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 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. Lipids in adipose tissues serve as storage form of energy. They serve as thermal insulator in the subcutaneous tissues. 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 . Simple Complex Derived 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 Are esters of fatty acids with glycerol .Fat are either solid or liquid. Are esters of fatty acids with higher molecular weight alcohols containing one (-OH) group i.e monohydric alcohols. 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. Glycolipids : they consist of fatty acids + sphingosine + carbohydrate. Other complex lipids are :which include sulpholipids (containg suphur) ,amino lipids(containing amino acids) and lipoproteins (containing proteins). 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 Neutral lipids: are those which carry no charge and include: Neutral fats: (acylglycerols). Cholesterol and cholesteryl esters. 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). 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 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.g palmitic acids(16 C) has symmetric name hexadeconic acids(hexa =6;deca10) 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) 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. 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.g linolenic acids and arachidonic acids.This is because there are no human enzyme that can be introduced a double bond except at the ninth carbon atoms(9-10) position. Normal growth They enter in the structure of phospholipids and cholesterol esters Vegetable oil e.g corn oil is rich in essential fatty acids They are formed only from alcohols and fatty acids. 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. In animals Butter and lards In plants Cotton seed oil , linseed oil, sesame oil and olive oil. Marine oil Cod liver and shark oil. 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). 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. 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.e lecithine which contain 2 palmitic acid residue)acts as surfactant in the lung. Dipalmitoyl lecithine continuosly 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. It is one of activating factor of coagulation mechanism 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. 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 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. 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. Bile salt are bile acids Function:Bile salts are important for digestion and absorption of lipids. 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. 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) 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. Site of production: Adrenal cortex Function: Glucorticoids :control the metabolism of carbyhydrates , proteins, and fats. Minerlcorticoids: control the metabolism of Na ,KCl, and water.
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