Biochemistry (XII)

Carbohydrates and its biomedical Importune & types   

Carbohydrates are natural macromolecules including a large number of relatively heterogenous compounds containing C, H and O and are the most abundant biomolecuels on the earth. They are commonly called sugars or saccharides (Latin; saccharum meaning sugar).

Carbohydrates are defined as the polyhydroxy (polyhydric) aldehydes or polyhydroxy ketones or other compounds (large polymeric compounds) that yield these derivatives (i.e. polyhydroxy aldehydes or ketones) upon hydrolysis. Carbohydrates are regarded as the Hydrates of Carbon because the ratio of O and H as same as it is in water (i.e. in the ratio of 2:1). Their general formula is C_x(H₂O)_y. glucose, galactose, fructose, sucrose, lactose, maltose, starch, cellulose, glycogen etc are some typical carbohydrates.

CHO           | H –   C – OH           |          CH2OH	CH2OH | C = O | CH2OH	CHO           |   H –  C – OH           | HO – C – H           |   H – C – OH           |   H – C – OH           |          CH2OH	CHO           |   H –  C – OH           | HO – C – H           | HO – C – H           |   H – C – OH           |          CH2OH	CHO           | HO – C –H           | HO – C – H           |    H – C – OH           |   H – C – OH           |          CH2OH	CHO           |           C = O           | HO – C – H           |   H – C – OH           |   H – C – OH           |          CH2OH
Glyceraldehyde	dihyroxyacetone	D-glucose	D-galactose	D-mannose	D-fructose

Carbohydrates are regarded as the Hydrates of Carbon because many of them contain H and O in the same proportion as in water (i.e. in the ratio of 2:1) and that is why they may be represented by a general formula C_x(H₂O)_y or C_xH_2yO_y (where x = 3 or some large number). However, this definition proved to be erroneous because:

1)Some compounds such rhamnose (C₆H₁₂O₅), Menitol (C₆H₁₄O₆) etc are definitely carbohydrates but their formulae do not conform to the general formula C_x(H₂O)_y.

2) All compounds conforming to the general formula are not necessarily carbohydrates e.g.             formaldehyde, HCHO (CH₂O), acetic acid, CH₃COOH [C₂ (H₂O)₂] etc.

Bio-medical Importance of Carbohydrates

1.	Regulation of metabolism	(Ribose, C5h10O5 and deoxyribose, C5H10O4)
2.	Genetic regulation	(DNA and RNA; hereditary carriers)
3.	Dietary Source	(Sugar, Starch, glucose)
4.	Energy Source	(Glucose)
5.	Storage Function	(glycogen)
6.	Extra Energy source for animals	(Cellulose)

Classification of Carbohydrates on the basis of Taste

1. Sugars; Sweet, crystalline and water-soluble e.g Glucose, fructose 2. Non- sugars; Tasteless, amorphous and water-insoluble e.g. Starch, cellulose

(1).   Sugars

The crystalline water soluble carbohydrates which are sweet in taste are called sugars. All monosaccharides and disaccharides are sweet in taste and hence monosaccharides and disaccharides are commonly called sugars. e.g. Glucose, fructose, sucrose, maltose etc.

(2).   Non-sugars

The amorphous water insoluble tasteless carbohydrates are called non-sugars. All polysaccharides are non-sugars. e.g. starch, cellulose etc. are non-sugar carbohydrates.

Classification of Carbohydrates on the basis of Free Aldo or Keto Group

1.	Reducing Sugars	;	Contains free aldo or keto group	e.g.	glucose, galactose, fructose, maltose
2.	Non-reducing sugars	;	Lacks free aldo or keto group	e.g.	Sucrose ,Starch, cellulose

Reducing Sugars

Reducing Sugars are those sugars that contain free aldehydic or ketonic group (along with adjacent – OH group) and they can reduce mild oxidizing agents like Benedict’s reagent [alkaline solution of citrate complex of copper (II)], Fehling’s Solution [alkaline solution of tartarate complex of copper (II)] or Tollen’s reagent [ammonical silver nitrate solution]. All monosaccharides and all disaccharides except sucrose are reducing sugars. E.g. glucose, galactose, fructose, maltose, lactose.

