Lipids Definition & gen. properties

1. Lipids Definition & gen. properties • Def: lipids are heterogeneous group related to fatty acids. • Lipids are relatively insoluble in water. • They are soluble in nonpolar solvents such as chloroform , diethyl ether, acetone, benzene and ether. • The hydrophobic (water hating) nature of lipids is due to the predominance of hydrocarbon chain.(-CH2-CH2-CH2-) in their structure

3. Function • Lipids are important dietary constituent because: • A) They are a source of high energy value. • B) They contain fat soluble vitamins. • C) They contain essential fatty acids.

4. In the body • Lipids in adipose tissues serve as storage form of energy. • They serve as thermal insulator in the subcutaneous tissues.

5. Cont. • Lipoproteins(a combination of fat and proteins) are important because: • 1. They enter in the structure of cell membrane and mitochondria. • 2. They serve as a transport form of lipids in the blood .

8. Classification of lipids • Simple • Complex • Derived

9. Simple lipids • Simple lipids are esters of fatty acids with various alcohols. • (Ester bond = R-coo-R).They are either fat or waxes. • R-COOH(H) + R-(OH)=> R-COOH-R + H2O

11. Fats • Are esters of fatty acids with glycerol .Fat are either solid or liquid.

13. waxes • Are esters of fatty acids with higher molecular weight alcohols containing one (-OH) group i.e monohydric alcohols.

14. Complex(compound) lipids • Are esters of fatty acids and alcohols ,in addition of other groups . They include: • Phospholipids: they consist of • Fatty acids + alcohols + phosphoric acids residue + nitrogenous base. They include: • Glycerophospholipids : when alcohol is glycerol. • Sphignophospholipids : where the alcohol is sphingosine.

15. Cont. • Glycolipids : they consist of fatty acids + sphingosine + carbohydrate. • Other complex lipids are :which include sulpholipids (containgsuphur) ,amino lipids(containing amino acids) and lipoproteins (containing proteins).

16. Derived lipids • Substance which are given by hydrolysis of simple and complex lipids. • Substance which are insoluble in water but soluble in nonpolar solvents as : • Fatty acids. • Glycerol • Steroids • Alcohols • Ketone bodies • Fatty aldehydes

17. Cont. • Neutral lipids: are those which carry no charge and include: • Neutral fats: (acylglycerols). • Cholesterol and cholesteryl esters.

19. General properties • Water insoluble • They are monocarboxylic • They are mostly aliphatic (not branched) • Fatty acids are present as free fatty acids in plasma. • Fatty acids occur in natural fats contain an even number of carbon atoms , because they are synthesized from 2 carbon units. • Fatty acids may be saturated (containing no double bonds) or unsaturated (containing one or more double bonds).

20. Physical properties • Solubility: • Short chain fatty acids e.g acetic (2C) and butyric (4C) are soluble in water. • Long chain fatty acids are insoluble in water in nonploar solvents. • Melting points: this depend upon length on fatty acids and the degree of unsaturation , so • 1.short chain and unsaturated fatty acids are liquid at RT. • 2.long chain and saturated fatty acids are solid at RT

21. Saturated fatty acids • Have no double bonds in the chain’. • General formula is -CH3-(CH2)n-CooH ,where (n) equals the number of methylene (-CH2) group between the methyl and carboxylic group. • The systemic name of saturated fatty acids ends by the suffix (-anoic).e.gpalmitic acids(16 C) has symmetric name hexadeconic acids(hexa=6;deca10)

23. Unsaturated fatty acids • Have one (monosaturated) or more (polyunsaturated) double bonds in the chain. • The general formulae is Cn-H2n-1-COOH. • The systemic name is unsaturated fatty acids ends by the suffix (-enoic) e.g oleic acids(18C) has systemic name octadecenoic acids (octa=8,deca=10)

24. Non essential fatty acids • They are called non-essential fatty acids because they are synthesized in the body .Thus need not be obtained from the diet. • They can be synthesized from acetyl CoA (Activate acetate) derived from glucose oxidation.

25. Essential fatty acids • They are called essential because they cannot be synthesized in the body . They must be supplied diet • Essential fatty acids include those which contain more than one double bonds (polysaturated fatty acids) e.glinolenic acids and arachidonicacids.This is because there are no human enzyme that can be introduced a double bond except at the ninth carbon atoms(9-10) position.

