Metabolism 2 Study guide Exam 4 Folate and Water Soluble Vitamins 1 What are vitamins and difference between fat and water soluble Repeating this question since she asks so many times They are micronutrients that must be supplied from the diet Needed for normal function and their absence cause certain symptoms with each one The body can make some but not in appreciable amounts Fat soluble is obviously soluble in fat stored in the body in large amounts so it s not required every day Since it s stored defiency takes a long time to occur Most have precursors and only higher organisms need them Can be toxic at low amounts but still way higher than the UL Water soluble are stored minimally excreted in the urine so defiency can happen much faster Absorbed into blood since water soluble and both simple and complex organisms need Since they aren t really stored they are only toxic at mega doses 100x DRI Folate can have up to 9 different residues with the important ones being pteridine PABA and You need all of these components to form out folic acid and the body can make all of them except pteroic acid Always know the excepts So this is why it must by consumed we can t form pteroic 2 What is the synthesis of folic acid folate glutamic acid KNOW THESE acid 3 How is it absorbed and metabolized Like all other vitamins it is present in food as one type and we need it in another form to absorb For foltate it is in food as polyglutamate and we have to hydrolyze it to monoglutamate This is done via the conjugase enzymes and they depend on zinc So if you are zinc deficient you will have a hard time absorbing foltate Some foods also contain conjugase inhibitors such as legumes lentils oranges and cabbages So a diet high in these is not ideal for folate status So now we have it done to its monoglutamate form Now what This is reduced in the intestinal cells to the active forms THF and DHF It is half stored in the liver as THF those 4 What are the functions of folic acid Like all the B vitamins folic acid is a coenzyme involved in energy production Specifically the reactions that involve carbohydrate transfers in the form of methyl use folic acid There are three metabolites that participate in these reactions that you will have to know Learn One very important reaction is the resynthesis of methionine from homocysteine Homocysteine is formed from the breakdown of methionine used for epinephrine synthesis If this builds up it can be toxic to the body So folate as THF and vitamin B12 are used to regenerate methionine It starts with 5 methyl THF acting with vitamin B12 to form methylcobalamin So it is simply passing the methyl group to the vitamin B12 The 5 methyl THF loses the methyl and becomes THF This is will resynthesized back the 5 methyl THF Methylcobalamin then will transfer this methyl group to homocysteine to reform methionine This is done via methionine synthase very simple to remember it synthases methionine Now to quickly go over how methionine breaks down to homocysteine Methionine acts with a transferase to form SAM Then SAM will give its methyl away to form SAH then finally homocysteine It is also used in the synthesis of DNA and RNA and the metabolism of some amino acids glycine to serine by donating a methyl group histidine 5 methyl THF is always the starting coenzyme Glycine to serine depends on the tissue of which amino acid will form predominantly 5 What are the sources of folate This is widespread in green vegetables oranges organ meats and yeast Some things to note are it is higher in raw foods heating and cooking destroys folate 6 What does a deficiency lead to The DRI is measured as dietary folate equivalents or DFE A DFE is equal the food folate plus 1 7xug of synthetic folate I would just know what a DFE is in case she asks A deficiency can arise from prolonged cooking since cooking destroys folate and metabolism problems And alcoholics of course Drugs that interact with folate metabolism are methotrexate this is a type of chemotherapy and anticonvulsants If you are vitamin B12 deficient then this increases your risk Now what does it lead to A deficiency will lead to an altered shape and function to the RBC Termed megaloblastic macrocytic anemia In women folate is very important in neural tube development of the fetus Without folate the spinal cord will not develop correctly and can protrude from the body called spina bifida 7 How do we assess the levels of folate can get a short term status Looking at the RBC folate levels we can get a long term status and looking at the plasma levels we One thing to note though is that folate levels depend on vitamin B12 Called the methyl folate trap all this is saying is that if you are deficient in B12 you can t form THF Remember from the methionine resythesis reaction that 5 methyl THF acts with B12 to form THF and methylcobalamin Without B12 we can t form THF which if you recall is the active form of folate Cobalamin B12 1 What is the active form of this vitamin The forms of vitamin B12 are also known as corrinoids and there are multiple forms They all have 4 rings surrounding the cobalamin There are many forms The two active forms are 5 deoxyadenosylcobalamin which has 4 deoxys and methylcobalamin which has 4 methyl s All the other forms can also be converted into these 2 How is it absorbed This vitamin has the most complicated absorption So first the pepsin releases the cobalamin from its ring structure and the cobalamin binds to an R protein and then travels to the small intestine In the first part the duodenum the R protein is hydrolyzed and then the cobalamin binds then something called Intrinsic Factor which is made in the stomach Now it gets absorbed in the ileum where the receptors are Once the cobalamin is in the blood it then binds to either Transcobalmin 1 2 or 3 Although 2 is the most common one And then it is stored in the liver mostly and some in the muscles Although a water soluble vitamin it is stored better than most others so deficiency take several years to occur Bacteria in the intestinal also can make a little 3 What are the sources This vitamin is only in animal products so if you are a vegetarian you need to get your B12 from supplements It is retained fairly well from cooking but a great deal is lost from the process of milk pasteurization 4 What are the functions of B12 THF to homocysteine normal used in energy metabolism Going back to the methionine resynthesize B12 is needed to transfer the methyl form 5
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