Metabolism 2 Study guide Exam 4 Riboflavin B2 1 What is the active form Riboflavin is the basis of two other coenzymes that we have covered many times in metabolism 1 FAD and FMN It is another of the B vitamins or water soluble Riboflavin is a cyclic molecule that when phosphorylated forms FMN and then FAD FAD is the electron carrier in the citric acid cycle and produces ATP in the electron transport chain FAD is flavin adenine dinucleotide and FMN is flavin mononucleotide 2 What are the sources it will be there Riboflavin is widespread is milk and dairy products and in most meats If grains are enriched then This B vitamin is very light sensitive and UV light will easily destroy it It is stable is cooking and processing though 3 How is it absorbed digested transported and stored Like every other vitamin gone over first the protein part have to be removed or in other words it has to be hydrolyzed Good ole HCl helps this process to remove the proteins So if it is eaten as FAD and FMN it is first hydrolyzed and the riboflavin must be in its free form to be absorbed This is done by the two enzymes FAD pyrophosphatase and FMN phosphatase HCl only removes the proteins Now that we have are free riboflavin it is absorbed via active transport mostly Once it enters the mucosal cells and this is phosphorylated back to FMN via the enzyme flavokinase After the mucosal layer at the serosal layer some of that FMN we just formed returns back to free riboflavin and is then shunted to the liver It is stored as FAD So it seems there was some unnecessary back and forth Free riboflavin form FMN in the mucosal layer then went back to riboflavin in the serosal and then goes to FAD in the liver The body gets confusing at times 4 What are the functions of riboflavin Its main function is as an electron carrier as FAD It is reduced in the TCA cycle to FADH and then oxidized in the electron transport chain to provide the potential to produce ATP It also helps to reduce glutathione to GSH 5 What is the deficiency of riboflavin alcoholics and elderly Populations most likely to be deficient in this vitamin are those that are lactating or pregnant You will start to see a pattern in these populations Alcoholics are at risk for all deficiencies as are elderly s as they generally have poor nutrition Pregnant women need more of the same vitamins for the fetus handle digestion and the absorption Those in some clinical situations also have a risk simply because their body might not be able to Infants with hyperbilirubinemia on photo therapy should be given extra riboflavin The photo therapy destroys it if you remember that it is very light sensitive When a deficiency does develop it will lead to glossitis and stomatitis skin changes and peripheral neuropathy 6 How to assess it and what is the DRI The best way to assess one s status for riboflavin is to look at their activity of the RBC glutathione reductase because as you recall FAD is required for this reaction FAD will convert the GSSG with the help of NADPH to GSH so without riboflavin that means no FAD and no GSH They measure the reaction based on if another reactant NADPH is used This is easy to measure Niacin B3 1 What is the active form acid or nicotinamide in its active form Niacin forms the other electron carrier in ATP production NAD It is either referred to as nicotinic When one of these forms attaches to a ribose and adenosine you get a NAD Then this is what is reduced in the TCA cycle to NADH and this is oxidized to NAD in the electron transport 2 What are the sources chain sources Niacin is best found in meat and fish It is in its free form nicotinamide here so these are the best Remember that our body always absorbs the free form for everything Meat and fish are the best sources but we can also get niacin from cereals legumes seeds coffee and tea to an extent Corn is noted as a poor source so that means that you should defiantly know that It is poor because it is low in tryptophan this can form niacin in the body and the niacin in the corn is unavailable Lime water can free the niacin for us though Now to what we can make The body can form niacin from the amino acid tryptophan It takes 60mg of tryptophan to form 1mg niacin This is referred to as a niacin equivalent 3 What are the functions of niacin Niacin helps around 200 enzymes to function because all B vitamins are coenzmyes As NAD it works in metabolism to pick up electrons by being reduced to NADH NAD is present is glycolysis the TCA cycle and beta oxidation As NADH it is now in its reduced form and this transfers the electrons to the electron transport NADP is present in the hexose phosphate shunt and in the maltate shuttle system That is all chain that you need to know about NADP NADHP is required for fatty acid synthesis to reduce cholesterol to make DNA precursors and it is one of the reactants in that glutathione reaction that is talked about so much Know that it is a reducing agent for all the above 4 What does a deficiency lead to The DRI is 14 NE day or niacin equivalents 1 NE is equal to either 1 mg niacin 60 mg tryptophan or 6000 mg protein Remember that 60 mg tryptophan can form 1 mg niacin And the assumption is if you have 6000 mg protein you probably have 60 mg tryptophan in there 1000 mg 10 mg tryptophan finally Death A deficiency will lead to pellagra which is the famed 4D s Dermantitis Diarrhea Dementia and For people at risk we have people with increase energy requirements One drug does interfere with niacin and that is isoniazid so defiantly know that If you have a deficiency in tryptophan or a problem with its metabolism this will put you at an increased risk The example for this is Hartnup disease 5 Is there a toxicity Niacin in excessive is used to lower lipid levels Namely LDL VLDL and increase HDL The only side effect with this is it causes the sudden release of histamine which is an inflammatory marker This causes flushing of the skin and will lead to itching and gastrointestinal problems 6 How do you assess it Simply look at the urinary excretion of N methyl nictotinamide after a 50 mg test dose Based on this number you can determine their level Below 0 5 is considered deficient 0 5 1 59 is marginal and above 1 6 is adequate Folate B9 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 …
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