LEMAK : STRUKTUR, FUNGSI DAN METABOLISME

Artharini I

LEMAK ???

kolesterol

Obesitas

diabetes

Hipertensi

Jantung

Health issues

Excessive dietary fat intake is associated with obesity, diabetes, cancer, hypertension and atherosclerosis.

Not more than 35% of energy intake should come from fat. Saturated fat should not make up more than 15% of the total fat intake.

Omega-3 fatty acids (20 carbons) from fish may protect against atherosclerosis. American Heart association recommends 2-3 fish meals per weak. Fish oil supplements should be avoided because they may be contain concentrated toxins accumulated by the fish.  

DEFINISI LEMAK

Senyawa yang larut dalam pelarut lemak, seperti kloroform, benzena, hexan, aseton dan eter.

Ester asam lemak dan gliserol (trigliserida)

Bentuk padat : lemak cair : minyakKenapa energinya lebih tinggi?

Kandungan C, H dan O

C H O

Lemak 77 12 11

Pati 44 6 50

FUNGSI:

Komponen struktural membran selSebagai sumber energi, umumnya dalam

bentuk trigliseridaPelarut vitamin yg larut pada lemakSebagai prekursor biosintetik ( hormon

steroid dari kolesterol)Untuk memproteksi (contoh melapisi

ginjal)Untuk insulasi panas

SIFAT UMUM LEMAK

Relatif tidak larut dalam airLarut dalam pelarut non polar (eter,

kloroform)Merupakan konstituen makanan yg penting

( energinya lebih tinggi, adanya vitamin larut dlm lemak, asam lemak essensial)

Disimpan di jaringan adiposa insulator panas

Kombinasi lipid dengan protein alat pengangkut lipid dlm darah

KLASIFIKASI LEMAK (Harper)

1. LIPID SEDERHANAEster asam lemak dengan berbagai alkohol- Lemak (fat) : ester as. Lemak dengan gliserol; minyak (oil) lemak dlm kondisi cair- wax (malam) : ester asam lemak dg alkohol monohidrat berberat molekul tinggi

2. LIPID KOMPLEKSEster asam lemak yg mgd gugus2 selain alkohol dan asam lemak- Fosofolipid- Glikolipid- lipid kompleks lain (sulfolipid, aminolipid)

3. PREKURSOR DAN LIPID TURUNAN-asam lemak, gliserol, steroid, alkohol lain, aldehid lemak,badan keton, hidrokarbon, vitamin larut lemak dan hormon.

Bloor’s ClassificationA. Simple lipid - ester of fatty acids with various alcohols

1. Natural fats and oils (triglycerides)

2. Waxes

(a) True waxes: cetyl alcohol esters of fatty acids

(b) Cholesterol esters

(c) Vitamin A esters

(d) Vitamin D esters

B. Compound lipid - esters of fatty acids with alcohol plus other groups

1. Phospholipids and spingomyelin: contains phosphoric acid and often a nitrogenous base

2. Spingolipids (also include glycolipids and cerebrosides): contains aminoalcohol spingosine, carbohydrate, N-base; glycolipids contains no phosphate

3. Sulfolipids : contains sulfate group

4. Lipoproteins : lipids attached to plasma/other proteins

5. Lipopolysaccharides: lipids attached to polysaccharides

Classification

CH3

OH

CH3

CH3

CH3 CH3

E E E E

C. Derived lipids – hydrolytic products of A & B with lipid characters

1. Saturated & unsaturated fatty acids

2. Monoglycerides and diglycerides

3. Alcohols (b-carotenoid ring, e.g., vitamin A, certain carotenoids)

D. Miscellaneous lipids

1. Aliphatic hydrocarbons: found in liver fat and certain hydrocarbon found in beeswax and plant waxes

2. Carotenoids

3. Squalene : found in shark and mammalian liver and in human sebam; an important intermediate in

biosynthesis of cholesterol

4. Vitamin E and K

Classification cont.

REAKSI PEMBENTUKAN LEMAK

CH2OH HOOC-R CH2-OOC-R

CHOH + HOOC-R --- CH-OOC-R + 3H2O

CH2OH HOOC-R CH2-OOC-R

Gliserol asam lemak lemakair

NOMENCLATURE AND STRUCTURE

Fats and oils: Vegetable oils are triglycerides that are liquid at room

temp due to their higher unsaturated or shorter-chain fatty acids

Triglycerides are most abundant natural lipids

Natural fats have D-configurationUsually R1 and R3 are saturated and R2 is unsaturatedNatural fats are mixture of two or more simple

triglycerides

FATTY ACIDS

“ A fatty acid may be defined as an acid that occurs in a natural triglyceride and is a mono carboxylic acid ranging in chain length From four carbon to 24 carbon atoms and including , with

exceptions, only the even-numbered members of the series ”

SIFAT

Ditentukan o/ susunan as.lemaknya:

