Lemak

Lemak (Pencernaan,Absorpsi dan Metaboisme)

Oleh : Suyatno, Ir. M.KesOleh : Suyatno, Ir. M.Kes(Bagian Gizi – FKM UNDIP Semarang)

Contact: Hp. 08122815730

Blog : suyatno.blog.undip.ac.idE-mail: [email protected]

Lipids Intake• The most abundant dietary lipids, triglycerides, ar e 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 • In many developing countries dietary fats make up a smaller part of total energy intake (often only 8 or 10 per cent)

• In most industrialized countries the proportion of fat intake is much higher. For example: In the United States average of 36 per cent 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 bodythe 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 – Isoprenoids: terdiri 5 unit karbon isoprene

Lipid Subclasses

Fungsi utama Acyl-lipids:

• Phospholipids : komponen membran• Triacylglycerols : simpanan fat dan minyak• Waxes : menjaga kelembaban• Eicosanoids : molekul signal• Eicosanoids : molekul signal

(prostaglandin)• Sphingomyelins : komponen membran

(cont. dlm lapisan mylein syaraf)• Glycospingolipids: sell pengenal

(antigen gol darah ABO)

Function Utama kelompok isoprenoid:

• Steroids (sterols): komponen membran, hormon

• Lipid Vitamins : Vitamin A, E, K

• Carotenoids : pigmen kelengkapan fotosintesis

• Chlorophyll : pigmen penangkap energi sinar• Chlorophyll : pigmen penangkap energi sinar

matahari

• Plastoquinone/ : pembawa elektron yg larut lemak

ubiquinone

• Essential oils : menthol

Phospholipids

• Phospholipids are built on glycerol back bone.• Two fatty acid groups are attached through • 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)

CH2

HCH2C

O O

C OC1

O

C2

C3

C4

C5

C6

C7

C8

C2

C3

C4

C5

C6

C7

O

C O

C2

C3

C4

C5

C6

C7

C8oxidation 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

C9

C16

C8

C10

C11

C12

C13

C14

C15

C17

C18

C9

C16

C8

C10

C11

C12

C13

C14

C15

C17

C18

C9

C16

C8

C10

C11

C12

C13

C14

C15

C17

C18

Olestra

•Olestra is sucrose with fatty acids esterified to –OH groups

•digestive enzymes cannot cleave fatty acid groups from sucrose 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 • Form large array of different structures

Terpenes

Steroids• Based on a core structure consisting of three 6-membered rings and one 5-membered ring, all fused together

• Triterpenes – 30 carbons

• Cholesterol is the most common steroid in animals • 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• 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 developmentthat directs embryonic development

• Is transported to and from tissues via lipoproteins

Steroids

Many steroids are derived from cholesterol

Asam Lemak (Fatty acids)

• Saturated chains pack tightly and form more rigid, organized aggregates

• Unsaturated chains bend

18:0 18:1 18:3

• 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 dlm panjang rantai

– Beda dalam derajat ketidakjenuhan (unsaturation)

– Beda dalam posisi ikatan rangkap

Penamaan Asam Lemak

C C C

Menggambarkan:

• Jumlah karbon

• Jumlah ikatan rangkap

• Posisi ikatan rangkap dalam rantai karbon.

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)

C1

C2C3

C4C5

C6C7

C8C9

C10C11

C12C13

C14C15

C16C17

C18O

HO

Penamaan Asam Lemak

• Notasi Omega (ωωωω): hitungan karbon dari akhir rantai hidrokarbon.

• Linolenate = 18:3 ∆∆∆∆9,12,15 and 18:3ωωωω3,6,9or 18:3(ωωωω-3)or 18:3(ωωωω-3)

• Linoleate: 18:2ωωωω6,9 or 18:2(ωωωω-6)• Oleat : 18:1ωωωω9 or 18:1(ωωωω-9)

C1

C2C3

C4C5

C6C7

C8C9

C10C11

C12C13

C14CH15

C16C17

C18O

HO

Asam Lemak Esensial:• Tubuh manusia hanya dapat mensintesis ikatan-

ikatan 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 • 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 α-

linolenat).

Jenis Lemak Esensial:

• Kelompok Omega-3(ωωωω3): – Linolenate = 18:3ωωωω3,6,9 or 18:3(ωωωω-3) – Turunannya:

• Eicosapentaenoat/EPA = 20:5 (ωωωω-3)

• Docosahexanoat/DHA = 22:6 (ωωωω-3)

• Kelompok Omega-6(ω6):ω6):ω6):ω6):– Linoleate = 18:2ωωωω6,9 or 18:2(ωωωω-6)– Turunannya:

• Arachidonate = 20:4 (ωωωω-6)

Asam Lemak Jenuh

common name IUPAC name melting point (C o)

12:0 laurate dodeconoate 44

14:0 myristate tetradeconoate 5214:0 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 namemelting point(Co)

16:0 palmitate hexadeconoate 6316:0 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.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 LipidaSaluran

PencernaanProses Pencernaan

1. Mulut Bercampur dengan kelenjar ludah yang mengand ung enzim lipase lingual

2. Esofagus Tidak ada pencernaan

3. Lambung • Lipase lingual memulai hidrolisis terbatas: triglis erida menjadi digliserida dan asam lemak

• Lemak susu lebih banyak dihidrolisis• Lipase lambung menghidrolisis lemak dalam jumlah • 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 es ter kolesterol

5. Usus Besar Sisa lemak dan kolesterol terkurung d lm 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 tothe substrate droplets.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 usus halus,Empedu

mengemulsi Lemak

Dalam hati,Kolesterol

Lemak

Empedu dibuang melalui fesesMenyebabkan warna feses

empedu

Empedu diabsorbsi kembalike dalam darah

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 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

GliserolAsam lemak rantai pendek (C4-6)Asam lemak rantai menengah

Diserap langsung ke dalam darah

Asam lemak rantai menengah (C8-10)

Asam lemak rantai panjangMonogliserida

Diubah menjadi trigliserida di dalam sel-sel usus halus

TrigliseridaKolesterolfosfolipida

Membentuk kilomikron, masuk ke dalam limfe kemudian ke dalam darah

Usus Halus kilomikronVLDL

Sisa VLDL(IDL) Hati Sisa Kilomikron

Lipid menuju jaringantubuh melaluilipoprotein lipase Lipid menuju sel

tubuh melalui lipoprotein lipase

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HDLLDL

Dari bermacam sumber

HDL mentransfer kolesterol dari sel tubuh ke lipoprotein lain untuk digunakan

LDL ditarik oleh jalurperusak (dlm pembuluhdarah)

LDL ditarik oleh sel tubuh dengan reseptor apolipoprotein ß-100

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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(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 – 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 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 • 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 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 • 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 – 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: acetyl CoA is: – An intermediate in glucose catabolism – The starting molecule for the synthesis of fatty

acids


• Lipolysis, the breakdown of stored fat, is essentially lipogenesis in reverse

• Oxaloacetic acid is necessary for the complete oxidation of fatcomplete oxidation of fat– Without it, acetyl CoA is converted into

ketones (ketogenesis)

lipogenesis

lipolysis

Supported Enzyme

(PUFA)

• Phospholipids are important components of myelin and cell membranes

• The liver: – Synthesizes lipoproteins for transport of cholesterol

Lipid Metabolism: Synthesis of Structural

Materials

– 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

Fatty Acid Oxidation• Initial Step: Requires an ATP to synthesize

acetyl CoA with the fatty acid.

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 • 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• 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

Lipogenesis

Lemak

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