Non-reducing sugars

Non-reducing Sugars are those sugars, which do not contain free aldehydic or ketonic group, and they cannot reduce mild oxidizing agents like Benedict’s reagent, Fehling’s Solution or Tollen’s reagent. e.g. One disaccharide (e.g. Sucrose) and all polysaccharides (e.g. starch, cellulose etc)are non-reducing sugars.

Classification of Carbohydrates Based on Molecular Structure or Complexity 

Based on complexity of molecular structure, behaviour on hydrolysis and number of carbon atoms or the number of simple sugar units present in their molecules, carbohydrates are classified into following three major classes:

1.	Monosaccharides(Simple sugars)	(Non-hydrolyzable reducing sugars; containing 3-9 carbons atoms with general formula CnH2nOn or (CH2O)n )
2.	Oligosaccharides (e.g. Disaccharides)	(hydrolyzable reducing sugars (except sucrose); giving 2-10 simple sugars)
3.	Polysaccharides	(hydrolyzable non-reducing tasteless amorphous non-sugars; which are macromolecular high molecular mass natural polymers giving more than 10 simple sugars on hydrolysis)

           

Monosaccharides

1.  These are the simplest carbohydrates and are non-hydrolyzable simple sugars that cannot be further hydrolyzed into simpler carbohydrate units consisting of aldoses or ketoses. [The monosaccharides having aldehydic group are aldoses (e.g. glucose) while monosaccharides containing ketonic group are called ketoses (e.g. fructose). The aldehydic group being monovalent is always present at the end of the carbon chain while ketonic group being divalent can be present anywhere in the carbon chain but in naturally occurring monosaccharides the keto group is present at carbon number 2].

  

2.   They are also known as reducing sugars because they have free sugar (i.e. aldehydic or ketonic) group, so they can reduce Benedict’s Reagent (citrate complex of Cu²⁺ ions), Fehling’s Solution (tartarate complex of Cu²⁺ ions) and Tollen’s reagent (ammonia complex of Ag⁺ ions).

3.   They have the general formula C_nH_2nO_n or (CH₂O)_n where n is the number of carbon atoms ranges 3-9 (3-10). Hence they are named as trioses, tetroses, pentoses and hexoses depending upon the number of 3, 4, 5 and 6 carbon atoms respectively. e.g. aldopentoses (ribose, arabinose, xylose) aldohexoses (e.g. glucose, galactose, mannose) ketopentoses (ribulose), ketohexoses (e.g fructose  or levulose etc.) [Ose is the suffix for aldo sugar and Ulose is the suffix for keto sugars].

4.  Sugars with five carbon atoms (pentoses) or six carbon atoms (hexoses) are more stable as cyclic structures than as open chain structures.

5.   Among hexoses glucose, galactose, mannose and fructose are important from nutritional and muscular physiological point of view. Among pentoses ribose, arabinose (obtained from Gum-Arabic) and xylose (wood’s component) and deoxyribose play an important part in human metabolism.

Oligosaccharides

1. These are carbohydrates which are formed when 2-10 (2-9) monosaccharide units condensed together through glycosidic linkage by the loss of water molecule. Conversely the carbohydrates which give 2-10 (2-9) simple sugar (monosaccharide) units on hydrolysis by water (in the presence of an acid or by enzymes). Among oligosaccharides, the most important is disaccharides  are important.

2. Disaccharide is formed by the joining (condensation) of two molecules of same or different monosaccharides units through glycosidic linkage by giving out a water molecule and thus on hydrolysis disaccharide yield two units of simple sugars. e.g. Maltose, lactose, sucrose. They are commonly known as saccharose having the general formula C₁₂H₂₂O₁₁.

3.   Except sucrose, all disaccharides are reducing sugars.

Polysaccharides

Polysaccharides are carbohydrates of high molecular mass that yield more than 10 monosaccharides units upon hydrolysis and are made up of long chains of many monosaccharides units joined to each other through glycosidic linkage in a linear or branched structure by the process of polymerization. They are non-sugars, water-insoluble, tasteless amorphous solids. Their principal functions are food storage (energy storage compounds) and structural building of cells. e.g. Starch, cellulose, glycogen (animal starch), chitin.

