Biokimia pencernaan lemak

lipid

Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform, benzene, acetone).Lipids include fats, oils, waxes and related compounds.

CLASSES of LIPIDSSIMPLE LIPIDS• Fat• Oil • Waxes

COMPLEX LIPIDS• Phospholipids• Glycolipid

DERIVED LIPIDS• Fatty acid• Sterol

Lipids

Lipids: family of biochemicals that are soluble in organic solvents but not in waterClasses:

Waxes: fatty acid + a long-chain alcoholTriglycerides (fats & oils): glycerol + 3 fatty acids Phospholipids: glycerol + 2 fatty acids + phosphate + amino alcoholGlycolipids: glycerol or spingosine + fatty acid + monosaccharideSteroids: 3 cyclohexanes + 1 cyclopentane fused together

Fatty Acids

Fatty acids: long-chain carboxylic acidsForm fats and oils (usually have an even number of carbons)Saturated fatty acid: all single bondsUnsaturated fatty acid: at least 1 double bond

Polyunsaturated: two or more double bondsMost double bonds are cis- bonds that cause a bend in the chain

Fatty Acids

FATTY ACIDS

SATURATION• SATURATED FATTY ACID =If all

the carbon atoms in the chain are joined with single bonds, and the remaining bonds are attached to hydrogen

FATTY ACIDS

• UNSATURATED FATTY ACID = If adjoining carbons are joined by double bonds

FATTY ACIDS

UNSATURATED• One double bond =

monounsaturated fatty acid• Two or more double bonds = poly- unsaturated fatty acid

Fats and Oils

Fats: more saturated fatty acids; solid at room temperatureOils: more unsaturated fatty acids; liquid at room temperature

Omega 3

Omega 6

Omega 9

FATTY ACIDS• Nonessential Fatty Acids – our body

can make certain fatty acids so they are not required in the diet

• Essential Fatty Acids – our bodies cannot make C-C double bonds before the 9th carbon from the methyl end, so we must get these fatty acids from our diet

• EFAS = omega-6 linoleic acid & omega-3 alpha-linolenic acid

FATTY ACIDS

• Omega-3: Alpha-Linolenic Acid (ALA), Eicosapentaenoic Acid (EPA), Docosahexaenoic Acid (DHA)

• Omega-6: Linoleic Acid, Arachidonic Acid

Phospholipids

Phospholipid:alcohol + phosphate +fatty acid

Glycerophospholid: glycerol + 2 fatty acids + phosphate/amino alcohol

Lecithins and cephalins abundant in brain & nerve tissue, egg yolks, wheat germ, and yeastForms cell membranes

Phospholipids

Sphingolipid: sphingosin + fatty acid + phosphate/amino alcohol

A phospholipid with sphingosin instead of the glycerolImportant in the myelin sheath that surrounds most nerve fibers

Glycolipid: glycerol + 1 fatty acid + sugar

In cell membranes Function in cell adhesion & self-identity markers

Phospholipids in Foods

• A typical diet contains only about 2 grams per day

• Lecithin (phosphatidylcholine) is the major phospholipid and is found in:

Liver, egg yolk, soybeans, peanuts, legumes, spinach, and wheat germ

• Usually lost during food processing

TRIGLYCERIDES

STRUCTURE• Triglyceride - three fatty acids

attached to a glycerol backbone • Diglyceride – two fatty acids

+glycerol• Monoglyceride – one fatty acid

+glycerol

TriglycerideFatty Acids

A Lipoprotein

Chylomicrons are lipoproteins

Reverse Cholesterol Transport via HDLBloodBloodPeripheralTissuesPeripheralTissues

LiverLiver

Bile

ExcessCholesterol

β oksidasisetelah memasuki sel FA masuk ke matriks mitokondria degradasi lebih lanjut.

FA diaktivasi dgn ensim fatty acyl – CoA ligase atau Acyl CoA synthase / thiokinase

Ensim ini spesifik utk tiap jenis asam lemak

Untuk masuk ke dalam matrik mitokondria, asam lemak yg sudah diaktivasi memerlukan karier karnitin

- Karnitin asiltransferase I : membran luar

- Karnitin asiltransferase II : membran dalam

Step 1 : dehidrogenasi / oksidasi

• Berperan pada pembentukan rantai ganda antara atom C2 – C3.

• Mempunyai akseptor hidrogen FAD+.

• Antara asam lemak yg berbeda panjangnya beda enzimnya,

Step2 : Hidratasi• Mengkatalisis hidrasi trans

enoyl CoA

• Penambahan gugus hidroksi pada C no. 3

• Ensim bersifat stereospesifik

• Menghasilkan 3-L-hidroksiasil Co. A

Step 3 : dehidrogenasi

• Mengkatalisis oksidasi -OH pada C no. 3 / C β menjadi keton

• Akseptor elektronnya : NAD+

Step 4 : thiolisis

• β-Ketothiolase mengkatalisis pemecahan ikatan thioester.

• Acetyl-CoA dilepas dan tersisa asam lemak asil ko A yang terhubung dgn thio sistein mll ikatan tioester.

• Tiol HSCoA menggantikan cysteine thiol, menghasilkan fatty acyl-CoA (yang telah berkurang 2 C).