11th Class Biology Biomolecules / जैव-अणु Micromolecules

These are molecules of low molecular weight and have higher solubility. These include minerals, water, amino acid, sugars and nucleotides. All molecules or chemicals functional in life activity are called biomolecules.

(1) Elements : On the basis of presence and requirement in plants and animals, they are grouped into major \[(Ca,P,Na,Mg,S,K,N)\] and minor \[(Fe,Cu,Co,Mn,Mo,Zn,I)\] bioelements.

On the basis of function, they may be of following types :–

(i) Framework elements : Carbon, oxygen and hydrogen.

(ii) Protoplasmic elements : Protein, nucleic acid, lipids, chlorophyll, enzymes, etc.

(iii) Balancing elements : Ca, Mg and K.

(2) Biological compounds

(i) Inorganic compounds : Water 80%, inorganic salts 1-3%.

(ii) Organic compounds : Carbohydrates (1.0%), Lipids (3.5%), Proteins (12.0%) Nucleotides (2.0%), Other compounds (0.5).

(3) Cellular pool : Aggregated and interlinked  various kinds of biomolecules in a living system. So cell is called cellular pool. It includes over 5000 chemicals. Inorganic chemicals are present mostly in aqueous phase while organic in both, aqueous and non-aqueous. Cellular pool comprises of both crystelloid and colloidal particles. Hence called as crystal colloids.

(4) Water : Liquid of life, major constituent of cell (about 60-90%) and exists in intracellular, intercellular and in vacuoles. In cells it occurs in free state or bound state (KOH, CaOH etc.).

Properties of water : It is colourless, transparent, tastless and odourless, neutral (pH-7) liquid.  It is universal solvent, as it can dissolve both polar and non-polar solutes. High boiling point due to hydrogen bonding. Shows high degree of cohesion and adhesion. It can undergo three states of matter i.e., solid\[\rightleftharpoons \]liquid\[\rightleftharpoons \]gas.  It is dense and heaviest at 4C and solid below it.

(5) Carbohydrates : e.g., sugars, glycogen (animal starch), plant starch and cellulose.

Source of carbohydrate : Mainly photosynthesis. It exists only in 1% but constitutes 80% of the dry weight of plants.

Composition : It consists of carbon, hydrogen and oxygen in the ratio \[{{C}_{n}}{{H}_{2n}}{{O}_{n}}.\] It is also called saccharide and sugars are their basic components. Classification of carbohydrates are :

(i) Monosaccharides : These are single sugar units which can not be hydrolysed furthur into smaller carbohydrates. General formula is \[{{C}_{n}}{{H}_{2n}}{{O}_{n}},\]e.g., Trioses-3C, (Glyceraldehyde, dihydroxyacetone etc.), tetroses-4C, pentoses-5C, hexoses-6C etc.

Important Hexoses

Glucose : \[{{C}_{6}}{{H}_{12}}{{O}_{6}}.\] Grape sugar is dextrose. Grape is sour due to presence of tartaric acid. Fructose is called fruit sugar (sweetest among natural sugars) and glucose is called "sugar of body" (blood sugar). Normal level of blood glucose is 80-120mg/100ml. If it exceeds then condition is called "glucosuria".

Fructose : Occurs naturally in fruit juices and honey. Hydrolysis of cane sugar in body also yields fructose.

Galactose : It is called as brain sugar. It's an important constituent of glycolipids and glycoproteins.

Properties of monosaccharide

• Monosaccharides are colourless, sweet tasting, solids and show oxidation, esterification and fermentation.
• Due to asymmetric carbon, they exist in different isomeric forms. They can rotate polarized light hence they are dextrorotatory and laevorotatory.
• D-glucose after reduction gives rise to a mixture of polyhydroxy alcohol, sorbitol or mannitol.

Functions of monosaccharides

• Glucose is the ultimate source of ATP in the cell respiration.
• Polymerisation of these molecules forms macromolecules.
• Ribose and deoxyribose are constituent of nucleic acids and nucleotides.
• Sugars have free aldehyde or ketone group which can reduce \[C{{u}^{++}}\]to \[C{{u}^{+}}\] and are called reducing sugars. Benedicts or Fehling's test are used to confirm the presence of reducing sugars.

(ii) Oligosaccharides : Formed due to condensation of 2-10 monosaccharide units, the Oxygen bridge is known as "glycoside linkage" and water molecule is eliminated. The bond may be \[\alpha \] and \[\beta .\]

(a) Disaccharides : Composed of two molecules of same or different monosaccharide units. Also called "double sugars". Molecular formula is \[{{C}_{12}}{{H}_{22}}{{O}_{11}}.\]

Maltose : Also called "malt sugar" stored in germinating seeds of barley, oat, etc. It is formed by enzymatic (enzyme amylase) action on starch. It is a reducing sugar.

