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 Definition & gen. properties

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.

Function

Lipids in adipose tissues serve as storage form of energy.

They serve as thermal insulator in the subcutaneous tissues.

In the body

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 .

Cont.

Simple Complex Derived

Classification of 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

Simple lipids

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

Fats

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

waxes

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.

Complex(compound) lipids

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).

Cont.

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

Derived lipids

Neutral lipids: are those which carry no charge and include:

Neutral fats: (acylglycerols). Cholesterol and cholesteryl esters.

Cont.

Water insoluble They are monocarboxylic acid containing 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).

General 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

nonpolar 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

Physical properties

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)

Saturated 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)

Unsaturated 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.

Non 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.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.

Essential fatty acids

Normal growth They enter in the structure of phospholipids

and cholesterol esters Vegetable oil e.g corn oil is rich in essential

fatty acids

Importance

They are formed only from alcohols and fatty acids.

Simple lipids

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.

Triayglycerol(triglycerides)

In animals

In plants

Marine oil

Butter and lards

Cotton seed oil , linseed oil, sesame oil and olive oil.

Cod liver and shark oil.

Cont.

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).

Complex (compound) lipids

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.

Lecithin

lecithin

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.

functions

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.

Cont.

It is one of activating factor of coagulation mechanism

cephalin

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.

Gangliosides

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

Sterols and steroids

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.

Cholesterol

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.

Ergosterol

Ergosterol

Bile salt are bile acids Function:Bile salts are important for

digestion and absorption of lipids.

Bile salt

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.

Female sex hormone

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)

Progesterone

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.

Male sex 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.

Adrenal cortical hormones