Lipid Metabolismdr. Hesty WahyuningsihDept. Biokimia

Out lineOverview of Human MetabolismLipids of Physiologic SignificanceLipid metabolism: DegradationDigestionAbsorption Lipid transport -oxidationBiosynthesis

Overview of Human MetabolismHarpers Illustrated Biochemistry

Harpers Illustrated Biochemistry

LIPID

: hydrocarbon, hydrophobic.

Consist of:triacylgycerol, phopholipid, cholesterol

LIPID METABOLISMDegradationDigestionAbsorption Lipid transport -oxidation

Biosynthesis fatty acid synthesis cholesterol synthesis

DIGESTION, ABSORPTION and TRANSPORT of LIPID Bile salts help in the digestion of fats, cholesterol and fat-soluble vitamins by forming mixed micelles which solubilize the fats and render them accessible to digestive enzymes. The presence of free fatty acids in the duodenum causes release of the peptide hormone cholecystokinin which causes the gallbladder to release bile salts and the pancreas to release pancreatic lipase. Pancreatic lipase hydrolyzes triglycerides (triacylglycerols) to give free fatty acids and 2-monoglycerides which are absorbed by the intestinal mucosa cells. Short-chain fatty acids (< C12) enter the portal vein and are transported directly to the liver.

All other fatty acids are re-esterified with the 2-monoglycerides to form triglycerides which are incorporated into lipoprotein particles called chylomicrons which enter the lymphatic vessels.

Harpers Illustrated Biochemistry

Lipoprotein1. Chylomicron: transport lipid which form from digesting and absorbing (>Triasilgliserol)2. VLDL: transport triacilgliserol from liver (>Triasilgliserol)3. LDL : rich of cholesterol, forming from VLDL metabolism4. HDL : rich of cholesterol at joint cholesterol secretion process from the tissue (> Protein)

3 jalur metabolisme lipoprotein

Metabolisme EksogenMetabolisme EndogenReverse Cholestrol Transport

Harpers Illustrated Biochemistry

exogneHarpers Illustrated Biochemistry*FAT TISSUES

endogneHarpers Illustrated Biochemistry*FAT TISSUES

REVERSE COLESTROL TRANSPORTHarpers Illustrated Biochemistry

Figure 24.13

EnergyLipidProtineGlycogneGlucose40 kcal600 kcal25.000 kcal100.000 kcal

- Oksidasisetelah memasuki sel asam lemak masuk ke matriks mitokondria degradasi lebih lanjut.

Step 1. Asam lemak diaktivasi dgn enzim Acyl CoA synthase / thiokinase

Harpers Illustrated Biochemistry

Untuk masuk ke dalam matrik mitokondria, asam lemak yg sudah diaktivasi memerlukan karier karnitinKarnitin palmitoiltransferase I : membran luarKarnitin palmitoiltransferase II : membran dalam

Harpers Illustrated Biochemistry

Harpers Illustrated Biochemistry

Setelah di dalam mitokondria.....

STEP 2:Berperan pada pembentukan rantai ganda antara atom C2 C3. Mempunyai akseptor hidrogen FAD+.

STEP 3:Mengkatalisis hidrasi trans enoyl CoAPenambahan gugus hidroksi pada C no. 3Menghasilkan 3-L-hidroksiasil Co. A

Harpers Illustrated Biochemistry

STEP 4:Mengkatalisis oksidasi -OH pada C no. 3 / C menjadi keton Akseptor elektronnya : NAD+TEP

STEP 5 :Thiolase mengkatalisis pemecahan ikatan thioester. Acetyl-CoA dilepas dan tersisa asil ko A menghasilkan fatty acyl-CoA (yang telah berkurang 2 C).

Harpers Illustrated Biochemistry

Lipogenesis and LipolysisFigure 24.14

HSL: hormone sensitive lipase, TG: trigliserid, FFA: Free fatty acid, FA: fatty acid, AcCoA: acetyl Co-A

****Ini alasan mengapa lemak menghasilkan energi yang sangat besar jika dibandingkan karbohidrat dan protein. Dalam 1 rantai asam lemak dg 16 C bisa menghasilkan 8 asetil KoA, padahal dalam 1 gugus triasil gliserol ada 3 untai asam lemak.***