Glycosidic Linkage

Glycosidic linkage is the characteristic of oligosaccharides (disaccharides etc.) and polysaccharides as it joins two or more glycosides (monosaccharides). [Disaccharides are formed by a condensation reaction between two monosaccharides accompanied by the elimination of a water molecule].

A Glycosidic Linkage is one in which a carbon atom is joined to two oxygen atoms through single bond (i.e. -O - C - O -) which differs from ether linkage (> C - O - C< ) in that, in the latter, oxygen is joined to two carbon atoms while in glycosidic linkage one of the carbon atom is attached to two oxygen atoms.

Formation of glycosidic linkage between hydroxyl groups of the hemiacetals of a–glucose and b– glucose units at C–1 and C–4 condense to form a disaccharide called maltose. This O - C - O linkage is called a,b-1:4-glycosidic linkage

There are following types of glycosidic linkages:

1.	a,b-1:4-glycosidic linkages	(in maltose)	[b-glucose and a-glucose]
2.	b-1:4-glycosidic linkages	(in lactose)	[b-glucose and b-galactose]
3.	a,b-1:2-glycosidic linkages	(in sucrose)	[a-glucose and b-fructose]

D-Sugars and L-Sugars

The D and L-forms of an isomer (enantiomer) is related to standard glyceraldehydes whose two forms are arbitrarily assigned the absolute configurations. The glyceraldehyde in which penultimate asymmetric carbon atom has hydroxyl group to the right and hydrogen to the left is designated as D-form while the glyceraldehydes in which penultimate asymmetric carbon atom has hydroxyl group to the left and hydrogen to the right is designated as L-form. If the configuration at the penultimate (the lowest or farthest from the top) asymmetric carbon atom of a compound is related to D-glyceraldehyde, it is designated as D-form and it is related to L-glyceraldehyde, it is designated as L-form. (The symbols D and L signify the arrangement of atoms or groups in space and are not related to the property of the molecule to rotate the plane of polarized light towards right or left).

CHO         | H – C – OH         |        CH2OH	CHO           | HO – C – H           |          CH2OH
D-glyceraldehyde (D-configuration)	L-glyceraldehyde (L-configuration)
( - OH group on the right side of chiral C)	( - OH group on the left side of chiral C)

In case of compounds with several asymmetric carbon atoms like sugars, the first asymmetric carbon atom from the bottom (i.e. penultimate chiral C) is always taken as the reference carbon atom for absolute designations. As per convention for sugars, the carbon atom-5 is taken as the reference atom for D-L designations.

All those sugars in which the first asymmetric carbon atom from the bottom i.e. penultimate chiral carbon has –OH group on right hand side are termed as D-sugars while those sugars in which –OH group is on the left hand side at the first asymmetric carbon atom from the bottom are referred as L-sugars. Most of the natural sugars have D-configuration. Naturally occurring glucose is D-glucose.

CHO           |   H –  C – OH           | HO – C – H           |   H – C – OH           |   H – C – OH           |          CH2OH	CHO           |   H –  C – OH           | HO – C – H           | HO – C – H           |   H – C – OH           |          CH2OH	CHO           | HO – C –H           | HO – C – H           |    H – C – OH           |   H – C – OH           |          CH2OH	CHO           |           C = O           | HO – C – H           |   H – C – OH           |   H – C – OH           |          CH2OH
D-glucose	D-galactose	D-mannose	D-fructose

Dextrorotatory and Laevorotatory Form and Mutarotation

Different forms of a compound which resemble in their chemical and most physical properties but differ in their optical behaviour towards the plane polarized light are called optical isomers and the phenomenon is called optical isomerism.

The optical isomers which are related to each other as object and its mirror image are called enantiomers.

The enantiomer (optical isomers) which rotates the plane of polarized light to the right is called dextrorotatory and is conventionally given a positive sign (+) and described by d. The mirror image of enantiomer (optical isomer) which rotates the plane of polarized light to the left is called Laevorotatory and is conventionally assigned a negative sign (-) and denoted by l. e.g. D-glucose is dextrorotatory and hence is called dextrose and D-fructose is laevorotatory and hence is called Levulose (Laevulose).

