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LIPIDS . Digestion .. Absorption .. Transportation .. Metabolism. Dina Trabzuni. Lipids consist of two parts Glycerol Fatty Acids a. Saturated fatty acids b. Unsaturated fatty acids . Monounsaturated . Polyunsaturated. Figure 3 : Formation of TG. Table 1 : Saturated fatty acids .

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Digestion .. Absorption ..

Transportation .. Metabolism

Dina Trabzuni

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Figure 3 : Formation of TG

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Table 1 :Saturated fatty acids

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Table 2 :Unsaturated fatty acids

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  • Lipids are classified as simple or complex

  • Simple lipid

  • a.Fatty acids

  • b. neutral fats (monoglyceride,

  • diglycerde, and triglyceride)

  • c. waxes

  • Complex lipids

  • a. Phospholipids

  • b. Glycolipids

  • c. Lipoproteins

  • 3. Derived lipids

Figure 1 : Triglyceride

Figure 2 : Phosphatidic acid

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Function of Fat

. Energy

. Essential nutrient

. Flavor and Satisfaction

. Adipose Tissue

.Cell membrane Structure

Fat in Food

Fat in Body

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Food Sources of Fat

. Meat Fat (bacon, sausage….)

. Dairy Fats and products (cream, butter, cheese..)

. Egg yolk

. Monounsaturated , polyunsaturated Fatty acid

.Vegetable oil (safflower, corn, soybean, cottonseed, olive oil)

Animal Fats

Plant Fat

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Characteristics Of Food Fat Sources

. Butter, margarin, salad oils and dressing,shirteninig fat meat

. Chees, cream portion of homogenised milk, egg yolk, nuts, seeds, olives…..

Visible Fat

Invisible Fat

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Digestion of lipids

  • In mouth

  • mechanical digestion Lingual Lipase

  • In stomach

  • mechanical digestion

  • Gastric lipase

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Pancreatic lipase



2 fatty acids + Mono glycerides

1 fatty acids + Diglycerides

Pancreatic lipase


3 fatty acids + glycerol

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Absorption of lipids

Figure 4 : Absorption of fat.

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Transportation of lipids

Table 3Lipids are transported in the plasma as lipoproteins.

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Lipids Metabolism

. Liver and Adipose tissue play a central role in lipid metabolism.

. Adipose tissue is the main store of triglyceride in the body.

. Lipid metabolism either lipolysis or lipogenesis.

. Fatty acids are both oxidized to acetyl CoA and synthesized from acetyl CoA.

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. Complete hydorlysis of triglyceride yeild gelycerol and 3 fatty acids.

. Fatty acids oxidiation take place in the mitochonderia.

. Fatty acids are activated before being catabolized (oxidized).

Fatty acid + ATP + CoA

Acyl CoA + AMP + PPi

acyl CoA


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Long chain fatty acids penetrate the inner -Mitochinderial membrane as carnitine derivatives.

Figure 5 : Role of carnitine in the transport of long chain fatty acids.

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β - oxidation pathway of fatty acids membrane as carnitine derivatives.

. Many tissues are capable of oxidizing fatty acids in the mitochondria by β - oxidation pathway.

. The chain is broken between the α (2) and β (3) carbon atoms.

Figure 6 : Overview of β - oxidation pathway of fatty acids

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β - oxidation of fatty acids ( membrane as carnitine derivatives. Figure 7)

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The products of oxidation of fatty acids membrane as carnitine derivatives.

Oxidation of fatty acids produces a large quantity of ATP,

.example : Palmitic acid (C:16 )

7 cycles from 7 NADH + 7 FADH2

(7 x5 = 35 ATP)

7 cycles from 8 Acetyl CoA

(8 x 12 = 96 ATP)

2 ATP for the initial activation

of fatty acid

( 35 +96 – 2 = 129 molecule of ATP)

Figure 8 : acetyl CoA product

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Ketone bodies - oxidation pathway (figure9)

Ketogenesis occurs when there is a high rate of fatty acid oxidation in the Liver (figure 10).

Acetyl CoA

Acetyl CoA


Aceto acetyl CoA



β -hydroxy butyrate


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Lipogenesis - oxidation pathway (figure9)

. The body is capable of synthesizing fatty acids in the cytoplast of the cell from starter ( acetyl CoA + malonyl CoA).

. Malonyl CoA is formed from Acetyl CoA

Figure 11 : Biosynthesis of Malonyl CoA

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. - oxidation pathway (figure9) Acetyl CoA transfer to the cytoplast across the mitochondrial membrane in the form of citrate

Figure 12 : Conversion the citrate to Oxaloacetate and Acetyl CoA.

. The enzymes involved in fatty acid synthesis are arranged in a complex called the fatty acid synthase system.

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The steps in the synthesis of fatty acid ( - oxidation pathway (figure9)Figure 13)

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Cholesterol - oxidation pathway (figure9)

. Cholesterol is not an energy producing nutrient.

  • . It is an essential structural

  • component of membrane of the outer layer of plasma lipoprotien.

  • Bile acids and steriod hormones are formed from cholesterol.

  • . Cholesteryl ester is a storage form of cholesterol which is found in most tissues.

Figure 14 : Cholesterol

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Acetyl CoA - oxidation pathway (figure9)


Acetyl CoA






Acetyl CoA is the source of all carbon atoms in cholesterol

Acetoacetyl CoA

β -hydroxy- β- methylglutaryl CoA



Farmesyl pyrophosphate

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References - oxidation pathway (figure9)

Brene, R., Levy, M., Koeppen, B., Stanton, B., (2004) Physiology, Fifth edition. Mosby.

Fox, S., (2004) Human Physiology, Eighth edition. Mc Graw Hill.

Hunt, S., Groff, J., (1997) Advanced Nutrition and Human Metabolism, West Puplishing Company.

Lehninger, A., Nelson, D., Cox, M.,(1993) Principles of Biochemistry, 2nd edtion. Worth Puplishers.

Murray, R., Granner, D., Mayes, P., Rodwell, V., (1996) Haper’s Biochemistry, 24th edition, Prentic-Hall International, Inc.

Seeley, R., Stephens, T., Tate, P., (1992) Anatomy and Physiology,Mosby Yearbook.

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Thank you - oxidation pathway (figure9)