1. Jenuh/saturated (CnH2nO2)

2. Tidak jenuh/unsaturated (CnH2n-xO2) Punya 2 atau lebih molekul H yg

hilang Esensial bagi tubuh

Most Common Fatty Acids in Di- and Triglycerides

Fatty acid Carbon:Double bonds

Double bonds

Myristic 14:0

Palmitic 16:0

Palmitoleic 16:1 Cis-9

Stearic 18:0

Oleic 18:1 Cis-9

Linoleic 18:2 Cis-9,12

Linolenic 18:3 Cis-9,12,15

Arachidonic 20:4 Cis-5,8,11,14

Eicosapentaenoic 20:5 Cis-5,8,11,14,17

Docosahexaenoic 22:6 Cis-4,7,10,13,16,19

CH3(CH2)nCOOH

Sumber : Lehninger,

Sumber : Lehninger,

Sumber : Lehninger,

Fatty Acid Isomers

LIPID CONTENT OF FEEDS

ForagesFat content is low: 1 to 4% of dry matterHigh proportion of linolenic acid (18:3)Diglycerides in fats of leaves

GrainsFat content variable: 4 to 20% of dry matterHigh proportion of linoleic acid (18:2)Triglycerides in oils of seeds

Sumber : Lehninger,

REAKSI KIMIA & SIFAT KHAS LEMAK

1. HIDROLISIS

A. ENZIMATIK

trjd dlm pencernaan

B. DG ALKALI (PENYABUNAN)

Lipida+alkali gliserol

grm alkali

as.lemak

REAKSI KIMIA & SIFAT KHAS LEMAK2. ANALISIS

a. Bil.Penyabunan adalah jml mg KOH u/menyabunkan 1 gr lemak

b. Bil.As adalah jml mg KOH u/menetralkan as.lemak bebas dr 1 gr lemak

c. Bil.Polenske adalah jml mg KOH u/menetralkan as.lemak yg tdk larut (yg bukan atsiri dlm destilasi uap) dr 5 gr lemak

REAKSI KIMIA & SIFAT KHAS LEMAK

d. Bil.Iodium (ukuran derajat ketidakjenuhan)

- jml gr iodium yg diserap o/ 100 gr lemak (tiap ik.ganda dlm lemak dpt mengambil 2 atom iodium)

e. Uji ketengikan (ukuran derajat ketengikan)- Bil Peroksida (dg KI)- Uji As.Tiobarbiturat- Uji Oven Schaal

KETENGIKAN

1. HIDROLITIKa. Adanya lipase bs menyebabkan reaksi ini, terbentuk as.lemak+gliserolb. nilai gizi tdk terpengaruh

2. OKSIDATIFa. Trjd krn adanya oksigen b. menurunkan nilai energi dr lemak

METABOLISME LEMAK

Istilah2 terkait dengan Metab. Lemak

Lipogenesis Beta Oksidasi

Lipid Metabolism

MEMBRAN LIPIDS

Glycerophospholipid Galactolipid Sulfolipid Sphingolipid sterol

Glycerophospholipids

Glycerophospholipids (phosphoglycerides), are common constituents of cellular membranes.They have a glycerol backbone.Hydroxyls at C1 & C2 are esterified to fatty acids.

C OHH

CH2OH

CH2OH

glycerol

An ester forms when a hydroxyl reacts with a carboxylic acid, with loss of H2O.

Formation of an ester:

O O

R'OH + HO-C-R" R'-O-C-R'' + H2O

Phospholipids• Phospholipids consist

of a 3-carbon glycerol linked to a negatively charged phosphate group, and two fatty acids.

• Phospholipids are a major component of cell membranes due to their amphipathic nature.

• Amphipathic molecules have a nonpolar region (hydrophobic) and a polar region (hydrophilic).

41

Sphingosine may be reversibly phosphorylated to produce the signal molecule sphingosine-1-phosphate. Other derivatives of sphingosine are commonly found as constituents of biological membranes.

H2CHC

OH

CH

N+ CH

C

CH2

CH3

H

H3

OH

( )12

sphingosine

Sphingolipids are derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group.

sphingosine-1-P

H2CHC

O

CH

N+ CH

C

CH2

CH3

H

H3

OH

( )12

P O

O

O

Sphingomyelin, with a phosphocholine head group, is similar in size and shape to the glycerophospholipid phosphatidyl choline.

Sphingomyelin has a phosphocholine or phosphethanolamine head group.

Sphingomyelins are common constituent of plasma membranes

H2CHC

O

CH

NH CH

C

CH2

CH3

H

OH

( )12

C

R

O

PO O

O

H2C

H2CN+

CH3

H3C

CH3

Sphingomyelin

phosphocholine

sphingosine

fatty acid

-oxidation yields large amounts of ATP

The energy conversion process of fatty acid --> ATP involves oxidation of fatty acids by sequential degradation of C2 units leading to the generation FADH2, NADH, and acetyl CoA.