The spontaneous change in the specific rotation of an optically active compound involving the dynamic interconversion of two isomeric closed chain structures into one another via open chain form is called mutarotation. These two closed chain isomers are called a and b forms which differ only in the orientation of the hydroxyl group at carbon atom-1. The closed chain structure of an optically active compound in which –OH group is on right hand side at carbon number 1 (anomeric or glycosidic carbon) is called a-isomer and when –OH group is on the left hand side at carbon number 1 is termed as b-isomer. Such pairs of optical isomers differing in the orientation of H and OH groups only at carbon atom-1 (anomeric or glycosidic carbon) are called anomers. E.g. D-glucose exists as two anomeric forms a-glucose and b-glucose which are separate crystalline forms with different melting points and optical rotation but when either form of glucose is dissolved in water, it gets converted into the other form and an equilibrium mixture is formed of a-glucose and b-glucose together with a very small amount of open chain form i.e.

	a,D (+) glucose =		Open chain form D(+) glucose  =		b,D (+)glucose
	m.p. =146°C				m.p.= 150°C
	36%		0.02%		64%
	+110°		+52.5°		+19.7°
	CHO                      |     H –C–OH                     | HO – C – H                |                   H – C – OH               |                    H – C – OH             |          CH2OH				CHO                      |   H –  C – OH                     | HO – C – H                |                   H – C – OH               |                    H – C – OH             |          CH2OH

Proteins (its Definition, Importance and Types)

Definition of Proteins 

All proteins yield amino acids which are generally a-amino carboxylic acids of different molecular sizes, upon complete hydrolysis. Thus, amino acids are the basic constructing units of proteins. The human body probably contains at least 10,000 different kinds of proteins. The proteins constitute 50% of the dry weight of the living cells (that is why they have given a name of proteins derived from the Greek work proteios meaning of prime importance). Proteins are present in all living organisms and are found in muscles, skin, hair, nails and other tissues that make up the bulk of the body’s non-bony structure.

Proteins (derived from Proteios meaning first) are the complex nitrogenous long chains polymeric organic macromolecules of very high molecular weight (34000- 5000000 dalton or 17500 -6,000,000 Da) which are giant linear condensation biopolymers of a-amino acid monomers (ranging from 200-6,0000) interlocked or linked together through peptide linkages (acid-amide bonds) through condensation polymerization with the elimination of water molecules. In other words, Proteins are high molecular weight organic polypeptides which yield a- amino acids upon complete hydrolysis. [The aggregation of two or more amino acids linked together through peptide bond is called Peptide. A dipeptide is a condensation product of two amino acids containing a single peptide bond while a tripeptide is a condensation product of three amino acids containing two peptide bonds. A condensation product of 10 or more amino acids is called Polypeptide]. A polypeptide of high molecular weight more than 10,000 da containing more than 200 amino acids is called protein.

All proteins contain the elements C, H, O, N and S. Other elements like P and traces of other elements such as Ca, Fe, Mn, Cu, Zn and I may be the essential constituents of some specialized proteins. e.g. Casein (milk protein) contains Ca and P, haemoglobin (iron containing protein).

Bio-medical Importance of Proteins

1.	Building and maintenance of body tissues	(Structural proteins)
2.	Catalytic Function/ Biochemical Catalysis	(Enzymatic proteins or Enzymes)
3.	Regulation of metabolism	(Hormonal proteins like insulin)
4.	Contraction of muscles	(Contractile proteins like Actin and myosin filaments)
5.	Storage Function	(Storage proteins like Lipoproteins, ferritin)
6.	Protective Function	(Immunal proteins like Antibodies like globulins and γ-globulins)
7.	Respiratory Function/ Oxygen carrier	(Haemoglobin, cytochrome, haemocyanin, myoglobin)
8.	Genetic Regulation	(Genetic proteins or nucleoproteins like DNA and RNA)

Classification of Proteins Based on Physio-Chemical Properties

Proteins are of three types:

