1. 13.9 What Are Steroids Kristin Miller Caleb Conrad

2. Steroids • 3rd major class of lipids • Contains the following ring system:

3. Cholesterol • The most abundant steroid in the human body • Purpose • Plasma membrane component • Red blood cells • Raw material for synthesis of other steroids • Sex, adrenocorticoid hormones and bile salts • Exists free form and esterified fatty acids • Gall stones contain free cholesterol • Many think it’s a bad thing • Correlation with high serum cholesterol levels • Necessary to human life • Liver manufactures enough for our daily needs

4. Constantly circulates in blood • It’s hydrophobic • Needs water soluble carrier to circulate in aqueous medium of blood

5. Lipoproteins: Carriers of cholesterol • Contain core of hydrophobic lipid molecules surrounded by a shell of hydrophobic molecules • Four kinds of lipid proteins • High- density (“good cholesterol”) • 33% protein 30% cholesterol • Low- density (“bad cholesterol”) • 25% protein 50% cholesterol • Very-low-density • Comes from triglycerides synthesized by the liver • Chylomicrons • Carry dietary lipids synthesized in intestines

6. Transport of cholesterol • To liver • Starts as large VLDL particles (55 nanometers in diameter) • Core contains triglycerides and cholesteryl esters • Surrounded by polar coat phospholipids and proteins • Reaches muscle or fat tissue • Triglycerides and proteins are removed from VLDL (aPOB-100 isn’t) • Lipoprotein shrinks 22 nanometers • Contains only cholesteryl esters • Fat is removed, becomes more dense, turns into LDL • LDL Stays in plasma for about 2.5 days

7. LDL • Carries cholesterol to cells • Concentrated areas called coated pits • aPOB- 100 protein • Binds to LDL receptor molecules • LDL taken inside of cell • Enzymes break down into lipoproteins • During the process • Free cholesterol liberated from cholesteryl esters • Cell can then tell if it’s a component of a membrane • No enough LDL receptors? • Cholesterol accumulates in blood

8. Transport of cholesterol in HDL • Cholesterol from peripheral tissues to liver • Transfer cholesterol to LDL • In serum, free cholesterol in HDL convert to cholestryl esters • Delivered to liver for synthesis of bile, acids, and steroid hormones • Does not involve endocytosis & degradation of lipoproteins • Selective lipid uptake • HCL binds to liver cell surface & transfers cholestryl ester to cell • HDL depleted from lipid content • Reenters circulation • Bodies with high HDL • Remove cholesterol from blood stream

9. Levels of LDL and HDL • Cholesterol = insoluble in water • If elevated in blood stream • Plaque deposits form in arteries • Decreases blood flow • Leads to high blood pressure which leads to • Heart attack, stroke, kidney failure • Clot arteries = less oxygen • Mayocardio infraction

10. Most cholesterol is transferred by LDL’s • A lot of LDL receptors = cholesteroleasily removed from body • Synthesis of LDL’s goes up, LDL receptors are surpressed • Causes LDL concentration in plasma to rise • Not enough LDL receptors • Familial hypercholesterolemia • Plasma is 680 mg/100 mL compared to 175 mg/100 mL • Can cause atherosclerosis and heart attack • High LDL = low HDL • Results in atherosclerosis

11. High serum cholesterol • Synthesis is low • Synthesis inhibitors • Diets low in cholesterol and saturated fatty acids • Prescription drugs • Zocor, Lipitor, • Block biocatalysts in cholesterol synthesis • What do you want in your body? • High HDL • Carry plaque out of arteries to liver • Increased with exercise and weight loss • Low LDL