Artharini I
LEMAK : STRUKTUR, FUNGSI
DAN METABOLISME
LEMAK ???
kolesterol
Obesitas
Hipertensi
diabetes
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 : minyak
Kenapa energinya lebih
tinggi?
Kandungan C, H dan O
C
H
O
Lemak
77
12
11
Pati
44
6
50






Komponen struktural membran sel
Sebagai sumber energi, umumnya dalam
bentuk trigliserida
Pelarut vitamin yg larut pada lemak
Sebagai prekursor biosintetik ( hormon
steroid dari kolesterol)
Untuk memproteksi (contoh melapisi
ginjal)
Untuk insulasi panas
FUNGSI:
SIFAT UMUM LEMAK
 Relatif tidak larut dalam air
 Larut 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)
LIPID SEDERHANA
Ester 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 KOMPLEKS
Ester 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.
1.
Classification
Bloor’s Classification
A.
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
CH3
CH3
E
E
CH3
E
E
OH
(c) Vitamin A esters
CH3
CH3
(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 cont.
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,
carotenoids)
certain
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
CH2OH
CHOH
CH2OH
Gliserol
HOOC-R
+ HOOC-R ---
HOOC-R
asam lemak
CH2-OOC-R
CH-OOC-R
+ 3H2O
CH2-OOC-R
lemak
air
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-configuration
 Usually R1 and R3 are saturated and R2 is unsaturated
 Natural fats are mixture of two or more simple triglycerides
“ 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:
Jenuh/saturated (CnH2nO2)
2. Tidak jenuh/unsaturated (CnH2n-xO2)

Punya 2 atau lebih molekul H yg
hilang

Esensial bagi tubuh
1.
Most Common Fatty Acids in Di- and
Triglycerides
Fatty acid
Carbon:Double bonds
Double bonds
Myristic
14:0
Palmitic
16:0
Palmitoleic
16:1
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
Cis-9
Sumber : Lehninger,
Sumber : Lehninger,
Fatty Acid Isomers
Forages
Fat content is low: 1 to 4% of dry matter
High proportion of linolenic acid (18:3)
Diglycerides in fats of leaves
Grains
Fat content variable: 4 to 20% of dry matter
High proportion of linoleic acid (18:2)
Triglycerides in oils of seeds
Sumber : Lehninger,
REAKSI KIMIA & SIFAT KHAS LEMAK
1.
A.
B.
HIDROLISIS
ENZIMATIK
trjd dlm pencernaan
DG ALKALI (PENYABUNAN)
Lipida+alkali
gliserol
grm alkali
as.lemak
REAKSI KIMIA & SIFAT KHAS LEMAK
2. 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.
2.
HIDROLITIK
a. Adanya lipase bs menyebabkan reaksi ini,
terbentuk as.lemak+gliserol
b. nilai gizi tdk terpengaruh
OKSIDATIF
a. 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.
An ester forms when a
hydroxyl reacts with a
carboxylic acid, with loss
of H2O.
C H 2O H
H
C
OH
C H 2O H
g lycero l
F orm ation of an ester:
O
R 'O H + H O -C -R "
O
R '-O -C -R '' + H 2 O
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
Sphingolipids are derivatives of the lipid
sphingosine, which has a long hydrocarbon tail, and a
polar domain that includes an amino group.
OH
H 2C
OH
H
C
H 3 N+
CH
CH
HC
O

O
P
O
( CH 2 ) 12

sphingosine
O
H 2C
OH
H
C
H 3N +
CH
CH
HC
(C H 2 ) 1 2
sphingosine -1 -P
CH3
CH 3
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.
CH 3
H 3C
Sphingomyelin has
a
phosphocholine or
phosphethanolamine head group.
Sphingomyelins are common
constituent of plasma membranes
N
+
O
H2
C
H2
C
O
CH 3
P
O

O
phosphocholine
H 2C
sphingosine
O
fatty acid
Sphingomyelin
OH
H
C
CH
NH
CH
C
R
HC
( CH 2 ) 12
CH 3
Sphingomyelin, with a phosphocholine head group, is similar in size and shape to the
glycerophospholipid phosphatidyl choline.
b-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.
Palmitate
(C16)
The subsequent oxidation of
these reaction products by the
citrate cycle and oxidative
phosphorylation generates lots
of ATP.
106 ATP - WOW!
b-oxidation reactions
OXIDATION
The b-oxidation pathway occurs at
the b carbon of the fatty acid,
thereby releasing the C-1 carboxyl
carbon and  carbon as the
acetate component of acetyl CoA.
HYDRATION
OXIDATION
THIOLYSIS
b-oxidation reactions for palmitate (C16)
Palmitoyl-CoA + 7 CoA + 7 FAD + 7 NAD+ + 7 H2O -->
8 acetyl CoA + 7 FADH2 + 7 NADH + 7 H+
ATP currency exchange ratios
31 NADH (31 x ~2.5 ATP) = ~77.5 ATP
15 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
b-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 + PO42- --> ATP + H2O
Ketogenesis
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.
Ketogenesis
Acetyl-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
How many total ATP from
2 acetyl-CoA?
6 NADH
2 FADH2
2 GTP
15 ATP
3 ATP
2 ATP
20 ATP
Ok, now what
happens to these
two acetyl-CoA?
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.
- High density lipoproteins (HDL)
- Low density lipoproteins (LDL)
58
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