Importance of organic compounds – in Biological system.

2.1 Definition of organic and inorganic compounds:

• Organic compounds are chemical compounds compose of carbon atoms bonded with hydrogen, oxygen, nitrogen, sulphur and other elements. Organic compounds are mainly associated with living organism. They are characterised by their covalent bonds.

• Inorganic compounds are chemical compounds derived from the minerals, non living sources or synthetic processes. Inorganic compounds are not composed of carbon hydrogen bonds (C-H bonds).

2.2 Importance of organic compounds – in Biological system.

Organic compounds play very important roles in the biological system. These are followings

• 1. Structure of biological system: Biological systems are composed of proteins, carbohydrates, lipids, and nucleic acids.

• 2. Cell membrane: Cell membranes are composed of phospholipids. These membranes act as barrier to separate internal and external environment of cells. They control movement of molecules into cells and out of cells.

• 3. Enzymes and hormones: Enzymes are hormones stimulate chemical reactions inside human body. These chemical reactions take place for normal functioning of biological system. These enzymes and hormones are chemically proteins.

• 4. Energy sources: Biochemical reactions require energy to perform normal functions. Carbohydrates are main source of energy.

• 5. Metabolic reactions: Chemical reactions inside biological system are called metabolism. Metabolic reactions require organic compounds to complete the chemical reactions inside biological system.

• 6. Immunity: Power of body to resists infection is called immunity. Antibodies develop immunity inside biological system. Chemically, these antibodies are protein.

• 7. Genetic information: Biological system stores genetic information inside DNA. Chemically, DNA is nucleic acid.

2.3 Basic chemistry of carbohydrates, proteins and lipids - Their nutritional effect in humans.

Basic chemistry of Carbohydrates: Carbohydrate is aldehyde or ketone derivative of polyhydroxy alcohol or compound which yields these derivatives on hydrolysis.are organic compounds composed of carbon (C).

Classification of carbohydrates: Carbohydrates are classified into following classes on the basis of unit sugar(saccharide)

• 1. Monosaccharide: Monosaccharides are simplest carbohydrates. They cannot be further hydrolysed to smaller sugars. General formula of monosaccharide is (CH2O)n. “n” represents number of carbon atoms in the monosaccharides eg. of common monosaccharide are glucose, fructose, and galactose. Monosaccharide is basic building block of complex carbohydrates.

  • If monosaccharide contains aldehyde functional group it is aldose.(Glucose)

  • If monosaccharide contains ketone functional group it is ketose.(Fructose)

2. Disaccharide: Disaccharide consists of two monosaccharide molecules. Both monosaccharide molecules are connected with glycosidic bonds.

General formula Cn(H2O)n-.eg

• · Sucrose: It is commercial sugar. Sucrose consists of two monosaccharides. These two monosaccharides are connected with glycosidic bonds between C1 of α- glucose and C2 of beta-fructose. It is a non-reducing sugar because the reducing group of glucose &fructose is used in glycosidic bond formation.

• · Maltose: It is present in malt, known as malt sugar. It is formed by two α-D-glucose units., connected with the glycosidic bond between C1 of α- glucose and C4 of another α- glucose unit, It is reducing sugar, the presence of a free aldehydic group at C1 of second glucose.

• Lactose: It is known as milk sugar. It is formed by the combination of β-D-galactose and β-D-glucose. The glycosidic bond formed between C1 of galactose and C4 of glucose. Thus it also reduces sugar.

3. Oligosaccharide: Oligosaccharide consists of three or more monosaccharide molecules. Hydrolysis of oligosaccharides produces three or more molecules of monosaccharide. eg. raffinose.

4. Polysaccharide: Polysaccharide consists of more than ten molecules of monosaccharide. Hydrolysis of polysaccharides produces more than ten molecules of monosaccharide.General formula is (C6H12O6)n.They are not sweet and are also called non-sugar.

Polysaccharides are further classified into

a)Homopolysaccharides: Homopolysaccharides are made up of a single kind of monosaccharides. eg. Starch, Glycogen, & cellulose.

• · Starch: Plants store glucose as starch as a source of energy. It consists of a long chain of glucose monomers joined in α 1,4 linkages. Starch is made up of two chemicals: Amylose, a soluble portion of starch. (10-20%), Amylopectin, an insoluble portion of starch(80-90%)

  • Structure of amylose: Amylose is an unbranched long-chain polymer in amylose, glucose is linked together through α 1,4 glycosidic linkage and has two ends, one is the reducing end and the other is the non-reducing end.