Sucrose : "Cane sugar" or " table-sugar". Obtained from sugarcane and beet root and on hydrolysis splits into glucose and fructose.

Lactose : Milk sugar or 5% in mammalian milk. On hydrolysis yields glucose and galactose. Streptococcus lacti converts lactose in to lactic acid and causes souring of milk.

(b) Trisaccharides : Composed of three molecules of sugars. Molecular formula is \[{{C}_{18}}{{H}_{32}}{{O}_{16}}.\]

Raffinose : Found in sugar beet, cotton and in some fungi. It is made up of glucose, fructose and galactose.

Gentianose : Found in rhizomes of gentian species, made up of glucose and fructose.

(c) Tetrasaccharides : Composed of four molecules of same or different sugars. Stachyose is found in Stachys tubefera. It is made up of two unit of galactose, one unit of glucose and one unit of fructose.

(d) Polysaccharides : General formula is \[{{({{C}_{6}}{{H}_{10}}{{O}_{5}})}_{n}}\] formed by condensation of several molecules (300-1000) of monosaccharides, (Described under " Macromolecules").

(6) Lipids : Term lipid was coined by Bloor (1943). These are esters of fatty acids and alcohol. They are hydrophobic insoluble in water but soluble in benzene, ether and chloroform. Lipids are classified into three groups :

(i) Simple lipids : These are the esters of fatty acids and glycerol. Again they are typed as :

(a) Fats and Oils : (Natural lipids or true fats). These triglycerides of fatty acid and glycerol. Fats which are liquid at room temperature are called oils.

(b) Fatty acids : Obtained by hydrolysis of fats. Formic acid is simplest fatty acid (HCOOH). These are of 2 types :

• Saturated fatty acids : The fatty acids which do not have double bond in between carbon atoms. e.g., butyric acid, palmitic acid, hexanoic acid, etc. They have high melting points and solid at room temperature.
• Unsaturated fatty acids : The fatty acids which have double bonds (D.B.) in carbon atoms. e.g., oleic acid (1 D.B.), linolic acid (2 D.B.), linolenic acid (3 D.B.), arachidmic acid (4 D.B.) one D.B. containing fatty acid is called MUFA, and with more than one D.B. fatty acid is called PUFA. They have lower melting points mostly found in plant fats and liquid at room temperature.

Linoleic acid, linolenic acid, arachidonic acid are essential fatty acid (Evans and Burr 1928). Deficiency of essential fatty acid causes follicular hyper keratosis disease.

(c) Waxes : These are simple lipids composed of one molecule of long chain fatty acid and long chain monohydric alcohol. Waxes have high melting point, insoluble in water. They reduce rate of transpiration by making plant tissue water proof. Wax present in blood called cholestrol.

Bees wax is a common example of wax. It is a combination of palmitic acid and mericyl alcohol \[({{C}_{30}}{{H}_{61}}OH)\]. Candil contains paraffin wax and stearic acid.

(ii) Compound lipids : They contain some additional or element. Group with fatty acid and alcohol on the basis of group they may be of following types :

(a) Phospholipids : It is amphipathic molecule. These contain phosphoric acid. It helps in transport, metabolism, blood clotting and permeability of cell membrane. e.g., Lecithin, cephalin (Soyabean oil).

(b) Glycolipids : These contain nitrogen and carbohydrate beside fatty acids. Generally found in white matter of nervous system. e.g., sesocine frenocin.

(c) Chromolipids : It includes pigmented lipids e.g., carotene.

(d) Aminolipids / Sulpholipids : It contains sulphur and amino acids with fatty acid and glycerol. Cutin and suberin are also compound lipids.

(iii) Derived lipids : These are obtained by hydrolysis of simple and compound lipids. Derived lipids include following components :

(a) Sterols : Lipids without straight chains are called sterols. They are composed of fused hydrocarbon rings and a long hydrocarbon side chain. Best known sterol is cholesterol.

(b) Digitalin : It is prepared from leaves of Foxglove (Digitalis lantana) is a heart stimulant.

(c) Ergosterol : Present in food, found in ergot and yeast.

(d) Coprosterol : It is found in faeces. It is formed as a result of the reduction by bacteria in intestine from the double bond of cholesterol between \[{{C}_{5}}\]and \[{{C}_{6}}.\]

(e) Terpenes : It is essential oil and present mostly in oils of camphor, eucalyptus, lemon and mint. Phytol is a terpenoid alcohol present in Vitamin A, K, E and in pigments like chlorophyll carotenoid.