26. Importance • Normal growth • They enter in the structure of phospholipids and cholesterol esters • Vegetable oil e.g corn oil is rich in essential fatty acids

27. Simple lipids • They are formed only from alcohols and fatty acids.

28. Triayglycerol(triglycerides) • They are called neutral fats because they carry no charge. • The main site for storage of fat in human is the cytoplasm of cells located in subcutaneous fat and around important organs . Adipose tissues is important source of energy .Each gram fat gives 9.3Kcal. • Human fat is liquid at RT and contain high content of oleic acid.

29. Cont. • Butter and lards • Cotton seed oil , linseed oil, sesame oil and olive oil. • Cod liver and shark oil. • In animals • In plants • Marine oil

30. Complex (compound) lipids • These include phospholipids , glycolipids , lipoproteins , sulpholipids , and aminolipids . • Phospholipids :They contain phosphoric acids residues .They are classified into glycerophospholipids (contain glycerol) and sphingophospholipids(contain sphingosine).

31. Lecithin • Structure : • 1. Glycerol • 2. Saturated fatty acid(attached to 1(α) position. • 3.Unsaturated fatty acids (attached to2(β) position. • 4. Choline base (attached to phosphoric acid.) .Base differs in various phopholipids.

32. functions • It enters in the structure of cell membrane .It is most abundant phopsholipid in cell membrane. • It act as body store of choline. Importance of Choline: • 1. It is important in nerve transmitter. • 2. It acts as methyl donor in transmethylation reaction. • 3.Dipalmitoyl lecithine(i.elecithine which contain 2 palmitic acid residue)acts as surfactant in the lung.

33. Cont. • Dipalmitoyllecithinecontinuosly secreted by the lungs cells in the alveolar wall,forming a monolayer over the watery surface of the alveolus and so lower the surface tension .This help expiration and inspiration. • During expiration ,the surfactant becomes solid under pressure . This prevents the adherence of alveolar wall. • During inspiration ,the surfactant makes the lungs easier to expand. • In premature babies :lungs do not secret enough surfactant .This leads to lungs collapse and death from respiratory failure . Treatment of this case need the putting babies in incubator and administration of surfactant locally in the lungs.

34. cephalin • It is one of activating factor of coagulation mechanism

35. Gangliosides • They are called complex glycolipids , because they contain in addition to hexose , one or more sialic acid molecules. • Function: • They acts as receptors at cell membrane • They are present in high concentration in brain.

36. Sterols and steroids • Cholesterol(animal origin) • Ergosterol (plant origin) • Vitamin D group • Bile salt • Steroids hormones • 1.Male sex hormones • 2. Female sex hormones • 3.Adrenal cortical hormones

37. Cholesterol • Distribution in the body: • It is present in all cells especially; • Adrenal cortex. • Liver and kidney • Brain and nerve tissues • The level of blood cholesterol is normally less than 220mg/dl . Any increase above this level is called as hypercholesterolemia.

38. Ergosterol • Structure: similar to cholesterol but differ in • 1.double bonds • 2. the side chain is unsaturated and has extra methyl group. • Properties; • It is plant sterol, poorly absorbed by small intestine. • Function: It gives vitamin D2 by ultra violet rays.

39. Bile salt • Bile salt are bile acids • Function:Bile salts are important for digestion and absorption of lipids.

40. Female sex hormone • Estrogens: 3 types ;estrone , estradiol and estriol. • Site for production: • 1.Ovary and placenta in female • 2.Adrenal cortex in both male and female. • Functions • 1.They stimulate the development of female sex characters and organs.

41. Progesterone • Structure: • Ketone group at C3 • Double bond between C4 and C5. • Methyl group at C10 and C13 • Methylketone at C17 • Site of production: • Ovary and placenta in female. • Adrenal cortex in both male and female • Function: • It prepares the uterus for implantation of the ovum. • It stabilizes pregenancy (prevent abortion)

43. Male sex hormones • Testerone : • Structure • Ketone group at C3 • Double bond between C3 and C5. • 2 methly group at C10 and C13 • -OH at C17. • Site of production: • Intestinal cells of leyding of the testis in male • Adrenal cortex in both male and female. • Function: It stimulates the development of male sex characters and organs.

44. Adrenal cortical hormones • Site of production: • Adrenal cortex • Function: • Glucorticoids :control the metabolism of carbyhydrates , proteins, and fats. • Minerlcorticoids: control the metabolism of Na ,KCl, and water.