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 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
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
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
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
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
Top Related