  • Structure of amylopectin: Amylopectin is a branched long chain of glucose. Glucose molecules attach with carbon at 4 and also carbon at 6.

• Glycogen: Animals store glucose as glycogen as a source of energy. It is found in the liver and muscles. It consists of a large number of glucose molecules. They are highly branched polysaccharides. Glucose molecules are linked together α 1,4 glycosidic linkage. At the branching point glucose molecules are linked together through α 1,6 glycosidic linkage

• Cellulose: Cellulose is a structural component of plant cell walls. It is an unbranched long chain of glucose linked together through β1-4 glycosidic linkage

b)Heteropolysaccharide: Heteropolysaccharides are made up of different monosaccharides. eg. Heparin. 

Nutritional /biological effects of carbohydrates on humans:

• 1. Carbohydrate is the main source of energy

• 2. Many body fluids like cerebrospinal fluid and synovial fluid have carbohydrate constituents and act as lubricants.

• 3. Heparin is a mucopolysaccharide that acts as an anticoagulant.

• 4. Glycogen is storage form of carbohydrate(glucose)store in liver .

• 5. Carbohydrates are a source of energy as reserve sugar. eg. Glucose as blood sugar, Fructose as fruit sugar, Lactose as milk sugar,& Sucrose as cane sugar.

• 6. Glycerol is an important component of fat known as sugar alcohol.

Basic chemistry of proteins:

Proteins are complex organic molecules composed of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S). The basic chemistry of proteins includes structure, composition, and their interactions.

Structure and composition of proteins: Proteins are composed of amino acids. Amino acids are building blocks of protein molecules. Protein molecules consist of 20 different amino acids. or Proteins are high molecular weight polymers of α amino acids joined together with peptide bonds (Covalent bonds).

1. Amino acid: Each amino acid consists of one central carbon atom (alpha carbon) bonded to four different chemical groups:

• • Amino group: (-NH2).

• • Carboxyl group: (-COOH),

• • Hydrogen group: (-H),

• • Variable R group (Sidechain).

2. Peptide bond: Protein molecule consists of amino acids. Amino acids bind with each other by peptide bonds. The Carboxyl group of one amino acid combines with an amino group of another amino acid. This results in the elimination of water molecules and a peptide bond (amide bond )is formed. In which the hydrogen atom of NH2, the amino group is replaced by the Variable R group, the Peptide bond is a covalent bond. The linkage of amino acids with each other develops a long chain structure called a Polypeptide chain.

The number and order of amino acids in the polypeptide chain is the primary structure of protein. The simplest combination of two amino acids combined with peptide bonds is called dipeptide. The molecule contains two peptide bonds with three amino acids called tripeptides, containing three peptide bonds called tetrapeptide. A molecule containing ten peptide bonds is called a polypeptide. A polypeptide having more than 100 amino acid residues & molecular mass of more than 10,000 is known as a protein.

Classification of protein:

Proteins can be classified into the following two classes on the basis of their shape:

a)Fibrous protein: Fibrous protein looks like fiber. In this protein polypeptide chains run parallel. These are insoluble in all common solvents, water, and salt solutions. organic solvents. eg. Keratin.

b)Globular protein: In globular protein the polypeptide chain coils around to give a globular (round) shape. These are soluble one or two common solvents

On the basis of structure and shape, there are four levels of organization:

1. Primary structure: The linear arrangement of amino acids in protein structure is called primary structure. The specific arrangement of amino acids determines the unique structure and function of that amino acid.

2. Secondary structure: The folding pattern of long chains of amino acids in protein structure is the secondary structure of proteins. These coiled structures held together disulfide or hydrogen bonds. The secondary structure exists in two forms α- helix and β- pleated sheet

   • Alpha(α) helical structure: Twist in long chain of amino acids in protein structure forms spiral or helical shape.

   • Beta(β) pleated sheets: Protein chain folding backs develops sheet-like structure.

3. Tertiary structure: Three-dimensional folding of polypeptide chain develops a globular shape. This is the tertiary structure of the protein. The tertiary structure is stabilized by several types of bonds. These are hydrogen bonds, ionic bonds (bonds between charged ions), disulfide bonds (covalent bonds between sulfur atoms), and hydrophobic interactions.

4. Quaternary structure: Some proteins consist of multiple polypeptide subunits. These polypeptide subunits come together to form a quaternary structure. Interaction between these polypeptide subunits decides the overall functions of the protein.

