• Cholesterol has a molecular formula of C27H45OH. This molecule is composed of three regions (shown in the picture above): a hydrocarbon tail (shown in blue), a ring structure region with 4 hydrocarbon rings (shown in green), and a hydroxyl group (shown in red.).

    The hydroxyl (OH) group is polar, which makes it soluble in water. This small 2-atom structure makes cholesterol an alcohol. The alcohol that we drink, ethanol, is a much smaller alcohol that also has a hydroxyl group (C2H5OH).

    The 4-ring region of cholesterol is the signature of all steroid hormones (such as testosterone and estrogen). All steroids are made from cholesterol. The rings are called "hydrocarbon" rings because each corner of the ring is composed of a carbon atom, with two hydrogen atoms extending off the ring.

    The combination of the steroid ring structure and the hydroxyl (alcohol) group classifies cholesterol as a "sterol." Cholesterol is the animal sterol. Plants only make trace amounts of cholesterol, but make other sterols in larger amounts.

    The last region is the hydrocarbon tail. Like the steroid ring region, this region is composed of carbon and hydrogen atoms. Both the ring region and tail region are non-polar, which means they dissolve in fatty and oily substances but will not mix with water.

    Because cholesterol contains both a water-soluble region and a fat-soluble region, it is called amphipathic.

    What are HDL and LDL?

    "HDL" stands for "high-density lipoprotein." "LDL" stands for "low-density lipoprotein." Now the only question is, what’s a lipoprotein?

    Note that it is NOT cholesterol! It’s often said that HDL is the "good" cholesterol and LDL is the "bad" cholesterol as if there are two different kinds of cholesterol. There aren’t. The only kind of cholesterol that exists is pictured at the top of this page.

    Lipoproteins are carriers for cholesterol. If Bob’s car was in the shop (as usual) and he came to work with his wife’s newer, better car, would we say that the "good Bob" came to work today instead of the "bad Bob?" Like Bob’s car, lipoproteins are what cholesterol "get’s around" in.

    As the name suggests, the lipoproteins are part lipid (fatty substances), and part protein. Since proteins are soluble in water and lipids are mostly insoluble in water, the protein part of lipoproteins is used as an outside shell to transport the lipids contained within through the blood. (Blood is mostly water.) The outisde layer also includes phospholipids, which have water-soluble regions that also face the blood.

    The protein, then, is like the tires on Bob’s (or his wife’s) car, connecting the metal to the road. Since lipoproteins are immersed in the blood, rather than riding on top of it, they are spherical, ball-shaped, and the protein (and phospholipids) cover the entire outside of the ball.

    In addition to HDL and LDL, other lipoprotein carriers include chylomicrons, vLDL (very low-density), IDL (intermediate-density), and lipoprotein a.

    What’s the Difference Between HDL and LDL?

    HDLs differ from LDLs both in composition and function. HDLs consist of 40-55% protein, whereas LDLs consist of 20-25% protein. The rest of the lipoproteins are lipids, so LDLs are much richer in lipids than HDLs.

    HDL picks up cholesterol from most tissues and carries it to the liver for recycling or elimination or to cells that make steroid hormones. Cholesterol ester transfer protein can also allow HDL to drop cholesterol off into LDL particles. LDL carries cholesterol to most of the rest of the body for delivery to tissues.

  • I’m no expert but I have read some on the subject. From what I have discovered, the plaque that builds up in the arteries is composed of fatty material and is bound together by calcium.

  • Brandee

    Check out the link below:

  • aceofspd

    Cholesterol is a vital waxy like substance that is present in every cell of your body. It is necessary for many brain functions and is a precursor to the body’s sex hormones. It is a fat soluble substance so it CAN NOT travel in the blood. To do that, it needs to be combined with lipo proteins LDL, HDL, VLDL to travel where it is needed. Please note that the cholesterol that you eat, has nothing to do with the cholesterol, HDL and LDL that your doctor test for. Cholesterol is so vital to life that your body NEVER eliminates it. It is always recycled.
    Pharmacist who’s life was almost ruined by Lipitor


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