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47 Cards in this Set
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- Back
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What are the functions of cholesterol?
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-Inserts in membranes
-Precursor of bile salts -Precursor of steroids -Precursor of vitamin D |
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Where does the bulk of De Novo cholesterol synthesis occur?
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LIVER
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How is cholesterol leaving the liver?
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-Component of HDL's
-Component of VLDL's -Free Cholesterol as bile salts and acids |
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Where do the carbons used for cholesterol synthesis arise?
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Acetate, NADPH supplies e-'s
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Where does cholesterol synthesis occur in the hepatocyte?
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Cytosol and endoplasmic reticulum
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Cholesterol synthesis starts the exact same way that ketone synthesis does with the exception of what?
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It is occuring in the cytosol of the cell and not the matrix. (2) AcCoA are combined to form Acetoacetyl CoA and then HMG-CoA but in the cytosol. By the enzymes Thiolase, and HMG CoA synthase.
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What is the product of HMG-CoA via the enzyme HMG-CoA reductase in cholesterol synthesis?
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Hydroxymethyglutaryl CoA ("HMG-CoA")
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What is important about the enzyme HMG-CoA reductase?
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It is the rate limiting enzyme for cholesterol synthesis and is only found in the liver.
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What inhibits the rate limiting enzyme HMG-CoA reductase?
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Cholesterol
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Whats important to note about the steps from Mevalonic acid in cholesterol synthesis to squalene?
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There are many steps, intermediates are phosphorylated, ATP is used to the tune of 7 ~P's, and 1 NADH is consumed (worth 3 ATP)
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How many NADPH's are used in the conversion of HMG-CoA to Mevalonic acid via HMG-CoA reductase?
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2 NADPH are used, and (1) CoA is released
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What is notable about the conversion of Squalene, a cholesterol synthesis intermediate, to Lanosterol?
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(1) O2 and (1) NADPH are required, yielding (1) NADP and (1) H2O. Also, the structures from this point on are very hydrophobic and are bound to a carrier protein
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What is the immediate precursor to cholesterol?
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Lanosterol, there are no remarkable steps Tim would like us to know about this step.
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What are Lovastatin & Metastatin?
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Anti-Cholesterol (hypolipidemic) drugs that inhibit HMG-CoA reductase (the rate limiting enzyme of cholesterol synthesis)
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Can cholesterol be used for energy? And what is its fate?
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No, it cannot.
It is used in bile acids, which can be excreted in the feces, or free cholesterol in bile that remains in the feces. -Also, cholesterol can be used to make steroid hormones. |
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How many classes of steroid hormones are there and what are they?
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There are 5:
-Glucocorticoids (Cortisol) -Mineralcorticoids (Aldosterone) -Androgens (Testosterone) -Estrogens (Estradiol) -Progestins (Progesterone) |
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What determines the specific hormone a tissue produces?
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What enzyme it contains, based on gene expression
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Do both hormones and steroid hormones circulate in the blood freely?
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Hormones circulate freely in the blood,
Steroid hormones are hydrophobic and are transported in the blood bound to: Albumin, Transcortin (in case of cortisol), and Sex Hormone Binding Protein for the sex hormones. |
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What is the rate limiting enzyme for steroid hormone synthesis?
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Desmolase
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What is desmolase?
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It is the rate limiting enzyme for synthesis of all hormones
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What is the function of desmolase?
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Converts cholesterol to pregnenolone using (1) NADPH and (1) O2.
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What are the many fates of Pregnenolone?
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Corticosterone->Aldosterone
Progesterone--->Cortisol Testosterone--->Estradiol |
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Can steroids be stored?
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No, steroids are lipid soluble so they would pass through lipid membranes. They are made on-demand and automatically leave endocrine cells.
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What is the "Demand" that is a regulatory polypeptide hormone responsible for stimulating desmolase activity in the endocrine cell?
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ACTH in the example he gave us, binds the receptor stimulating a 2nd messenger which stimulates Desmolase activity which enzyme converts cholesterol to pregnenolone
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How do steroids alter cell behavior?
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The alter cell gene expression
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What is the total activity of a protein?
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Its specific activity multiplied by the amount or # or enzyme molecules
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In addition to becoming steroids, what else can FA's become?
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Intercellular signals called Eicosanoids (which contain 20 carbons)
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What are eicosanoids?
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20 carbon unit molecules derived from FA's:
-Prostaglandins -Thromboxanes -Leukotrienes |
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Why aren't Eicosanoids hormones?
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They have a short life-expectancy and almost no time to circulate in blood to effect distant tissues/cells.
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What are Eicosanoids also known as?
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Paracrines. Compounds which aren't steroids or hormones but alter the behavior of neighboring cells. Paracrines are very potents and produced varied responses throughout the body.
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What is an example of an eicosanoid?
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Arachidonic acid
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What is the precursor of arachidonic acid?
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Linoleic acid, an essential FA. We also get dietary arachidonic acid.
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What is the source of arachidonate for prostaglandin synthesis?
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Phospholipids present in our diet.
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Phospholipid in cell membranes is converted to arachidonic acid via which process?
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Phospholipase A2 cleaves phospholipids yielding Arachidonic acid and a lysophospholipid
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What inhibits the activity of Phospholipase A2?
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Corticosteroids (cortisol, cortisone)
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What is the fate of arachidonic acid?
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Converted to 5-HPETE via 5-lipoxygenase
Converted to Prostaglandin G2 (PGG2) via cyclo-oxygenase found in microsomes |
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What is the fate of 5-HPETE from Arachidonic acid?
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Becomes Leukotriene A4 and other Leukotrienes
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What is the fate of Prostaglandin G2 (PGG2)?
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Converted via peroxidase to PGH2, which can then become:
Thromboxane A2 via thromboxane synth. PGI2 (prostacyclin) PGE2--->PGF2alpha |
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What are leukotrienes?
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Factors that respond to tissue damage.
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What is the action of leukotrienes?
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Smooth muscle contract
Bronchoconstriction Slow anaphalaxis Lysosomal release White BC adhesion |
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What is Thromboxane A2 and its effects?
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Mostly made by platelets and promote aggregation and vasoconstriction at wound sites.
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What is PGE2 and its function?
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Most tissues synthesize it but especially the kidney, causes vasodilation and is also used to promote labor.
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What is PGF2 and its function?
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Made in most tissues. A vasoconstrictor which stimulates smooth muscle and uterine contraction.
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What is PGI2 and its function?
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Prostacyclin; Primarily made by endothelial cells and causes vasodilation and inhibits platelet aggregation.
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Are cyclo-oxygenase and peroxidase two separate enzymes?
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No, they are two domains of the same protein complex called prostaglandin synthase
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What inhibits cyclo-oxygenase activity?
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Aspirin, other NSAIDS, Indomethacin, phenylbutazone. These factors provide their anti-inflammatory effects via this mechanism.
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What does Dipyridamole do?
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Inhibits Thromboxane synthase, inhibiting thromboxane production without affecting PG's (prostaglandins)
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