Lemak (Pencernaan,Absorpsi dan Metaboisme)
Oleh : Suyatno, Ir. M.Kes (Bagian Gizi – FKM UNDIP Semarang)
Contact: Hp. 08122815730 Blog : suyatno.blog.undip.ac.id E-mail:
[email protected]
Lipids Intake • The most abundant dietary lipids, triglycerides, are found in both animal and plant foods • Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested • Dietary fats consist mainly of triglycerides, which can be split into glycerol and fatty acids. • In many developing countries dietary fats make up a smaller part of total energy intake (often only 8 or 10 percent) • In most industrialized countries the proportion of fat intake is much higher. For example: In the United States average of 36 percent of total energy is derived from fat.
Lipids Functional • Fats in the body are divided into two groups: – storage fat: provides a reserve storehouse of fuel for the body – structural fat : part of the essential structure of the cells, occurring in cell membranes, mitochondria and intracellular organelles.
Klasifikasi Lemak • Terdiri: – Acyl-lipids: mengandung kelompok asam lemak sbg bagian non-polar – Isoprenoids: terdiri 5 unit karbon isoprene
Lipid Subclasses
Fungsi utama Acyl-lipids: komponen membran simpanan fat dan minyak menjaga kelembaban molekul signal (prostaglandin) • Sphingomyelins : komponen membran • • • •
Phospholipids Triacylglycerols Waxes Eicosanoids
: : : :
(cont. dlm lapisan mylein syaraf)
• Glycospingolipids: sell pengenal (antigen gol darah ABO)
Function Utama kelompok isoprenoid: • • • •
Steroids (sterols): Lipid Vitamins : Carotenoids : Chlorophyll :
• Plastoquinone/ ubiquinone • Essential oils
komponen membran, hormon Vitamin A, E, K pigmen kelengkapan fotosintesis pigmen penangkap energi sinar matahari : pembawa elektron yg larut lemak : menthol
Phospholipids
• Phospholipids are built on glycerol back bone. • Two fatty acid groups are attached through ester linkages to carbons one and two of glycerol. • Unsaturated fatty acid often attached to carbon 2 • A phosphate group is attached to carbon three • A polar head group is attached to the phosphate (designated as X in figure)
Triacylglycerols (TAG) (=Triglycerida) • Fats and oils • Impt source of metabolic fuels • Because more reduced than carbos, oxidation of TAG yields more energy (16 kJ/g carbo vs. 37 kJ/g TAG) • Americans obtain between 20 and 30% of their calories from fats and oils. 70% of these calories come from vegetable oils • Insulation – subcutaneous fat is an important thermo insulator for marine mammals
H2C
H C
CH2
O
O
O
C
O
O
C1 C2
C C2
C2 C3
C3
C3
C4
C4
C4 C5
C5
C5
C6
C6
C6 C7
C7
C7
C8
C8
C8 C9
C9
C9
C10
C10
C10
C11
C11
C11
C12
C12
C12
C13
C13
C13
C14
C14
C14
C15 C16 C17 C18
C15
C15
C16
C17 C18
O
C16 C17 C18
Olestra •Olestra is sucrose with fatty acids esterified to –OH groups •digestive enzymes cannot cleave fatty acid groups from sucrose backbone •Problem with Olestra is that it leaches fat soluble vitamins from the body
isoprenoids • Isoprenoids are derived from the condensation of 5 carbon isoprene units • Can combine head to head or head to tail • Form molecules of 2 to >20 isoprene units • Form large array of different structures
Terpenes
Steroids • Based on a core structure consisting of three 6membered rings and one 5-membered ring, all fused together • Triterpenes – 30 carbons • Cholesterol is the most common steroid in animals and precursor for all other steroids in animals • Steroid hormones serve many functions in animals - including salt balance, metabolic function and sexual function