Types of proteins based on composition/solubility:

1. Simple protein: Proteins that contain only amino acids. eg.

   • Albumin: These are soluble in water, and coagulated by heat. eg. Serum protein

   • Globulin: These are soluble in a dilute solution of strong acid and base. , coagulated by heat. eg. Serum globulin

2. Conjugated protein: The protein that has a non-proteinous part (prosthetic group) along with a proteinous part. eg. Haemoglobin: In haemoglobin, heme is a non-proteinous part(prosthetic group)and globin is a proteinous part.

3. Derived protein: These proteins are formed by denaturation and coagulation from simple & conjugated proteins. eg Fibrin: Fibrinogen is a soluble plasma protein Fibrin is formed from fibrinogen by chemical reactions.

PROPERTIES OF PROTEIN:.

· Denaturation: A change in the three-dimensional structure of protein molecules is called denaturation of protein. Heat, extreme pH levels or exposure to certain chemicals cause protein denaturation. Protein loses its biological functions after denaturation. eg. the heating of raw eggs causes coagulation of egg contents. This is due to the denaturation of protein in an egg. The denaturation of protein is an irreversible process.

· Biuret reaction: Peptide linkages of proteins react with biuret reagent (an alkaline 0.02%) cupric sulphate solution containing Na-K-tartrate to form a purple-coloured complex. The depth of colour formed is directly

Biological functions of protein: There are several types of protein inside the biological system. The proteins perform the following functions

• 1. Enzymes: All enzymes are proteinous in nature. They catalyse biochemical reactions

• 2. Hormones: Chemically, hormones are proteins. They catalyse biochemical reactions,

• 3. Structural protein(Collagen): Collagen in connective tissues is protein. Collagen is a fibrous protein.

• 4. Transport protein(Haemoglobin): Chemically, Haemoglobin consists of globin and haem. Globin is a protein. Haemoglobin transports respiratory gases., O2 &CO2.

• 5. Antibodies: Chemically, antibodies are proteins. Antibodies develop immunity.

• 6. Blood buffers: Serum protein acts as an amphoteric compound. It can combine with both acid and base at the normal pH of blood it acts as acid.

Basic chemistry of lipids:

Lipids are composed of carbon (C), hydrogen (H), and oxygen (H). Some lipids also contain phosphorus (P) and nitrogen (N). Lipids are organic molecules characterized by their hydrophobic (water-repellent) property. They are insoluble in water and soluble in organic solvents.

Classification:

• 1. Simple lipid

• 2. Compound lipid

• 3. Derived lipid

1. Simple lipid: Simple lipids are esters of fatty acid with various alcohols, generally glycerol. Simple lipids are of two types:

· Fats: Esters of fatty acids with glycerol, also known as neutral fat or triglycerides. Fat in a liquid state at room temperature is called oil.

· Waxes: Esters of fatty acids with higher molecular weight monohydric alcohol.

2. Compound lipid: Esters of fatty acids containing another group in addition to alcohol and fatty acids. They are further divided into:

   • Phospholipid: Contains fatty acids, glycerol, phosphoric acid, and a nitrogenous base.

   • Glycolipids: Lipids containing fatty acids, sphingosine, and carbohydrate.Complex lipid

3. Derived lipids: These include substances derived from simple lipids or compound lipids on hydrolysis. eg. Fatty acid, glycerol& steroid.

Fatty Acids

Fatty acids: Fatty acids are the building blocks of lipids. Each fatty acid is composed of hydrocarbon chains. Hydrocarbon chains of fatty acids are composed of a long chain of carbon atoms with a carboxyl group at one end (-COOH). The nature of fatty acids in lipids decides the chemical properties of lipids. There are two types of fatty acids.

Saturated fatty acids: Saturated fatty acids consist of a saturated hydrocarbon chain. Hydrocarbon chains containing only single bonds are called saturated hydrocarbon. General formula, CnH202. eg. Butyric acid, palmitic acid.

Unsaturated fatty acids: Unsaturated fatty acids consist of an unsaturated hydrocarbon chain. Hydrocarbon chains containing one or more double bonds are called unsaturated hydrocarbons. General formula,CnH2n-2XO2. It may be further divided as----

a) Monounsaturated fatty acids: Fatty acid contains one double bond. eg. Oleic acid.

b) Polyunsaturated fatty acids: Fatty acid contains two or more double bonds. Polyunsaturated fatty acids are also called essential fatty acids. These fatty acids are not synthesized in the body. eg. Linoleic acid.

