Describe the chemical properties of vitamins & understand how this influences their metabolism
As you should (hopefully) know by now, some vitamins are fat-soluble (A, D, E and K), whereas others are fat-soluble (all of the other vitamins). Fat-soluble vitamins can be stored in lipids and in the liver for a long time, whereas there is generally very little storage for water-soluble vitamins. As such, it is easier to have too much of a fat-soluble vitamin than too little, and it is easier to have too little of a water-soluble vitamin than too much.
Fat-soluble vitamins are absorbed with lipids (see here for information on how fats are absorbed). Once in the blood, they can be transported in lipoproteins or attached to specific binding proteins (e.g. vitamin D binding protein, or VDBP, transports vitamin D around the blood). Water-soluble vitamins are generally absorbed via specific transporters (as mentioned here). They do not need to be bound in order to be transported around the blood.
Describe metabolic pathways of specific vitamins
Describe the functions of specific vitamins
Outline the biological effects over under/over supply of different vitamins
- Vitamin B9 (Folate) (also covers some basic information on overdose/deficiency symptoms of other vitamins)
- Vitamins B12 (Cobalamins) and B6 (Pyridoxine)
- Vitamins A and D
- Vitamins C and K
Now for the fun facts that weren't covered in these posts!
Vitamin A
When we take up β-carotene (the plant form of vitamin A), the first thing our enterocytes do is convert it into an animal form. β-carotene is converted into retinal. Retinal can then be converted into retinoic acid for storage, or converted into retinol. Retinol can then be converted into retinol ester and transported around the body in chylomicrons. (Retinol ester also serves as a storage form in some tissues, such as liver.) There is also a retinol-binding protein, or RBP, which can transport retinol around the blood.
Another fun fact about vitamin A is that both excess and deficiency during pregnancy are teratogenic. So make sure you're getting the right amount- no more, no less.
Vitamin D
Uhhh I don't think there's much I can say here that I didn't say in this earlier post. Oh, hang on, there is one fun fact I can tell you: D3 is converted into calcidiol in the liver, and into calcitriol in the kidney. Also, as mentioned earlier, it can be transported around the blood by vitamin D binding protein (VDBP). Yay I guess? Vitamin D plays a lot of roles in calcium metabolism, but apparently we'll be learning more about that in the calcium lecture. (The calcium/vitamin D link also got a cameo appearance in this post.)
Vitamin E
Yay, here's a vitamin that I haven't spoken about before! Vitamin E is part of a family of tocopherols. The most common tocopherol, which also happens to be the one with the highest biological activity, is α-tocopherol. Like with vitamins A and D, vitamin E has its own transport protein: α-tocopherol transport protein (α-TTP).
Vitamin E's main role is as a lipid-soluble antioxidant (vitamin C is a water-soluble antioxidant). It is very rare to be deficient in vitamin E, but consequences of deficiency include impairment of fertility, peripheral neuropathy and anaemia due to diminished red blood cell life span. (Without vitamin E, cell membranes are more prone to oxidative stress.) In the rare event of toxicity, increased bleeding can occur.
Vitamin K
Don't think there's anything I can say here that I haven't said here.
Vitamin B1 (Thiamine)
Another vitamin that I haven't spoken about in much detail! It can act as part of a coenzyme (thiamin pyrophosphate, or TPP) in carbohydrate and amino acid metabolism, or it can play a role in thymine production. Mild deficiency symptoms include GI complaints and weakness, moderate deficiency symptoms include peripheral neuropathy, mental abnormalities and ataxia, and severe deficiency results in beri-beri, which is characterised by severe muscle weakness, muscle wasting, delirium and memory loss.
Vitamin B2 (Riboflavin)
B2 is part of FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide). Both of these play a large role in redox reactions. Deficiency symptoms include inflammation of the lining of the mouth and tongue, dry and scaling skin, mental depression and forgetfulness.
Vitamin B3 (Niacin)
Niacin is a part of NAD and NADP. The liver can synthesise niacin from tryptophan in a reaction requiring B6, but this is an extremely slow process that is generally insufficient. A serious deficiency of niacin causes pellagra, which is characterised by "the four Ds": diarrhoea, dermatitis, dementia and death.
Vitamin B5 (Pantothenic Acid)
B5 is a part of acetyl CoA, which is required for stuff like the TCA cycle. Deficiencies are extremely rare, but may lead to metabolic deficiencies, paresthesia (pins and needles) and neurological symptoms (due to disordered synthesis of acetylcholine, which is basically just acetyl CoA + choline).
Vitamin B6 (Pyridoxine)
See here.
Vitamin B7 (Biotin)
Biotin is a part of several ATP-dependent carboxylase enzymes, such as pyruvate carboxylase. It is also a coenzyme for fatty acid synthesis and gluconeogenesis.
Vitamin B9 (Folic Acid)
See here. The active metabolite of folic acid is THF, or tetrahydrofolate.
Vitamin B12 (Cobalamin)
See here.
Vitamin C (Ascorbic Acid)
See here. One fun fact is that vitamins C and E can "recharge" each other.
Vitamin E's main role is as a lipid-soluble antioxidant (vitamin C is a water-soluble antioxidant). It is very rare to be deficient in vitamin E, but consequences of deficiency include impairment of fertility, peripheral neuropathy and anaemia due to diminished red blood cell life span. (Without vitamin E, cell membranes are more prone to oxidative stress.) In the rare event of toxicity, increased bleeding can occur.
Vitamin K
Don't think there's anything I can say here that I haven't said here.
Vitamin B1 (Thiamine)
Another vitamin that I haven't spoken about in much detail! It can act as part of a coenzyme (thiamin pyrophosphate, or TPP) in carbohydrate and amino acid metabolism, or it can play a role in thymine production. Mild deficiency symptoms include GI complaints and weakness, moderate deficiency symptoms include peripheral neuropathy, mental abnormalities and ataxia, and severe deficiency results in beri-beri, which is characterised by severe muscle weakness, muscle wasting, delirium and memory loss.
Vitamin B2 (Riboflavin)
B2 is part of FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide). Both of these play a large role in redox reactions. Deficiency symptoms include inflammation of the lining of the mouth and tongue, dry and scaling skin, mental depression and forgetfulness.
Vitamin B3 (Niacin)
Niacin is a part of NAD and NADP. The liver can synthesise niacin from tryptophan in a reaction requiring B6, but this is an extremely slow process that is generally insufficient. A serious deficiency of niacin causes pellagra, which is characterised by "the four Ds": diarrhoea, dermatitis, dementia and death.
Vitamin B5 (Pantothenic Acid)
B5 is a part of acetyl CoA, which is required for stuff like the TCA cycle. Deficiencies are extremely rare, but may lead to metabolic deficiencies, paresthesia (pins and needles) and neurological symptoms (due to disordered synthesis of acetylcholine, which is basically just acetyl CoA + choline).
Vitamin B6 (Pyridoxine)
See here.
Vitamin B7 (Biotin)
Biotin is a part of several ATP-dependent carboxylase enzymes, such as pyruvate carboxylase. It is also a coenzyme for fatty acid synthesis and gluconeogenesis.
Vitamin B9 (Folic Acid)
See here. The active metabolite of folic acid is THF, or tetrahydrofolate.
Vitamin B12 (Cobalamin)
See here.
Vitamin C (Ascorbic Acid)
See here. One fun fact is that vitamins C and E can "recharge" each other.
No comments:
Post a Comment