cholesterol • Cholesterol impt membrane component • Function: stabilizes membranes and is a precursor of bile salts and steroid hormones • Only synthesized by animals • Accumulates in lipid deposits on walls of blood vessels – plaques • Plaque formation linked to cardiovascular disease
Cholesterol • Is the structural basis of bile salts, steroid hormones, and vitamin D • Makes up part of the hedgehog molecule that directs embryonic development • Is transported to and from tissues via lipoproteins
Steroids
Many steroids are derived from cholesterol
Asam Lemak (Fatty acids) 18:0
18:1
18:3
• Saturated chains pack tightly and form more rigid, organized aggregates • Unsaturated chains bend and pack in a less ordered way, with greater potential for motion
70o
13o
-17o
Konfigurasi Asam Lemak • Bag polar : karboksil • Bag non-polar: rantai hidrokarbon • Variasi struktuk (>100 tipe): – Beda dlm panjang rantai – Beda dalam derajat ketidakjenuhan (unsaturation) – Beda dalam posisi ikatan rangkap
Penamaan Asam Lemak Menggambarkan: • Jumlah karbon • Jumlah ikatan rangkap • Posisi ikatan rangkap dalam rantai karbon. O C1
C6
C4
C2 C3
C5
C7
C9
C11
C13
C18
C16
C14
C12
C10
C8
C15
HO
C18:1 ∆9 = asam oleat, asam lemak 18 karbon dengan satu ikatan rangkap pada karbon ke 9 dihitung dari atom karbon karboksil (antara karbon ke 9 and 10)
C17
Penamaan Asam Lemak • Notasi Omega (ω ω): hitungan karbon dari akhir rantai hidrokarbon. • Linolenate = 18:3 ∆9,12,15 and 18:3ω ω3,6,9 or 18:3(ω ω-3) O C1
C6
C4
C2 C3
C5
C7
C9
C11
HO
• Linoleate: 18:2ω ω6,9 or 18:2(ω ω-6) • Oleat : 18:1ω ω9 or 18:1(ω ω-9)
C13
C18
C16
C14
C12
C10
C8
C H15
C17
Asam Lemak Esensial: • Tubuh manusia hanya dapat mensintesis ikatanikatan rangkap mulai dari atom no 9 dari ujung omega • Sel tubuh manusia tidak memiliki kemampuan untuk membentuk ikatan rangkap di posisi ω-3 dan ω-6. • Asam lemak linoleat dan asam α-linolenat tidak dapat diproduksi oleh tubuh. • Kekurangan asam lemak esensial dapat menyebabkan: – terjadinya retardasi pertumbuhan, – rambut menjadi kasar, – penurunan kemampuan penyembuhan oleh tubuh (akibat kekurangan asam linolenat) dan – gangguan penglihatan (akibat kekurangan asam asam αlinolenat).
Jenis Lemak Esensial: • Kelompok Omega-3(ω ω3): – Linolenate = 18:3ω ω3,6,9 or 18:3(ω-3) – Turunannya: • Eicosapentaenoat/EPA = 20:5 (ω-3) • Docosahexanoat/DHA = 22:6 (ω-3) • Kelompok Omega-6(ω6): ω6): – Linoleate = 18:2ω ω6,9 or 18:2(ω-6) – Turunannya: • Arachidonate = 20:4 (ω-6)
Asam Lemak Jenuh common name
IUPAC name
melting point (Co)
12:0
laurate
dodeconoate
44
14:0
myristate
tetradeconoate
52
16:0
palmitate
hexadeconoate
63
18:0
stearate
octadeconoate
70
20:0
arachidate
eicosanoate
75
22:0
behenate
docosanoate
81
24:0
lignocerate
tetracosanate
84
Asam Lemak Jenuh common name
IUPAC name
melting point (Co)
16:0
palmitate
hexadeconoate
63
16:1 ∆9
palmitoleate
cis-∆ ∆9-hexadeconoate
-0.5
18:0
stearate
octadeconoate
70
18:1 ∆9
oleate
cis-∆ ∆9- octadeconoate
13
18:2 ∆9,12
linoleate
cis-∆ ∆9,12- octadeconoate
-9
18:3 ∆9,12,15
linolenate
cis-∆ ∆9,12,15- octadeconoate
-17
20:0
arachidate
eicosanoate
75
20:4 ∆5,8,11,14
arachindonate
cis- ∆5,8,11,14-eicosatetraenoate
-49
Pencernaan & Absorpsi Lemak • This action, the digestion or breakdown of fats, is achieved in the human intestine by enzymes known as lipases, which are present primarily in the pancreatic and intestinal secretions. • Garam empedu (Bile salts) from the liver emulsify the fatty acids to make them more soluble in water and hence more easily absorbed.