Triglycerides (Triacylglycerols): Triglycerides are the most common type of lipid in the biological body. Triglycerides are composed of three fatty acid molecules. These fatty acid molecules are bonded with the glycerol molecules through ester bonds. During this process, three molecules of water are released.

When glycerol combines with two molecules of fatty acids it forms diglycerides. when glycerol combines with one molecule of fatty acids, it forms monoglycerides. All these three fatty acids are similar in pure fat. One, two, or three fatty acids are dissimilar in mixed fat. Commercially fats are of two types.

• · Hard fat: They are true fats. They are solid at 20 degrees C. They have a low melting point. It is hard above 20 degrees C due to presence of long chain saturated fatty acids. eg. Ghee &butter.

• · Oils: Oils are also true fats. Which are liquid at 20○C due to the presence of unsaturated fatty acids. eg. Mustard oil &coconut oil.

Phospholipids

The chemical structure of phospholipids and triglycerides are similar. Two fatty acids and one phosphorus group are attached to a glycerol molecule in phospholipids. Phospholipids molecule has one polar end called the hydrophilic end or head of phospholipids molecule. Another end of phospholipid molecules is a nonpolar end called the hydrophobic end or tail of phospholipid molecules. Phospholipids form a lipid bilayer in the cell membrane.

Functions:

• · Phospholipids are the main lipid constituent of plasma/cell.

• · Phospholipids are an important constituent of nervous tissue, brain, and muscles.

• · It helps in the formation of platelets and Thus plays an important role in blood coagulation.

• · Lecithine is an effective surface active agent. It is present in the inner surface of the lungs. It prevents adherence.

Sterols

Sterols are derived from lipids and belong to the steroid group. Steroids are a group of tetracyclic lipid derivatives

Structure: Steroid has three hexane rings and one pentane ring. Skeleton has 17 carbon atoms with two methyl groups at 18 and 19. Sterols are alcoholic derivatives of steroids. group at position 3)

.eg.Cholesterol,ergasterol,sitosterol etc.

Cholesterol: It is fat-soluble white crystalline sterol or steroid alcohol C27H45OH. It has four fused hydrocarbon rings i.e. hexane ring and one pentane ring. It bears -OH group at position 3. Eight carbon aliphatic chains are present at position 17. Cholesterol is mainly found in animal fat and absent in plant fat. It is synthesized in the liver and adrenal cortex. It is present in blood in two forms free and esterified form. Normal concentration in blood varies from 140-250mg/100 ml.

Function:

• · Cholesterol is a component of all cell membranes in animals

• · It helps in the formation of bile salts and bile acids.

• · It transports fat to the liver for metabolism.

• · It forms steroid hormones in the adrenal gland

• It forms vitamin D in the skin under sun rays.

Properties of Lipid(Fat or oil):

• 1. Hydrolysis: Hydrolysis of lipids by the action of the enzyme lipase produces fatty acid and glycerol.

• 2. Saponification: Hydrolysis of lipids by alkali is called saponification. Saponification of fats or oils produces glycerol and alkali salt of fatty acid (soap)

• 3. Hydrogenation: Hydrogenation of unsaturated fats in the presence of a catalyst(nickel)is called hardening. It is a commercial method to convert plant fat into hard fat(vegetable ghee).

• 4. Rancidity: It is a chemical change to produce an unpleasant taste and odor in fat, due to oxidation and hydrolysis by exposure to air and moisture.

Nutritional/Biological functions of lipid/Fat

• 1. Source of energy: Fats act as a source of energy. It yields 9.3Kcal/gm, Carbohydrates yield 4.5Kcal/gm. Fats give more energy than carbohydrates.

• 2. Fat-soluble vitamins: It helps to supply fat-soluble vitamins A, D E & K.

• 3. Myelin sheath: it is found around medullated nerve fiber (Nervous system)

• 4. Cell membrane: Lipids bilayer are the main component of the cell membrane.

• 5. Essential fatty acids: Fats provide essential fatty acids which cannot be synthesized in the body

• 6. Blood platelets: Blood platelets have phospholipid, which helps in blood clotting.

• 7. Insulation: Fats present in adipose tissue below the skin, act as thermal insulators.

• 8. Shock-absorbing cushion: Fats surround vital organs of the body and act as shock-absorbing cushion

Dr Pramila Singh