Vitamin Deficiency & One Carbon Unit Metabolism

Question 1

Enzymes requiring thaimin & def diseases

Answer 1

PHD, a-ketoglutarate dehydrogenase (osidative decarboxylation), transketolase, branched chain ketoacid dehydrogenase
Wernike-Korsakoff (psychosis & encephalitis), acute def in alcoholics
Beriberi (wet & dry)

Question 2

Thiamin forms coezyme ….. by ………

Answer 2

TPP
ATP dependant reaction in brain & liver

Question 3

Mention tests for thiamin status

Answer 3

Blood thiamin
Urine thiamin
Erythrocyte transketolase activity
Thiamin pyrophosphate effect
Blood pyruvate & lactate

Question 4

Biochemical basis & CP of Pyruvate dehydrogenase deficiency

Answer 4

Pyruvate isn’t converted to acetylCoA, production of citrate is limited thus TCA cannot proceed. An energy deficit occurs
CP, lactic acidosis due to divergence of pyruvate to other pathways
Neurological form contributes to hypotonia, poor feeding, lethargy, structural brain abnormalities leads to mental retardation, microcephaly, blindness, spasticity.

Question 5

Treatment of PDH def

Answer 5

Dietary restriction of carbs
Correction of acidosis

Question 6

Niacin chemical structure is ……

Answer 6

Pyridinine 3-carboxylic acid

Question 7

Mention sources of niacin

Answer 7

Food, unrefined grains, milk, lean meat.
Tryptophan

Question 8

Mention a therapeutic use of niacin

Answer 8

Lowers plasma cholesterol and TAGs as it strongly inhibits lipolysis in adipose tissue, thus dec circulating FFAs

Question 9

Symptoms and causes of pellagra

Answer 9

S, dermatitis, diarrhea, dementia, death
C, diet poor in tryptophan and niacin, defective absorption as Hartnup disease, B6 def, carcinoid tumour.

Question 10

Describe chemical composition of folic acid

Answer 10

Pteridine ring +pABA+glutamate

Question 11

Describe the reaction of folate activation

Answer 11

By two sequential steps both are NADPH+H+ rewuiring enzymes: folate reductase and dihydrofolate reductase.

Question 12

Sulfa drugs inhibit ….. while trimethoprim inhibits …..

Answer 12

Folic acid synthesis
Dihydrofolate reductase

Question 13

Mention the metabolic role of tetrahydrofolate

Answer 13

Carrier of one carbon unit for synthesis of choline, serine, glycine, methionine, purines.

Question 14

List Most reduced, intermediate and most oxidized one carbon units respectively

Answer 14

Methyl
Methylene
Formyl formimino methenyl

Question 15

One carbon uits can be carries by …

Answer 15

THF
SAM

Question 16

CO2 is carried by …

Answer 16

Biotin

Question 17

One C units are linked to THF at

Answer 17

N5
N10
Both

Question 18

Interconversion of 1C unit occurs by enzymes….&….

Answer 18

NAD-dehdrogenase
NADP-reductase

Question 19

Sources and fate of methylene group

Answer 19

S, b-carbon of serine, glycine by glycine cleavage system
F, oxidized to methenyl-THF, reduced to methyl-THF, thymidylate synthesis.

Question 20

Sources and fate of methenyl group

Answer 20

S, histidine –>figlu–>5-formimino THF–> 5,10 methenyl THF
Oxidation of methylene THF
F, hydrolysed to N10 formyl THF

Question 21

Sources and fate of formyl group

Answer 21

S, activation of free formate by ATP (Formyl THF synthetase), hydrolysis of methenyl THF, Tryptophan catabolism.
F, synthesis of C2, C8 in purines

Question 22

Sources and fate of methyl THF

Answer 22

S, by reduction of methylene THF catalyzed by methylene THF reductase (NAD-linked)
Fate, vit B12 coenz, accept CH3 to form methylcobalamin then transfer it to homocysteine to form methionine

Question 23

Explain methyl trap

Answer 23

Def of B12 in which THF is converted to methyl THF which thereafter has no way of being metabolized and serves as a sink of THF that causes a subsequent deficiency of folate.