1.	Simple proteins	;	Consist of only amino acids or their derivatives e.g. Albumin, globulin
	(a) Albumins		(e.g. egg albumin, serum albumin, milk albumin/lactalbumin, Wheat albumin, leucosin
	(b) Globulins		(e.g. egg globulin, serum globulin, myosin/muscle globulin, amandin in almonds
	(c) Glutelins		(e.g.
	(d) Gliadin/Prolamine		(e.g. hordein in barley, zein in maze corn, gliadin in wheat)
	(e) Albuminoids		(e.g. casein & collagen in tendons, keratin in hair, horn, nails)
2.	Conjugated Proteins	;	Consist of simple proteins with prosthetic group e.g. Haemoglobin,
	(a) Glyco-proteins
	(b) Lipo-proteins
	(c) Nucleo-proteins
	(d) Phospho-proteins
	(e) Chromo-proteins
3.	Derived Proteins	;	Degraded proteins e.g. Proteoses, polypeptides, peptides, peptones.

 1).Simple Proteins

These are the simplest proteins which upon hydrolysis yield only amino acids and their derivatives. e.g. egg albumin, serum albumin of blood, and milk albumin (lactalbumin) etc.

2). Conjugated Proteins

These are the proteins which consist of simple proteins with non-proteinous substance called prosthetic group. e.g. Haemoglobin, Chlorophyll.

3). Derived Proteins

These are not naturally occurring proteins and are obtained by degradation of proteins by acids, alkalis, heat, enzymes or biochemical action. e.g. peptones, proteoses, polypeptides, peptides.

 Amino Acids and its Types

Definition and General Formula

Amino acids are the basic building blocks of proteins. Amino acids are bifunctional (polyfunctional) organic acids having both an acidic carboxyl group (-COOH) and a basic amino group (-NH₂ or >NH) along with distinct side chain R (which is different for different amino acids). Almost all the naturally occurring amino acids are a-amino acids in which amino group is attached to a-carbon atom (relative to the carboxyl group). They have following general formula:

    

Where R may be hydrogen, a straight or branched chain alkyl group or an aryl group.

The amino group in amino acids may be present at any carbon atom other than that of carboxyl group containing carbon (i.e. a– carbon). Based on whether the amino group is present on the a, β or γ - carbon atom relative to the carboxyl group, amino acids are referred to as a, β and γ–amino acids respectively.  

Bio-medical Importance of Amino Acids

1.	Protein synthesis
2.	Hormones synthesis
3.	Energy Source
4.	Regulation of metabolism

Types of Amino Acids Based on their Acidity or Alkanity

1.	Neutral amino acids	;	contain one –NH2 & one –COOH group.	e.g.	Glycine, alanine, Valine, Leucine
2.	Acidic amino acids	;	contain more than one –COOH groups.	e.g.	Aspargine, Glutamine
3.	Basic amino acids	;	contain more than one –NH2 groups	e.g.	Lysine, Arginine.

Essential Amino Acids and Non-essential Amino Acids

About 20 amino acids have been identified as the constituents of most of the animal and plant proteins. Out of 20 amino acids which are required for protein synthesis, the human body can synthesize only 10 and such amino acids are called Non-essential amino acids. e.g. Glycine, alinine, proline, aspartic acid, glutamic acid, tyrosine, serine, cysteine, aspargine.

The ten amino acids that are not synthesized by human body and hence are needed to be provided in the diet for proper health and growth are called Essential Amino Acids. [They are 10 for infants and 8 for adult human being]. They include Valine, Leucine, Isoleucine, Lysine, Methionine, Threonine, Arginine, Tryptophan, Phenylalanine, and Histidine (last two are needed for infants).

Zwitterion

The dipolar but overall electrically neutral charged ion with positive as well as negative ends within the same molecule is termed as Zwitterion (German; two ions). The dipolar ionic structure is also called internal salt. All a–amino acids exist largely as dipolar ionic forms or Zwitterions in solution that is formed when the proton goes from the acidic carboxylic group (on ionization) to basic amino group (Lewis base).

