Cholesterol Metabolism

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L21

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5 Terms

1
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What are lipoproteins? what’s the structure?

  • transports TAG produced in liver into bloodstream

  • center: transport molecule carrying TAGs & Cholesterol esters

  • outside: thin monolayer of phospholipids & cholesterol

  • surface: apoproteins

<ul><li><p>transports TAG produced in liver into bloodstream</p></li><li><p><strong>center</strong>: transport molecule carrying <strong>TAGs &amp; Cholesterol esters</strong> </p></li><li><p><strong>outside</strong>: thin monolayer of <strong>phospholipids &amp; cholesterol</strong></p></li><li><p><strong>surface</strong>: <strong>apoproteins</strong></p></li></ul><p></p>
2
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what are cholesterol made from? what does it require? How is it regulated?

  • from acetyl-CoA using C from fat/protein/carbohydrate metabolism

  • requires NADPH & ATP

  • regulated by inhibiting HMB-CoA reductase via phosporylation / statins

3
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what are the 3 types of lipoproteins?

  1. Chylomicrons

    • made in small intestine

    • largest

    • contain most TAGs

  2. VLDL

    • sent by liver

    • distribute TAGs & cholesterol

    • binds lipoprotein lipase → hydrolyze & release TAGs

      • producing Intermediate Density Protein (IDL) → Low Density Protein (LDL) “bad cholesterol”

  3. HDL

    1. “good cholesterol”

    2. contains LCAT enzyme → picks up cholesterol for transport back to liver (break down & recycling)

<ol><li><p><strong>Chylomicrons</strong></p><ul><li><p>made in small intestine</p></li><li><p>largest</p></li><li><p>contain most TAGs</p></li></ul></li><li><p><strong>VLDL</strong></p><ul><li><p>sent by liver</p></li><li><p>distribute TAGs &amp; cholesterol</p></li><li><p>binds <strong>lipoprotein lipase</strong> → hydrolyze &amp; <strong>release TAGs</strong></p><ul><li><p>producing Intermediate Density Protein (IDL) → <strong>Low Density Protein</strong> (LDL) <u>“bad cholesterol”</u></p></li></ul></li></ul></li><li><p><strong>HDL</strong></p><ol><li><p><u>“good cholesterol”</u></p></li><li><p>contains <strong>LCAT enzyme </strong>→ <strong>picks up cholestero</strong>l for transport back to liver (break down &amp; recycling)</p></li></ol></li></ol><p></p>
4
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What is lipoprotein’s mechanism in circulation?

  • lipoprotein lipase (LPL) is located on capillary wall

  • bound by apoproteins (non-covalent)

  • LPL hydrolyzes TAGs into FFA & glycerol

<ul><li><p><strong>lipoprotein lipase</strong> (LPL) is located on <strong>capillary wall</strong></p></li><li><p>bound by <strong>apoproteins</strong> (non-covalent)</p></li><li><p>LPL <u>hydrolyzes</u> TAGs into FFA &amp; glycerol</p></li></ul><p></p>
5
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what is the biochemical logic behind how exercise can lead to inhibition of fat synthesis via kinases?

  • exercise leads to:

    • ⬆epinephrine → phosphorylation

    • ⬆AMP (due to ATP hydrolysis) → activates AMP Kinase → phosphorylates ACC = ⬇malonyl-CoA = ⬆CATI activity = ⬆beta-oxidation = ⬆fat degradation = ⬇fat synthesis