Proses Pencernaan Lipida Saluran Pencernaan
Proses Pencernaan
1. Mulut
Bercampur dengan kelenjar ludah yang mengandung enzim lipase lingual
2. Esofagus
Tidak ada pencernaan
3. Lambung
• Lipase lingual memulai hidrolisis terbatas: trigliserida menjadi digliserida dan asam lemak • Lemak susu lebih banyak dihidrolisis • Lipase lambung menghidrolisis lemak dalam jumlah terbatas
4. Usus Halus
• Bahan empedu mengemulsi lemak. • Lipase dari pangkreas dan dinding usus halus menghidrolisis lemak dalam bentuk emulsi menjadi digliserida, monogliserida, asam lemak dan gliserol • Fosfolipase dari pankreas menghidrolisis fosfolipid menjadi asam lemak dan lisofosfogliserida. • Kolesterol esterase dari pankreas menghidrolisis ester kolesterol
5. Usus Besar
Sisa lemak dan kolesterol terkurung dlm serat makan dan dikeluarkan melalui feses
Digestion and absorption of lipids is in small intestine • The role of bile salt is: – to stabilize the lipase (a little inhibit) – to emulsify the droplets – to help to form mixed micelles • Colipase : small protein, keep lipase effectively attach to the substrate droplets. • Micelles contain: – free fatty acids – mono-, di-acylglycerols – small amount of TAG – bile salts – phospholipids – fat-soluble vitamins.
Dalam Kantong Empedu, Empedu disimpan
Dalam hati, Kolesterol
Dalam usus halus, Empedu mengemulsi Lemak
empedu
Empedu diabsorbsi kembali ke dalam darah
Empedu dibuang melalui feses Menyebabkan warna feses
Gambar. Sirkulasi entero hepatik empedu
Absorpsi dan Transportasi Lipid • Absorpsi terjadi di jejenum • Asam lemak rantai pendek dan menengah diabsorpsi langsung dalam vena porta dan dibawa ke hati untuk dioksidasi • Kilomikron: lipoprotein pengangkut lipid (terutama trigliserida) dari saluran cerna ke dalam tubuh
Absopsi lipid ke dalam darah Hasil Pencernaan Lipid
Absorpsi
Gliserol Asam lemak rantai pendek (C4-6) Asam lemak rantai menengah (C8-10) Asam lemak rantai panjang Monogliserida
Diserap langsung ke dalam darah
Trigliserida Kolesterol fosfolipida
Diubah menjadi trigliserida di dalam selsel usus halus Membentuk kilomikron, masuk ke dalam limfe kemudian ke dalam darah
VLDL
kilomikron
Usus Halus
Lipid menuju jaringan tubuh melalui lipoprotein lipase
Lipid menuju sel tubuh melalui lipoprotein lipase
Sisa VLDL (IDL)
Hati
Sisa Kilomikron
©
©
© HDL mentransfer LDL
kolesterol dari sel tubuh ke lipoprotein lain untuk digunakan
© HDL
LDL ditarik oleh sel tubuh dengan reseptor apolipoprotein ß-100
LDL ditarik oleh jalur perusak (dlm pembuluh darah)
Dari bermacam sumber
Lipoproteins • High levels of HDL are thought to protect against heart attack • High levels of LDL, especially lipoprotein (a), increase the risk of heart attack
• Lipoproteins are classified as: – HDLs – high-density lipoproteins have more protein content – LDLs – low-density lipoproteins have a considerable cholesterol component – VLDLs – very low density lipoproteins are mostly triglycerides
Lipoprotein yang berperan dlm transport lemak • Kilomikron: mengandung paling banyak trigliserida dan paling sedikit protein sehingga mempunyai densitas paling rendah • VLDL: terdiri atas kurang lebih separuh trigliserida, sehingga mempunyai densitas rendah • LDL: terdiri atas kurang lebih separuh kolesterol, sehingga berpengaruh terhadap lebih 20 penyakit jantung koroner • HDL: terdiri atas kurang lebih separuh lipoprotein, sehingga mempunyai densitas tinggi
Lipoprotein
LDL dan HDL • LDL penting sebagai pengontrol kolesterol • LDL yang melalui jalur sel-sel perusak (scavenger pathway) akan teroksidasi dan tidak bisa masuk lagi ke pembuluh darah • Kolesterol dalam LDL akhirnya menumpuk pada dinding pembuluh darah membentuk plak (plaque) • Plak bercampur dengan protein dan ditutup sel otot dan kalsium menjadi aterosklerosis • HDL mengambil kolesterol dan fosfolipid yang ada dalam pembuluh darah dan menyerahkan ke lipoprotein lain utk dibawa ke hati
Simpanan lemak • Simpanan lemak dalam tubuh di dalam sel lemak dalam jaringan adipos. • Sel-sel adipos mempunyai enzim khusus pada permukaannya, yaitu lipoprotein lipase (LPL) yang dapat melepas trigliserida dan lipoprotein, menghidrolisisnya dan meneruskan hasil hidrolisis ke dalam sel. • Di dalam sel terdapat enzim lain yang merakit kembali bahan-bahan hasil hidrolisis menjadi trigliserida untuk disimpan sbg cadangan energi. • Sel-sel adipos menyimpan lemak bilamana kilomikron dan VLDL yang mengandung lemak melewati sel-sel tersebut.
