Steroids and Bile Acids: Cholesterol Synthesis

by Kevin Ahern, PhD

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    00:01 Now cholesterol looks like a lanosterol, as you can see.

    00:03 But you can also see that it is not a simple process of getting from lanosterol to cholesterol.

    00:08 This process requires 19 steps to go from one to the other.

    00:14 And this 19 step process is very energy requiring and demanding. So that early regulation by the HMG-CoA reductase is a very important consideration.

    00:26 Cholesterol if it accumulates, as I noted, won't inhibit its own synthesis.

    00:31 Now cholesterol is an important component of membranes.

    00:35 If we look at our brain, our brain if we would dry the tissue down contains 14% by weight of cholesterol.

    00:43 Cholesterol is very important and it's one of the reasons why our body needs and is using cholesterol; because, we don't have it in our body simply that will cause problem which it's also associated with.

    00:56 So cholesterol in our body is there by three different mechanisms. First, our cells can synthesize it, as I noted, and it can also be stored in the body. And the way the cholesterol is stored this by linking it to a fatty acid and an extra bond through the hydroxyl group on the lower left.

    01:12 Then cholesterol can be called upon and use in the body as necessary.

    01:15 The third way in which cholesterol in our body is through dietary means.

    01:21 And it's those dietary means that can be big variables in how much cholesterol a person gets in.

    01:26 A person who has high cholesterol when they talk to the doctor, the doctor will use it take as a first step in trying to treat that changing the dietary intake of the person to see if they can someway alter the cholesterol level as a result of that.

    01:40 For some people that's all it takes. For others more aggressive means may be required.

    01:45 Now, one of the reasons we worried about the cholesterol is because it's implicated in atherosclerosis. An atherosclerosis has so obviously some very important implications and monitoring cholesterol levels is a very essential part of a modern health regime.

    02:01 The cholesterol is the precursor of steroid hormone and bile acids.

    02:06 So the steroid hormones are made from cholesterol as are the bile acids and of course, as we will see, these play important functions as well.

    02:14 In last cholesterol, like fat, is very water insoluble which means that it can't just go in the blood stream and travel freely.

    02:23 Instead it must move in the blood stream through what are called lipoprotein complexes.

    02:28 And these lipoprotein complexes have names called LDLs, IDLs, VLDLs and HDLs and the DL part stands for density lipoprotein. And the L, I, V, and H stand for Low, Intermediate, Very low and High.

    02:45 So, monitoring these as part of a cholesterol monitoring scheme is a very important consideration.

    02:52 LDLs, as we will see, are considered the "bad" cholesterol and there is a good reason for that.

    About the Lecture

    The lecture Steroids and Bile Acids: Cholesterol Synthesis by Kevin Ahern, PhD is from the course Lipid Metabolism.

    Included Quiz Questions

    1. The five carbon building block units are made starting with acetyl-CoA
    2. Thiolase catalyzes the last step in the process
    3. HMG-CoA reductase is allosterically regulated by the body’s statin molecules
    4. Cholesterol is an activator of its own synthesis
    1. Squalene contains five isoprene units
    2. Geranyl-pyrophosphate contains two isoprene units
    3. Farnesyl-pyrophosphate contains three isoprene units
    4. Lanosterol contains six isoprene units
    1. Bile acids
    2. Prostaglandins
    3. Vitamin A
    4. Vitamin E

    Author of lecture Steroids and Bile Acids: Cholesterol Synthesis

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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