Functions of lipids

• Oxidation of lipids yields comparatively more energy in the cell than protein and carbohydrates.
• The oil seeds such as groundnut, mustard, coconut store fats to provide nourishment to embryo during germination.
• They function as structural constituent i.e., all the membrane system of the cell are made up of lipoproteins.
• Amphipathic lipids are emulsifier.
• It works as heat insulator and Used in synthesis of hormones.
• Fats provide solubility to vitamins A, D, E, and K.

(7) Amino acids : Amino acids are basic units of protein and made up of C, H, O, N and sometimes S. Amino acids are organic acids with a carboxyl group \[(COOH)\] and one amino group \[(-N{{H}_{2}})\] on the a -carbon atom. Carboxyl group attributes acidic properties and amino group gives basic ones. In solution, they serve as buffers and help to maintain pH. General formula is \[R-CHN{{H}_{2}}.COOH.\]They are 20 in number specified in genetic code and universal in viruses, prokaryotes and eukaryotes. Which take part in protein synthesis.

Amino acids are amphoteric or bipolar ions or Zwitter ions. Amino acids link with each other by peptide bond and long chains are called polypeptide chains. Total known amino acid are more than 200 out of these only 20 amino acid takes part in protein synthesis called protein amino acid.

Classification

(i) Based on R-group of amino acids

Simple amino acids : These have no functional group in the side chain. e.g., glycine, alanine , leucine, valine etc. Glycine is a simplest amino acid.

Hydroxy amino acids : They have alcohol group in side chain. e.g., threonine, serine, etc.

Sulphur containing amino acids : They have sulphur atom in side chain. e.g., methionine, cysteine.

Basic amino acids : They have basic group \[(-N{{H}_{2}})\] in side chain. e.g., lysine, arginine.

Acidic amino acids : They have carboxyl group in side chain. e.g., aspartic acid, glutamic acid.

Acid amide amino acids : These are the derivatives of acidic amino acids. In this group, one of the carboxyl group has been converted to amide \[(-CO.N{{H}_{2}})\]. e.g., asparagine, glutamine.

Heterocyclic amino acids : These are the amino acids in which the side chain includes a ring involving  atleast one atom other than carbon. e.g., tryptophan, histidine.

Aromatic amino acids : They have aromatic group (benzene ring) in the side chain. e.g., phenylalanine, tyrosine, etc.

(ii) On the basis of requirements : On the basis of the synthesis amino acids in body and their requirement, they are categorized as :

Essential amino acids : These are not synthesized in body hence to be provided in diet e.g., valine, leucine, isoleucine, theronine ,lysine, tryptophan, phenylalanine, methionine etc.

Semi-essential amino acids : Synthesized partially in the body but not at the rate to meet the requirement of individual. e.g., arginine and histidine.

Non-essential amino acids : These amino acids are derived from carbon skeleton of lipids and carbohydrate  metabolism. In humans there are 12 non- essential amino acids e.g., alanine, aspartic acid, cysteine, glutamic acid etc. Proline and hydroxyproline have, NH (imino group) instead of \[N{{H}_{2}}\] hence are called imino acids.

(8) Nucleotides : Structurally a nucleotide can be regarded as a phosphoester of a nucleoside. A combination of nitrogenous base and a sugar is called nucleoside and combination of a base, a sugar and phosphate group is known as nucleotide.

\[{{N}_{2}}\]base + Pentose sugar\[\to \] ‘Nucleoside’

Nucleoside + Phosphoric acid\[\to \]‘Nucleotide’ \[+{{H}_{2}}O.\].

There are two types of pentose sugars, ribose found in RNA and deoxyribose found in DNA. There are two types of bases which occur in the nucleic acids.

(i) Purines : Purines are 9 membered double ringed nitrogenous bases which possess nitrogen at 1' ,3' ,7' and 9' positions. They are adenine (A) and guanine (G).

(ii) Pyrimidines : They are smaller molecule than purines. These are 6 membered single ringed nitrogenous bases that contain nitrogen at 1' and 3' positions like cytosine (C), thymine (T) and uracil (U). In DNA adenine pairs with thymine by two \[{{H}_{2}}\] bond and cytosine pairs with guanine by three \[{{H}_{2}}\]bond.

A nucleotide may have one, two or three phosphates, as one in AMP, two in ADP. The II and III phosphate bond is called high energy bond and it release about 8 K cal. ATP was discovered by Karl Lohmann (1929). Formation of ATP is endergonic reaction.

Functions of nucleotides

• Formation of nucleic acids : Different nucleotides polymerize together to form DNA and RNA.
• Formation of energy carrier : They help in formation of ATP,AMP, ADP, GDP, GTP, TDP,TTP, UDP, etc. which on breaking release energy.
• Formation of Coenzymes : Coenzymes like NAD, NADP, FMN, FAD, CoA, etc are formed.