Simpanan lemak
Lipid Metabolism
Lipid Metabolism • Most products of fat metabolism are transported in lymph as chylomicrons • Lipids in chylomicrons are hydrolyzed by plasma enzymes and absorbed by cells • Only neutral fats are routinely oxidized for energy • Catabolism of fats involves two separate pathways – Glycerol pathway – Fatty acids pathway
Lipid Metabolism • Glycerol is converted to glyceraldehyde phosphate – Glyceraldehyde is ultimately converted into acetyl CoA – Acetyl CoA enters the Krebs cycle
• Fatty acids undergo beta oxidation which produces: – Two-carbon acetic acid fragments, which enter the Krebs cycle – Reduced coenzymes, which enter the electron transport chain
Lipid Metabolism
Lipogenesis and Lipolysis • Excess dietary glycerol and fatty acids undergo lipogenesis to form triglycerides • Glucose is easily converted into fat since acetyl CoA is: – An intermediate in glucose catabolism – The starting molecule for the synthesis of fatty acids
Lipogenesis and Lipolysis • Lipolysis, the breakdown of stored fat, is essentially lipogenesis in reverse • Oxaloacetic acid is necessary for the complete oxidation of fat – Without it, acetyl CoA is converted into ketones (ketogenesis)
lipogenesis
lipogenesis
lipolysis
Lipogenesis and Lipolysis
Lipogenesis and Lipolysis
Supported Enzyme
(PUFA)
Lipid Metabolism: Synthesis of Structural Materials
• Phospholipids are important components of myelin and cell membranes • The liver: – Synthesizes lipoproteins for transport of cholesterol and fats – Makes tissue factor, a clotting factor – Synthesizes cholesterol for acetyl CoA – Uses cholesterol to form bile salts
• Certain endocrine organs use cholesterol to synthesize steroid hormones
Lipid Metabolism • Digestion - Hydrolysis Reaction
Lipid Metabolism
Lipid Metabolism
Fatty Acid Oxidation • Initial Step: Requires an ATP to synthesize acetyl CoA with the fatty acid.
Beta Oxidation
Beta Oxidation
Beta Oxidation
Beta Oxidation
Beta Oxidation
Beta Oxidation
Beta Oxidation
Palmitic Acid Review
Palmitic Acid -ATP Synthesis • • • • • •
Palmitic Acid is C-16 Initiating Step - requires 1 ATP (text says 2) Step 1 - FAD into e.t.c. = 2 ATP Step 3 - NAD+ into e.t.c. = 3 ATP Total ATP per turn of spiral = 5 ATP Example with Palmitic Acid = 16 carbons = 8 acetyl groups • Number of turns of fatty acid spiral = 8-1 = 7 turns • ATP from fatty acid spiral = 7 turns and 5 per turn = 35 ATP. • NET ATP from Fatty Acid Spiral = 35 - 1 = 34 ATP
Palmitic Acid (C-16) -ATP Synthesis • NET ATP - Fatty Acid Spiral = 35 - 1 = 34 ATP • • • • • • • • • • •
Review ATP - Citric Acid Cycle start with Acetyl CoA Step ATP produced 7 visible ATP 1 Step 4 (NAD+ to E.T.C.) 3 Step 6 (NAD+ to E.T.C.) 3 Step10 (NAD+ to E.T.C.) 3 Step 8 (FAD to E.T.C.) 2 NET 12 ATP per turn C.A.C. 8 Acetyl CoA = 8 turns C.A.C. 8 turns x 12 ATP/C.A.C. = 96 ATP GRAND TOTAL 130 ATP
Acetyl CoA
Ketone Bodies
Ketone Bodies
Lipogenesis
