folic acid and vit B12 Flashcards
def the vitamins
-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
list causes of vitamin deficiency
- inadequate dietary intake or malabsorption : e.g. biliary obstruction , pancreatitis
- dysfunction or absence of proteins required to absorption , transport , activation or utilization
- inc excretion as in kidney disease
- drug related :
- antibiotic therapy kills intestinal microorganisms cause vit K deficiency
- anti TB drug isoniazid can dec vit B6 absorption
classify vit B family
- energy related :
- thiamine (B1)
- biotin (B7)
- riboflavin (B2)
- niacin (B3)
- pantothenic acid (B5) - hematopoietic :
- folic acid (B9)
- vit B12 - others :
pyridoxine (B6)
list chc of fat soluble vitamins
- fat soluble
- water insoluble
- require the presence of lipid and bile salts for absorption
- require carrier protein
- stored in liver
- not excreted
- occur deficiency only when stores are depleted
- occur toxicity
- ttt of deficiency = single large dose
- example = vit A D E K
list chc of water soluble vitamins
- fat insoluble
- water soluble
- simple absorption
- not require carrier protein
- not storage
- excreted in urine
- deficiency occur rapidly as there is no storage
- toxicity = unlikely
- ttt of deficiency= regular dietary supply
- example = vit C & B complex
illustrate the chemistry of vit B9 ( folic acid) and sources
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”
list daily requirement of vit B9 in :
normal & pregnancy condition
- 400 microgram / day
- 800 microgram / day in pregnancy and lactation
list function of vit B9
- carrier of one Carbon unite “ except CO2”
- synthesis of DNA “ replication “ :
purine & thymine - synthesis of serine & glycine
- synthesis of methionine & choline , methyl (CH3) synthesize methionine from homocysteine “ need vit B12 “
list causes of folate deficiency
- inc rate of cell division e.g. pregnancy , anemia
- poor absorption
- administration of methotrexate as anticancer
- vit B12 deficiency “ folate trap “
what’s the effect of folate deficiency ?
defect cell proliferation due to defect in DNA synthesis
“ megaloblastic anemia , immature RBCs in BM & blood “
what’s the effect of PABA analogs ( sulfa drug ) on vit B9 as antagonist?
-prevent folic acid synthesis by bacteria ( antibiotic )
-inhibit dihydropteroate synthetase
what’s the mechanism of folic acid analogs (methotrexate ) as antagonist ?
competitive inhibit dihydrofolate reductase (used as anticancer)
what’s trimethoprim ?
-folic acid antagonist , act on bacteria only
- inhibit folate reductase & used as antibiotic
illustrate chemistry of vit B12(cobalamin)
- 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 )
illustrate the sources of vit B12 (cobalamin)
- synthesis only by animals as liver , meat , eggs “ not in plant “
list daily requirements from vit B12 (cobalamin)
1-3 microgram / day
liver stores vit B12 enough for …….
6 years
absorption of vit B12 need ………..in the stomach and ……..
acid hydrolysis
intrinsic factor (glycoprotein)
-intrinsic factor secreted by ……….of the stomach
- absorbed only in ……..
-parietal cell
- ileum
……… transports B12 to liver & tissues
transcobalamin
what’s the only water soluble vitamin can be stored in liver for 6 years ?
vit B12 (cobalamin)
list forms of vit B12(cobalamin)
- methyl cobalamin : storage form in the cytoplasm
- 5-deoxy adenosyl cobalamin : storage form in mitochondria
- cyanocobalamin : inactive form
- hydroxocobalamin
list forms of vit B12(cobalamin)
- methyl cobalamin : storage form in the cytoplasm
- 5-deoxy adenosyl cobalamin : storage form in mitochondria
- cyanocobalamin : inactive form
- hydroxocobalamin
list functions of vit B12 (cobalamin)
- regeneration of methionine from homocysteine .
- methyl malonyl CoA isomerase
illustrate the reaction in which vit B12 regenerate methionine from homocysteine
Methyl cobalamin is bounded* in cytoplasm* to methyl transferase to convert :
-homocysteine to methionine
- methyl tetrahydropholate to tetrahydropholate
what’s the relation between methyl malonyl CoA and cobalamin
deoxy adenosyl-cobalamin is bounded * in mitochondria * to methyl malonyl CoA isomerase to convert :
L-methyl malonyl CoA to succinyl CoA
vit B12 important in normal function of the ……. via its role in synthesis of ….. and maturation of developing …… in the bone marrow
- nervous system
- myelin
- RBCs
vit B12 is a cofactor in ……. synthesis and in both …..& …… metabolism .
- DNA
- fatty acid & amino acid
illustrate the folate trap or methyl trap
- it occur due to deficiency of vit B12
- methyl can’t transfer from folic acid to vit B12 to convert homocysteine to methionine
- folate is trapped in the N5-methyl form
- the methylated form can’t be converted directly to other forms of THF
- the levels of the other forms of one carbon units dec
- will lead to impaired purine and pyrimidine synthesis
- impaired DNA synthesis and prevent of cell division
list causes of vit B12 deficiency
1.long term vegetarian
2. malabsorption due to dec intrinsic factor as :
- gastrectomy
- atrophic gastritis
- achlorhydria
3. autoimmune destruction of the gastric parietal cells
list symptoms of vit B12 deficiency
” 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.
list ttt of vit B12 deficiency
- initiated with both folic acid & vit B12 to prevent neurological manifestations dt vit B12 deficiency
- cyanocobalamin intramuscular injection NOT by oral supplementation because of lack of intrinsic factor