Vitamins - What They Do Trivia Quiz

Answer: Carrying out translation of proteins

Vitamin A vitamers are characters by polyunsaturated hydrocarbon chains. Vitamin A is usually called retinol, but retinol is just one of the vitamin A vitamers - others being retinal (which is important in vision) and retinoic acid (which is important in gene expression).

Retinal is one component of the light-sensitive pigment rhodopsin, which is found in the retinas of our eyes. When light strikes retinal, it causes a conformational change (due to a stereochemical change in one of its carbon-carbon double bonds), which is transmitted as a nerve impulse and sent to the brain, telling it that light has been detected.

Retinoic acid binds to the retinoic acid receptor on DNA. This binding causes changes to gene expression and is therefore an example of epigenetics. This vitamin A vitamer is believed to be particularly important in the development of epithelial cells (such as skin) and so is a common ingredient of various skin creams aimed at targeting acne or wrinkles.

Answer: Methyl

We take in folic acid (or folate) from food such as leafy vegetables, and we convert it into its active form known as tetrahydrofolate (THF) via a two-step mechanism catalysed by dihydrofolate reductase. THF is an enzyme cofactor which specialises in the transfer of one carbon units, most usually methyl groups.

These methyl groups are important in synthesising the nucleotides which make up DNA. THF may also methylate histone proteins, which is important in gene regulation, but this is more effectively performed by other methyl donors, such as S-adenosylmethionine (SAM).

Answer: ATP

Unlike some other cofactors, ubiquinone can exist stably in its oxidised (no added electrons), partially reduced (one extra electron), or fully reduced (two extra electrons) form. Ubiquinone is one of the electron carriers in oxidative phosphorylation. During this process, there is a free flow of electrons between different protein complexes in the mitochondrial inner membrane, and the energy released during this transfer is used to transport hydrogen ions out of the mitochondrial matrix. These hydrogen ions then may re-enter the mitochondrial matrix by moving down a concentration gradient via a protein called ATP synthase. ATP synthase couples hydrogen ion entry to the synthesis of ATP.

Vitamin K is also involved in the process of blood clotting. Its importance is seen when using the compound warfarin. Warfarin inhibits vitamin K recycling, which has the same effect of having no vitamin K. Warfarin thins the blood and is used in medical treatments.

Answer: Cobalt

Vitamin B12 (also known as cobalamin and several other names) is structurally similar to the porphyrin ring system found in haem proteins such as haemoglobin. Instead of iron, which is found in haemoglobin, vitamin B12 contains a cobalt ion. It acts as a cofactor in many enzymatic reactions, including those rare reactions which involve the "swapping" of alkyl groups with hydrogen atoms on adjacent carbons. Vitamin B12 is also important for brain functionality, as a deficiency can lead to myelin damage, and the progression of Alzheimer's.

A lack of vitamin B12 is associated with pernicious anaemia/megaloblastic anaemia. This is unlikely to arise from a lack of vitamin B12 in our diets, since we only require tiny amounts of this vitamin. Instead, pernicious anaemia is usually caused by a disease which means people do not produce sufficient amounts of intrinsic factor in their stomachs. This intrinsic factor is a glycoprotein that is needed for the uptake of dietary vitamin B12.

Answer: Diplopia

It was known that pellagra was caused by dietary insufficiency. The curative factor (niacin) was discovered in 1937 by D. Wayne Woolley and Conrad Elvehjem. With niacin being a fairly cheap dietary supplement, incidences of pellagra dropped sharply. It is notable, however, that alcoholics have a much reduced ability to absorb this vitamin and so are more susceptible to developing this disease.

Niacin is similar in structure to nicotine (hence the similarity in name). Niacin is metabolised in the body to NAD, an important cofactor in many enzymatic reactions, usually involving dehydrogenase enzymes. This includes pyruvate dehydrogenase, which converts pyruvate (made in glycolysis) into acetyl-coA. Niacin also assists alcohol dehydrogenase, which catalyses the breakdown of alcohol.

