Lipid Metabolism: Steroids & Bile Acids

by Kevin Ahern, PhD

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    Cholesterol is a molecule, that a lot of people say "Can’t live with it, can’t live without it". I hope in this lecture you will see that the latter is true. In this lecture I will go through the synthesis of ketone bodies and cholesterol and we will see how they are related to each other. We will talk about cholesterol in health and also talk about how the steroids themselves are synthesized and how bile acids are involved. And these are all molecules that are related to cholesterol. Now, in the synthesis of molecules like cholesterol, we start with a very simple thing. The simple thing that we start with is the same thing that we started with in fatty acids synthesis and that's acetyl-CoA. In cholesterol synthesis we see that it's pathway overlaps with the pathway of making ketone bodies and that's the first thing that we are gonna talk about. So in the synthesis of ketone bodies in cholesterol 2 acetyl-CoAs are joined together to make a 4 carbon molecule called acetoacetyl-CoA. This reaction is catalyzed by the reversal of the last step of beta oxidation of a fatty acid. Now you may recall from that presentation that the enzyme thiolase catalyzes the breakdown or the cutting off of two carbon pieces from each of the fatty acid chains. When the fatty acid chain has 4, there are 2 molecules of acetyl-CoA that are produced and if you run that reaction backwards, the 2 molecules of acetyl-CoA can be made into the molecule that you see here, acetoacetyl-CoA. In the next step of the reaction, you see that 2 more carbons are added from another acetyl-CoA to make a 6 carbon molecule called HMG-CoA. This molecule, as we will see, is a branch point between the synthesis...

    About the Lecture

    The lecture Lipid Metabolism: Steroids & Bile Acids by Kevin Ahern, PhD is from the course Lipid Metabolism. It contains the following chapters:

    • Mevalonate Pathway I
    • Ketone Body Synthesis
    • Mevalonate Pathway II
    • Cholesterol Synthesis
    • Movement of Cholesterol
    • Receptor-Mediated Enocytosis
    • Steroid Hormone Metabolism

    Included Quiz Questions

    1. ...starts with the same molecules as cholesterol synthesis.
    2. ...begins with acetoacetate.
    3. ...ultimately produces an 8-carbon product.
    4. ...involves squalene.
    1. ...acetone.
    2. ...acetyl-CoA.
    3. ...beta-hydroxy-butyryl-CoA.
    4. ...acetoacetate.
    1. Acetyl-CoA
    2. Acetone
    3. Fructose
    4. Glucose
    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.
    1. ...HDLs are the smallest.
    2. ...LDLs carry the most fat.
    3. ...chylmicrons are made by the liver.
    4. ...VLDLs are the densest.
    1. ...progestagens are the precursors of all of the other ones.
    2. ...synthesis of androgens from estrogens requires aromatase.
    3. ...mineralocorticoids are precursors of all of them except progestagens.
    4. ...glucocorticoids include aldosterone.

    Author of lecture Lipid Metabolism: Steroids & Bile Acids

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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    Very concise and straight-forward
    By Nico D. on 10. February 2017 for Lipid Metabolism: Steroids & Bile Acids

    Great lecture! I hope that the rate limiting steps in the reactions can be highlighted in the presentations as these are common exam questions :)