Water Soluble Vitamins

Question 1

Thiamine characteristics?

Answer 1

Active form: thiamine pyrophosphate (TPP)

TPP is involved in alpha-keto acids

Question 2

What are the two types of thiamine transporter?

Answer 2

THTR 2 (low or normal concentrations, active transport)

THTR 1 (high concentration, passive)

Alcohol affects only the THTR 2 carrier mediated transport

Question 3

Thiamine deficiency leads to…

Answer 3

Wet beri-beri (edema and CV problems)

Dry beri-beri (neurological problems)

Wernicke-Korsakoff syndrome: CNS lesions, associated with alcoholism

Question 4

Riboflavin (Vitamin B2)

Answer 4

Is readily destroyed by sunlight

Active forms are FMN (can be reduced to FMNH2) and FAD (can be reduced to FADH2)

Question 5

Riboflavin deficiency

Answer 5

Stomatitis (inflammation of mouth)

Cheilosis (painful cracking of corners of mouth)

Glossitis (inflammation of tongue)

Question 6

Niacin

Answer 6

Active forms: NAD+, NADP+; serve as coenzymes in RedOx reactions

Tryptophan can make NAD, de novo

ADP ribose can help convert NAD to nicotinamide

Question 7

How does niacin help lower LDL and increase HDL?

Answer 7

Decrease in LDL is due to noncompetitive inhibition by niacin on a liver enzyme involved in triglyceride synthesis

This decreased synthesis results in intracellular apo B degradation and decreased secretion of VLDL particles

Question 8

Niacin deficiency characteristics

Answer 8

Pellagra: dermatitis, dementia, diarrhea (3 D’s); also caused by insufficient tryptophan

Hartnup’s dx: affects amino acid transport; an increased need for niacin may lead to its deficiency

Question 9

Biotin

Answer 9

The enzyme biotinidase removes bound biotin from protein (a good thing!)

Deficiency of biotinidase results in increased fatty acid production; also, body becomes biotin deficient

Question 10

Biotin deficiency

Answer 10

Caused by defects in reutilization (not diet); see biotinidase

Absence of holocarboxylase synthase enzyme causes multiple carboxylase deficiency

Question 11

Panthothenic acid

Answer 11

Is a component of coenzyme A (CoA)

Question 12

Folic acid

Answer 12

Consists of pteridine attached to PABA and a glutamic acid

Monoglutaminated folic acid is taken up by the reduced folate carrier (RFC) in the intestine

Question 13

Formation of tetrahydrofolic acid (THF) is inhibited by…

Answer 13

Methotrexate, a treatment option which inhibits the dihydrofolate reductase

Also, anything affecting vit B12 production will also affect folate production

Question 14

Megaloblastic anemia

Answer 14

Is caused by diminished synthesis of purines and thymidine, leading to the inability of cells to both divide and make DNA

Macrocytic RBCs are seen (no cell division, so the cells keep growing)

Transulfuration pathway needs vit B6

Question 15

Spina Bifida

Answer 15

Is caused by a C -> T substitution (valine for alanine)

May account for neural tube defect

Question 16

Histidine load test is used for?

Answer 16

Measuring FIGLU and seeing if there is a deficiency in folic acid

If FIGLU is high in the urine sample, THF is therefore low, because it would have converted the FIGLU into other things (if things were normal, FIGLU would not be high in the urine)

Question 17

Dietary Vitamin B12 overview

Answer 17

B12 binds to transcobalamin I in the stomach which then travel to the intestine and are then destroyed by pancreatic proteases

The freed B12 then binds to intrinsic factor (IF), and then are absorbed by ileum and then carried by transcobalamins

Question 18

Absorption and transport of Vit B12

Answer 18

B12 is bound by transcobalamin II when transported to the tissues

Question 19

Dx and deficiencies associated with B12

Answer 19

Crohn’s Dx: affects ileum so that there is an impairment of bile acid and B12 absorption

Dx sx: megaloblasic anemia, pernicious anemia (if lacking IF), homocystinuria (homocysteine does not convert to methionine) and methylmalonic aciduria

Question 20

Methylmalonic aciduria characteristics

Answer 20

Propionyl CoA —biotin—> methylmalonyl CoA –vit B12–> succinyl CoA -> citric acid cycle and gluconeogenesis

If vit B12 is deficient, MM CoA cannot convert to succinyl CoA; thus, MM CoA builds up (bad!)

Question 21

Pyridoxine (Vit B6)

Answer 21

Pyridoxal phosphate (PLP) is the active form

PLP is essential for transaminase rxns and the synthesis of the NTs (serotonin, epi, norepi and GABA)

PLP also required for synthesis of alanine (precursor of heme)

Question 22

Vitamin B6 deficiency

Answer 22

Causes hypoglycemia due to impairments of glycogenolysis and gluconeogenesis

May cause sideroblastic microcytic anemia

Question 23

How to test for vit B6 defiency

Answer 23

Tryptophan load test

Trp usually ends up forming alanine, because PLP cleaves kynurenine. If PLP is deficienct, it, instead, leads to an increase in xanthurenic acid, a measurable quantity after a load test.

Question 24

Ascorbic acid / Vitamin C

Answer 24

Important for collagen formation

Deficiencies lead to weak collagen, bleeding gums, poor wound healing and petechiae