Copy of Chapter Six

8/2/2019 Copy of Chapter Six

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The active coenzyme form of biotin is biotin itself. It is a coenzyme involved incarboxylation reactions in the metabolism of

fats , carbohydrates and protein .


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RDA FORBiotin


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Daily needs for adults: 30 g/day

Deficiency of biotin:


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Deficiency of biotin is rare in human because it is

widely distributed in foods. But deficiency of biotin occurs in consuming large amounts of rawegg white, because egg white contains aglycoprotein avidin which binds to biotin andprevent biotin absorption. Also intakesulphonamide drugs or oral antibiotics forprolonged periods, that inhibit the growth of intestinal bacteria, eliminate this source of biotinand lead to biotin deficiency.

The biotin deficiency leads to dermatitis, loss of hair, decrease in weight, sleepiness, depress andnausea.

Lipoic acid:


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Lipoic acid is found in yeast, liver, and thecompound occurs widely in nature. Lipoicacid exists in oxidized and reduced form.

Lipoic acid functions as a coenzyme inpyrovate dehydrogenase multi enzyme complex and - ketoglutarate dehydrogenasemulti enzyme complex.


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Lipoamide contains sulfurs that can be reversibly oxidized or reduced.


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Deficiency of lipoic acid:


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A deficiency of lipoic acid usually does notoccur because it is widespread in the nature.

Folic acid:


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Folic acid is widely distributed in the word. Agood source of this vitamin are liver, kidney,green leafy vegetables, tomatoes, potatoes,

Folic acid is converted to its active coenzymetetrahydrofolate (THF) or (FH4).

F l t


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FolateSources


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positions 7 and 8 carry hydrogens in dihydrofolate (DHF) positions 5 8 carry hydrogens in tetrahydrofolate (THF)

Tetrahydro folate act as a carrier of one


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carbon unit (may be methyl -CH3, methylene

-CH2, formyl -CHO, formate- COOH.)during metabolism.FH4 is used in the synthesis of purines and

pyrimidines , and therefore for the formation of DNA and RNA in all cells includingmaturing blood cells- synthesis of RBC andWBC.Also FH4 is needed for the synthesis of aminoacid methionine .

Deficiency of folic acid:


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Folic acid deficiency leads to megaloblastic

anemia , caused by decreasing synthesis of purine and pyrimidine , which inhibits DNA synthesis . This leads to change in size andshape of the nuclei and slower maturation of red blood cells , causing production of abnormality large red blood cells with fragile membranes . Also folate deficiency leads to

glossistis and gastero intestinal disorders .Folic acid is especially necessary for childrenand pregnant women

Folate


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Folate deficiency results in macrocytic anemia.

Cobalamin (Vitamin B12)


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Dietary source of vitamin B12 are of animalorigin and include meat, eggs, milk,fish,.Vitamin B12 is absent in plant foods.

Human obtain small amounts of this vitaminfrom their intestinal flora.


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Cobalamine exists in three forms that differ in the group attached tocobalt. The active coenzyme forms of vitamin B12 are methyl

cobalamine and deoxyadenosyl cobalamine


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Cobalamin (Vitamin B12) is a coenzyme forenzymes that transfer methyl groups andproduce red blood cells.Vitamin B12 is the only water soluble vitamin

that is stored in significant amounts in theliver, bone marrow and other tissues.

vitaminB 12 coenzyme-dependent enzymes


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153

: Murray et al, 1996


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Deficiency of vitamin B12:


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Deficiency of this vitamin is not observedbecause it is widespread in foods of animal

origin. Vitamin B12 deficiency causes folatedeficiency (because the generation of FH4depends on the presence of Vitamin B12),therefore, all the manifestation of folatedeficiency are also seen.


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Also the deficiency causes pernicious anemia,


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a disease that is characterized by the presenceof large, immature of red blood cells in theblood. Symptoms include a sore tongue,weight loss, mental and nervous disorder. The

damage to the central nervous system caneven cause demyelination of the peripheralnerves in the arms and legs. Eventually, thiscan progress to the spinal cord.


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Metabolic Pathways Involving BVitamins


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Controversy: Vitamin Supplements: Do theBenefits Outweigh the Risks?


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Which is the best source?

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