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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, will 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. It is an important component of the cell membranes.
    2. HDL is considered harmful to the human body.
    3. High LDL levels decrease the risk of atherosclerosis.
    4. Cholesterol is an essential fatty acid.
    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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