Due to the Zwitter ions form, amino acids are soluble in water but insoluble in organic solvents. The Zwitterion formation makes amino acids amphoteric and allows them to donate or accept proton from the medium or solvent in which they are dissolved.

Peptide Linkage

The acid-amide (-CO -NH -) bond through which amino acids are linked in proteins by eliminating a water molecule is called Peptide Linkage. This linkage is formed by the removal of a water molecule b/w an -NH₂ group of an amino acid and -COOH group of another. The product formed from condensation of two amino acids containing a single peptide linkage is called Dipeptide. The product formed from condensation of three amino acids containing two peptide bonds is called Tripeptide.

Lipids and its Types Definition of Lipids The lipids are a group of heterogenous water insoluble non-polar organic compounds of the plant and animal origins which are soluble in Bloor’s reagent (a mixture of diethyl ether and ethyl alcohol in the ratio of 2:1) e.g. Oils, fats, waxes, butter, fat-soluble vitamins (A, D, E, K) etc. Bio-medical Importance of Proteins 1. Energy Supply 2. Insulation of vital organs 3. Regulation of optimum body temperature Types of Lipids on the basis of structures by Bloor 1. Simple Lipids or Glycerides a)    Fats and Oils b)    Waxes (Triglycerides)             (Monoglyceride) [C15H31-COO-C30H61]          2. CompoundsLipids/Conjugated Lipids  a)    Phospholipids or Phosphoglycerides b)    Glycolipids           c)    Lipoproteins (Phosphate derivatives of lipids) (Carbohydrate derivatives of lipids) (Protein derivatives of lipids) 3. Steroids (non-saponifiable fats) a)    Cholesterol [C27H45OH] b)    Cholic acid [C24H40O5] c)    Progesterone [C21H30O2] d)    Vitamin D             A) Fats and Oils (Triglycerides or triacylglycerols) Fats and oils are simple lipids that are triesters of fatty acids (long chain carboxylic acids containing even number of carbon atoms) with polyhydric alcohol, glycerol. Hence they are also called Triglycerides or Triacylglycerol. Difference b/w Fats and Oils Fats 1.   Fats are solid state esters (triglycerides) of fatty acid and glycerol at room temperature.          2.   Fats usually come from animal sources. 3.   Fats contain a higher proportion of saturated fatty acids in their esters. 4.   Fats have low iodine number (less unsaturation). 5.   Usually fats are simple glycerides in which all the three –OH groups of glycerol are esterified with same acid. Oils 1.         Oils are liquids state esters (Triglycerides) of fatty acids and glycerol at room temperature. 2.         Oils come from vegetable sources. 3.         Oils contain a higher proportion of unsaturated fatty acids in the in their esters. 4.         Oils have high iodine number (except coconut and fish oils.). 5.         Usually oils are mixed glycerides containing two or more different fatty acid parts. B) Waxes Waxes are naturally occurring esters of long–chain monohydric alcohols and long-chain fatty acids (C16 or greater). Thus on hydrolysis wax gives monohydric alcohol [while fat gives trihydric alcohol, glycerol]. They are water-insoluble, flexible, non-reactive, low melting solids with a waxy feeling. e.g. Bee’s wax is an ester of palmitic acid and mericyl alcohol (C30H61OH) and its chemical name will be mericyl palmitate. CH3.(CH2)14.COO.(CH2)29.CH3 OR C15H31COOC16H33, spermacetic wax C15H31COO-C16H33 (Spermaceti consists principally of cetyl palmitate (the ester of cetyl alcohol, C16H33OH and palmitic acid), C15H31COO-C16H33). Cetyl alcohol, also known as 1-hexadecanol and palmityl alcohol, is a fatty alcohol with the formula CH3(CH2)15OH. At room temperature, cetyl alcohol takes the form of a waxy white solid or flakes. The name cetyl derives from the whale oil (Latin: cetus) from which it was first isolated. Simple and Mixed Glycerides When the three OH group of glycerol are esterified with the same acid, the triglyceride is known as Simple Glyceride (Simple Fat). If two or more OH groups of glycerol are esterified with different fatty acids, then the triglyceride is known as Mixed Glyceride or Mixed triglycerides or Mixed triacylglycerols (Mixed Fats). Cooking oils and fats are mixed triglycerides containing all the three different fatty acids.

