofolate”

Question 7

list daily requirement of vit B9 in :
normal & pregnancy condition

Answer 7

• 400 microgram / day
• 800 microgram / day in pregnancy and lactation

Question 8

list function of vit B9

Answer 8

1. carrier of one Carbon unite “ except CO2”
2. synthesis of DNA “ replication “ :
   purine & thymine
3. synthesis of serine & glycine
4. synthesis of methionine & choline , methyl (CH3) synthesize methionine from homocysteine “ need vit B12 “

Question 9

list causes of folate deficiency

Answer 9

1. inc rate of cell division e.g. pregnancy , anemia
2. poor absorption
3. administration of methotrexate as anticancer
4. vit B12 deficiency “ folate trap “

Question 10

what’s the effect of folate deficiency ?

Answer 10

defect cell proliferation due to defect in DNA synthesis
“ megaloblastic anemia , immature RBCs in BM & blood “

Question 11

what’s the effect of PABA analogs ( sulfa drug ) on vit B9 as antagonist?

Answer 11

-prevent folic acid synthesis by bacteria ( antibiotic )
-inhibit dihydropteroate synthetase

Question 12

what’s the mechanism of folic acid analogs (methotrexate ) as antagonist ?

Answer 12

competitive inhibit dihydrofolate reductase (used as anticancer)

Question 13

what’s trimethoprim ?

Answer 13

-folic acid antagonist , act on bacteria only
- inhibit folate reductase & used as antibiotic

Question 14

illustrate chemistry of vit B12(cobalamin)

Answer 14

• corring ring system that differs from porphyrins in that two of the pyrrol rings are linked directly rather than through a methenyl bridge
• cobalt ( give red color )

Question 15

illustrate the sources of vit B12 (cobalamin)

Answer 15

1. synthesis only by animals as liver , meat , eggs “ not in plant “

Question 16

list daily requirements from vit B12 (cobalamin)

Answer 16

1-3 microgram / day

Question 17

liver stores vit B12 enough for …….

Answer 17

6 years

Question 18

absorption of vit B12 need ………..in the stomach and ……..

Answer 18

acid hydrolysis
intrinsic factor (glycoprotein)

Question 19

-intrinsic factor secreted by ……….of the stomach
- absorbed only in ……..

Answer 19

-parietal cell
- ileum

Question 20

……… transports B12 to liver & tissues

Answer 20

transcobalamin

Question 21

what’s the only water soluble vitamin can be stored in liver for 6 years ?

Answer 21

vit B12 (cobalamin)

Question 22

list forms of vit B12(cobalamin)

Answer 22

1. methyl cobalamin : storage form in the cytoplasm
2. 5-deoxy adenosyl cobalamin : storage form in mitochondria
3. cyanocobalamin : inactive form
4. hydroxocobalamin

Question 22

list forms of vit B12(cobalamin)

Answer 22

1. methyl cobalamin : storage form in the cytoplasm
2. 5-deoxy adenosyl cobalamin : storage form in mitochondria
3. cyanocobalamin : inactive form
4. hydroxocobalamin

Question 23

list functions of vit B12 (cobalamin)

Answer 23

1. regeneration of methionine from homocysteine .
2. methyl malonyl CoA isomerase

Question 24

illustrate the reaction in which vit B12 regenerate methionine from homocysteine

Answer 24

Methyl cobalamin is bounded* in cytoplasm* to methyl transferase to convert :
-homocysteine to methionine
- methyl tetrahydropholate to tetrahydropholate

Question 25

what’s the relation between methyl malonyl CoA and cobalamin

Answer 25

deoxy adenosyl-cobalamin is bounded * in mitochondria * to methyl malonyl CoA isomerase to convert :
L-methyl malonyl CoA to succinyl CoA

Question 26

vit B12 important in normal function of the ……. via its role in synthesis of ….. and maturation of developing …… in the bone marrow

Answer 26

• nervous system
• myelin
• RBCs

Question 27

vit B12 is a cofactor in ……. synthesis and in both …..& …… metabolism .

Answer 27

• DNA
• fatty acid & amino acid

Question 28

illustrate the folate trap or methyl trap

Answer 28

1. it occur due to deficiency of vit B12
2. methyl can’t transfer from folic acid to vit B12 to convert homocysteine to methionine
3. folate is trapped in the N5-methyl form
4. the methylated form can’t be converted directly to other forms of THF
5. the levels of the other forms of one carbon units dec
6. will lead to impaired purine and pyrimidine synthesis
7. impaired DNA synthesis and prevent of cell division

Question 29

list causes of vit B12 deficiency

Answer 29

1.long term vegetarian
2. malabsorption due to dec intrinsic factor as :
- gastrectomy
- atrophic gastritis
- achlorhydria
3. autoimmune destruction of the gastric parietal cells

Question 30

list symptoms of vit B12 deficiency

Answer 30

” pernicious anemia “
1. megaloblastic anemia ‘ macrocytic’ :
impaired DNA synthesis and prevention of cell division with the accumulation of immature erythrocytes in the circulation
2. neurological manifestations :
- itching sensation
- memory loss
- peripheral neuritis
- due to progressive demylination of nervous tissue & 2ry to deficiency of methionine leading to defective methylation.

Question 31

list ttt of vit B12 deficiency

Answer 31

1. initiated with both folic acid & vit B12 to prevent neurological manifestations dt vit B12 deficiency
2. cyanocobalamin intramuscular injection NOT by oral supplementation because of lack of intrinsic factor