Answer: Smooth muscle

Vitamin E is a lipid-soluble vitamin and often carries out its function at the cell membrane. Alpha-tocopherol, one of the biologically active vitamers of vitamin E, activates a protein called protein phosphatase 2A, which removes phosphate groups from another protein called protein kinase C, inhibiting it. Protein kinase C can therefore no longer stimulate the contraction of smooth muscle within the body. Unlike skeletal muscle, smooth muscle contraction is not brought about by conscious thought.

Vitamin E is a reducing agent and so can help to protect the body from antioxidants. At its position in the plasma membrane, vitamin E therefore is important in protecting the lipids in this membrane from becoming damaged by oxidising factors.

Answer: Gluconeogenesis

Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources, and is activated when glucose levels in the blood are low. Pyruvate is the end product of glycolysis, but its carboxylation (catalysed by pyruvate carboxylase and assisted by biotin) is the first stage in converting pyruvate back into glucose. Pyruvate carboxylase activity is regulated by a wide range of factors, many of which are directly dependent on the level of blood glucose.

Biotin specialises in carrying one-carbon units when carbon is in its most oxidised form (i.e. when it exists as carbon dioxide). This is in contrast to tetrahydrofolate, which tends to carry more reduced one-carbon units. In pyruvate carboxylase, the biotin group (which is covalently bound at the enzyme's active site) transfers the carboxyl group to a pyruvate molecule, thus forming oxaloacetate.

Answer: The liver

It is a good rule in biochemistry, when asked where a reaction usually takes place, to say the liver (unless you know otherwise).

Amino acids are obtained following the digestion of dietary proteins, and circulate freely in the blood. Some may be used to immediately synthesise new proteins, while the excess are taken to the liver. At the liver, aminotransferases (assisted by pyridoxal phosphate) transfer the amino group of the amino acid onto a molecule known as alpha-ketoglutarate. This alpha-ketoglutarate, upon gaining this amino group, forms glutamate which is then able to function as an amino group donor.

Answer: It is lipid-soluble

As mentioned, vitamin D is structurally similar to steroids in that it contains more than one hydrocarbon ring structure. The molecular formula tells us that vitamin D is almost entirely carbon and hydrogen. Carbon and hydrogen have very similar electron-attracting abilities (a property known as electronegativity), meaning that hydrocarbons do not form dipoles and so are described as non-polar. Such non-polar compounds are soluble in lipid, but not in water.

Vitamin D exists in two main forms, known as D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D3 can actually be produced in our body with the help of ultraviolet light from the sun. This UV light causes a bond breakage which converts 7-dehydrocholesterol into cholecalciferol. This is why not leaving the house can lead to rickets! The second form, D2, is obtained from yeast and is commonly added to milk and butter as a fortifying agent. Both play an important role in regulating the levels of calcium in the body, and the absorption of calcium into tissues, which is important for bone development.

Answer: A reducing agent

A reducing agent is something which reduces another molecule/compound and, in the process, becomes oxidised itself. Reduction and oxidation are opposites, and are terms used to describe the movement of electrons. If a molecule gains electrons, it is reduced. If a molecule loses electrons, it is oxidised. A nice way of remembering this is by the mnemonic OiL RiG - Oxidation is Loss and Reduction is Gain (of electrons).

As a reducing agent, vitamin C can be seen as opposing oxidation in the body. It is known that oxidation by entities such as free radicals are responsible for ageing. Vitamin C has therefore been claimed by some to be a panacea and something which should be taken in huge doses. One such person was Linus Pauling, the double Nobel Prize-winning scientist. However, our bodies seem limited in the amount of vitamin C they can absorb, as the large amounts of vitamin C taken by Pauling (and others) simply passed out of his body in urine. Still, Pauling lived to the age of 93, so maybe there was method in his madness.