Fatty Acids and its Types

Fatty acids are naturally occurring non-branched aliphatic monocarboxylic acids consisting of a long saturated or unsaturated hydrocarbon chain with a terminal carboxylic group mostly obtained from hydrolysis of natural fats and oils containing even number of carbon atoms (ranges C₁₂-C₂₀).

Saturated and Unsaturated Fatty acids

The alkyl groups of saturated fatty acids contain C-C single bond.e.g.

1.	Lauric acid	(C11H23-COOH/C12H24O2)	C12H24O2
2.	Myristic acid	(C13H27-COOH/ C14H28O2)
3.	Palmitic acid	(C15H31-COOH/ C16H32O2)
4.	Stearic acid	(C17H35-COOH/ C18H36O2)

The alkyl group of unsaturated fatty acids contain at least C=C double bond. e.g

1.	Oleic acid/9-Octadecenoic acid(C17H33-COOH/ C18H34O2)	CH3(CH2)7CH=CH(CH2)7COOH
2.	Linoleic acid/ 9,12-Octadecadienoic acid(C17H31-COOH/ C18H32O2)	CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
3.	Linolenic acid/9,12,15-octadecatrienoic acid(C17H29-COOH/ C18H30O2)	CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH
4.	Arachidonic acid/5,8,11,14-Eicosatetraenoic acid	(C19H31-COOH/ C20H32O2)

Essential Fatty acids

Essential Fatty acids are those fatty acids that our body cannot synthesize so they must be taken as diet. The function of essential fatty acids is:

ii.          They prevent deposition of cholesterol in arteries and veins.

ii.          They help in reproductive functions and blood clotting.

All essential fatty acids are unsaturated i.e.:

i.          Linoleic acid           (C₁₇H₃₁-COOH)

ii.          Linolenic acid         (C₁₇H₂₉-COOH)

iii.         Arachidonic acid    (C₁₉H₃₁-COOH)

Chemical Properties of Fats and Oils

1. Saponification

The alkaline hydrolysis of fats or oils on boiling with a solution of strong alkali (NaOH or KOH) to form sodium or potassium salt of long chain fatty acid (soap) along with glycerol is called Saponification. It is the reverse process of esterification of glycerol.

                                                 

2. Rancidification

The development of disagreeable foul smell and unpleasant bad taste in a fat or oil caused by its hydrolysis or oxidation on exposure to warm, moist air for a long time is called Rancidification or Rancidity. E.g. when butter is left uncovered, the butter fat tributyrin is hydrolyzed by microorganisms in air producing butyric acid, which imparts unpleasant offensive odour and makes it off-taste. Rancidification is due to:

i.    Hydrolysis of ester linkage to give original fatty acid of sour taste.

ii.    Oxidation at double bond forming volatile aldehydes of bad odour.

3. Iodine Number

The degree of unsaturation of a fat or oil is usually measured by Iodine Number that is the number of gram of iodine consumed or absorbed by 100 gram of fat or oils. Higher the iodine number, greater would the degree of unsaturation or vice versa.

The iodine number of oils is generally higher than fats (due to higher proportion of unsaturated acids in it).

The iodine number of vegetable fats is generally higher than animal fats (except coconut and fish oil).

4. Hydrogenation of Oils

The hydrogenation of unsaturated vegetable oils such as cotton seed oil converts it into fats. Hydrogenation of vegetable oils takes place in the presence of Ni catalyst. 

Vitamins, its Types, Sources and Deficiency Diseases

Vitamins are the complex organic compounds which act as a catalysts or promoters and facilitate the metabolic processes required in very small amount. They cannot be synthesized by the animals hence they must be supplied in diet. They have no food value but they are also called Accessory Food Factors b/c they regulate various physiological and chemical reactions taking place in the body. [So far 13 vitamins have been isolated. Thiamine was the first vitamin discovered].

Classification of Vitamins on the Basis of Solubility 

Dr Inam Ul Haq Jazbi