Lipid Metabolism 3yj57

The most of lipids in food are fat, so the metabolism of subject that we will discuss here is about FAT METABOLISM

Path of Fat Digestion

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Fat digestion particularly occurs in intestines, because inside mouth and stomach, lipase enzyme is not exist

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Solubility is the key issue in the digestion and absorption. Lipids are hydrophobic, and thus are poorly soluble in the aqueous environment of the digestive tract. Digestion is greatly aided by emulsification  the breaking up of fat globules into much smaller emulsion droplets. Bile salts and phospholipids are amphipathic molecules that are present in the bile. The emulsion droplets are where digestion occurs. Emulsification greatly increases the surface area where water-soluble lipase can work to digest triacylglycerol.

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Glyserols Fatty acids (70 %) Monoglycerides (20 %) Diglyserides The rest of trigyserides

After digestion, monoglycerides and fatty acids associate with bile salts and phopholipids to form micelles.  Micelles are much smaller than emulsion droplets.  Micelles are necessary because they transport the poorly soluble monoglycerides and fatty acids to the surface of the enterocyte where they can be absorbed. As well, micelles contain fat soluble vitamins and cholesterol. 

Once inside the enterocyte, monoglycerides and fatty acids are re-synthesized into triacylglycerold (TAG).  The TAG is packaged, along with cholesterol and fat soluble vitamins, into chylomicrons.  Chylomicrons are lipoproteins, special particles that are designed for the transport of lipids in the circulation. 

• Chylomicrons deliver absorbed TAG to the body's cells. • TAG in chylomicrons and other lipoproteins is hydrolyzed by lipoprotein lipase, an enzyme that is found in capillary endothelial cells. • Monoglycerides and fatty acids released from digestion of TAG then diffuse into cells.

Outer Shell is consist of polar protein (apoproteins) & phospholipid  Centre region contains triglycerides and ester cholesterols 

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Kilomikron  2% protein  Dihasilkan di dalam sel epitel usus dari lemak makanan  Untuk transport lipid dari hasil pencernaan dan absorbsi VLDL (Very Low Density Lipoprotein)  10% protein  Dihasilkan di hati terutama dari karbohidrat makanan  Mengangkut triasilgliserol yang dibentuk di hati ke dalam sel darah LDL (Low Density Lipoprotein)  25% protein (kolesterol jahat)  Dihasilkan di dalam darah  Mengandung kolesterol dan ester kolesterol dalam konsentrasi tinggi  Mengalami endositosis oleh hati dan jaringan perifer  Membawa 75% kolesterol darah ke sel tubuh HDL (High Density Lipoprotein)  40% protein (kolesterol baik)  Dihasilkan di hati dan usus  Mempertukarkan protein dan lemak dengan lipoprotein lain  Mengembalikan kolesterol dari sel ke hati untuk dieliminasi

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1 triglyceride has 48 atom C  form 24 acetyl  Each acetyl undergoes 1 turning of Creb cycle  Each Creb Cycle yields 3 NADH, 1 FADH, 1 ATP.

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So, 24 turning of Creb Cycles yield :  72 NADH  24 FADH  24 ATP

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How much of ATP yielded from triglyceride ?

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72 NADH x 3 = 216 ATP 24 FADH x 2 = 48 ATP 24 ATP directly= 24 ATP

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ATP : 288 ATP

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Glycolysis = 2 ATP, 2 NADH O.D. = 2 NADH 2 Acetyl, 2 turn of Creb cycles yields siklus Kreb 6 NADH, 2 FADH, 2 ATP

 Total ATP = 38 ATP

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Lipid yields more ATP than carbohydrate but needs longer time for the catabolism.

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Carbohydrates yields less ATP but the catabolism is fast.

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Conclusion ? It depends on….

LIPOLYSIS

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A fatty acid reacts with ATP and coenzyme A to form acyl CoA, AMP and pyrophosphate.

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This reaction is catalysed by acyl CoA synthetase.

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The formations of malonyl coenzyme A is the speed determining step in the fatty acid synthesis.