The subsequent oxidation of these reaction products by the citrate cycle and oxidative phosphorylation generates lots of ATP.

Palmitate(C16)

106 ATP - WOW!

-oxidation reactions

The -oxidation pathway occurs at the carbon of the fatty acid, thereby releasing the C-1 carboxyl carbon and carbon as the acetate component of acetyl CoA.

OXIDATION

HYDRATION

OXIDATION

THIOLYSIS

-oxidation reactions for palmitate (C16)

Palmitoyl-CoA + 7 CoA + 7 FAD + 7 NAD+ + 7 H2O -->

8 acetyl CoA + 7 FADH2 + 7 NADH + 7 H+

31 NADH (31 x ~2.5 ATP) = ~77.5 ATP15 FADH2 (15 x ~1.5 ATP) = ~22.5 ATP

For a grand total = 100 ATP

After subtracting the 2 ATP required for fatty acyl CoA activation (AMP --> PPi)

And adding the 8 ATP obtained from eight turns of the citrate cycle;

The total payout for the complete oxidation of palmitate is 106 ATP

ATP currency exchange ratios

-oxidation is a chemical source of water for desert animals

Besides the payout of ATP that comes from fatty acid oxidation, another benefit is the generation of H2O that occurs when O2 is reduced by the final reaction in the electron transport system, as well as, the formation of H2O in oxidative phosphorylation.

2 NADH + 2 H+ + O2 --> 2 H2O 2 FADH2 + O2 --> 2 H2O ADP + PO4

2- --> ATP + H2O

KetogenesisWhen fatty acid oxidation produces more acetyl-CoA than can be combined with OAA to form citrate, then the "extra" acetyl-CoA is converted to acetoacetyl-CoA and ketone bodies, including acetone. Ketogenesis (synthesis of ketone bodies) takes place primarily in the liver.

KetogenesisAcetyl-CoA derived from fatty acid oxidation enters the Citrate Cycle only if carbohydrate metabolism is properly balanced.

When fatty acid oxidation produces more acetyl-CoA than can be combined with OAA to form citrate, then the "extra" acetyl-CoA is converted to acetoacetyl-CoA and ketone bodies, including acetone. Ketogenesis (synthesis of ketone bodies) takes place primarily in the liver.

Ketones are an energy source for tissues

Ok, now what happens to these two acetyl-CoA?

How many total ATP from 2 acetyl-CoA?

6 NADH2 FADH22 GTP

15 ATP3 ATP2 ATP

20 ATP

Ketogenesis occurs when glycogen stores are depleted such as during fasting and in undiagnosed diabetics

Diabetics can have high levels of acetone in their blood which can be detected on their breath as a fruity odor. Acetone is a spontaneous breakdown product of acetoacetate (decarboxylation), or it is formed by enzymatic cleavage of acetoacetate by the enzyme acetoacetate decarboxylase.

Lipoprotein and lipid transport

• Since cholesterol is hydrophobic (water fearing) and blood is hydrophilic (water loving), the two do not mix.

• Cholesterol is carried through the bloodstream in protein packages called lipoproteins, made up of lipid on the inside and protein on the outside.

• Two kinds of lipoproteins carry cholesterol throughout your body.

58

- High density lipoproteins (HDL) - Low density lipoproteins (LDL)

LDL and HDL continued….

• LDL cholesterol is sometimes called bad cholesterol. – High LDL cholesterol leads to a buildup of cholesterol in

arteries. The higher the LDL level in your blood, the greater chance you have of getting heart disease.

• HDL cholesterol is sometimes called good cholesterol. – HDL carries cholesterol from other parts of your body back

to your liver. The liver removes the cholesterol from your body. The higher your HDL cholesterol level, the lower your chance of getting heart disease.

59

Hyperlipidemia can lead to disease• When there is too much

cholesterol /LDL in your body (because of diet and the rate at which the cholesterol is processed) it is deposited in arteries, including those of the heart, which can lead to narrowing of the arteries and heart disease.

• Studies of people with heart disease have shown that lowering cholesterol/LDL reduces the risk for dying from heart disease, having a heart attack, or needing heart bypass surgery or angioplasty.

60

Lipoprotein Profile

• Cholesterol levels are measured in milligrams (mg) of cholesterol per deciliter (dL) of blood.

• Desirable or optimal levels for adults with or without existing heart disease are: – Total cholesterol: Less than 200 mg/dL. – Low Density Lipoprotein (LDL) cholesterol: Less than 100 mg/dL. – High Density Lipoprotein (HDL): 40 mg/dL or higher. – Triglycerides: Less than 150 mg/dL.

• The National Cholesterol Education Program recommends that healthy adults over 20 years of age have their cholesterol levels checked once every 5 years.

61