Fat Soluble Vitamins – Lipids

by Kevin Ahern, PhD

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    00:00 The last set of lipid compound I want to talk about are the fat soluble vitamins. Fat soluble vitamins play obviously very important roles within our body. Depicted on the screen you can see four different forms of an interesting vitamin known as vitamin A. Now vitamin A we know has functions in vision and you can see on the bottom the two forms of vitamin A that are associated with vision. This is the so-called aldehyde form of vitamin A called retinal. And you can see the difference between the retinal on the left called the all-trans and the 11-cis retinal on the right, is that the 11-cis has a change from a trans double bond position 11 on the retinal, to the 11-cis position and you can see the bend that has happened within that vitamin A molecule. Now that bend looks to be pretty trivial, but in fact that bend is responsible for everything that we see. In our eyes we have retinal that's associated with nerve endings and when the light from a source hits vitamin A, vitamin A flips from the trans to the cis position, causing this change that you see on the screen, from being a linear side chain to being a bent side chain. That bent is sufficient to stimulate a nerve cell to send a signal to the brain. So because of this bend that you see right here, we're able to see the world that's in front of us. Retinol in the upper left is another form of vitamin A and it's used primarily as storage of vitamin A in the liver. Retinoic acid on the upper right is a very important derivative of vitamin A that's not stored in fact, but is actually used by developing cells in the process of differentiation.

    01:42 Vitamin D is a molecule that is yet another one that's been derived from cholesterol.

    01:49 Now as we look at this on the screen, it doesn't look very much like that sterol backbone that we saw before, but in fact these two forms of vitamin D arise from a cholesterol type derivative by action of ultraviolet light and the action of ultraviolet light on the vitamin D derivative, causes that sterol backbone to actually break and that's why this structure doesn't resemble the sterol that we saw before, even though it actually came from it. Vitamin D plays an important role in modulating various things, including the calcium magnesium balance that's necessary for healthy bones and it also appears to play a very important role in a healthy immune system.

    02:36 Vitamin E is a vitamin about which we actually know relatively little. Vitamin E deficiency for example, is almost never known to occur and vitamin E does have some interesting properties.

    02:49 Now one of the properties that vitamin E has, is that it appears to act as an antioxidant, that is, it prevents oxidation of other things. It is thought that perhaps vitamin E has a protective role in cell membranes to reduce the incidence of oxidation occurring there.

    03:06 On the screen you can see four different forms of vitamin E, alpha, gamma, beta and delta tocopherol. There are four other forms known as the trienol forms of vitamin E, making a total of about eight different forms of vitamin E. Now the alpha-tocopherol that you see in the upper left is the most potent form of vitamin E and is the form that people usually refer to when they call something vitamin E.

    03:32 Last we have vitamin K. Now vitamin K plays an essential role in blood coagulation. Vitamin K helps the blood clotting proteins to bind to calcium. Now this is a reaction of vitamin K in association with an enzyme stimulates, and what they do is they stimulate the modification of glutamic acid residues. Glutamic acid you may remember from the amino acid structures is one that has an R group that has a carboxyl in the R group. Vitamin K stimulated reaction changes that R group, so instead of having one carboxyl group in these blood clotting proteins, it ends up having two carboxyl groups. And the addition of the second carboxyl group in the R group, the glutamic acid of these blood clotting proteins allows it to bind calcium. One carboxyl within the R group is not sufficient for that.

    04:23 This concludes the portion of the lecture relating to the structure of the individual lipid compounds. Future lectures will deal with the metabolism or the way in which each of these molecules is made.

    About the Lecture

    The lecture Fat Soluble Vitamins – Lipids by Kevin Ahern, PhD is from the course Biochemistry: Basics.

    Included Quiz Questions

    1. Vitamin A is essential for vision.
    2. Vitamin C is made from glucose.
    3. Vitamin E helps to stimulate cellular oxidation.
    4. Vitamin K is used in surgery to reduce the likelihood of blood clotting.
    5. Vitamin D is converted to its inactive form by ultraviolet light.
    1. Retinol — light signal detection in the eye
    2. Retinoic acid — cell differentiation
    3. Vitamin D — osteoporosis prevention
    4. Vitamin E — antioxidant and cell membrane protector
    5. Vitamin K — blood clotting process
    1. Retinol
    2. Retinoic acid
    3. Retinal
    4. Tocopherol
    5. Ergocaliciferol

    Author of lecture Fat Soluble Vitamins – Lipids

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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