Chapter 5 Biomolecules by Teaching Care online coaching classes

 

Biomolecules –

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 Micromolecules

  • Definition : 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.
  • Elements : They are naturally occuring and they are classified on the basis of their property into metals and non-metals. Again on the basis of presence and requirement in plants and animals, they are grouped into major and minor Which are required in large amount are major bioelements e.g. Ca, P, Na, Mg, S, K, N, etc., while those are required in small amount are called minor bioelements e.g. Fe, Cu, Co, Mn, Mo, Zn, I, etc.

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

  • Framework elements : Carbon, oxygen and
  • Protoplasmic elements : Protein, nucleic acid, lipids, chlorophyll, enzymes,
  • Balancing elements : Ca, Mg and K. counteract the toxic effect of other minerals by ion-balancing. There are 17 essential elements in plants and 24 in 14 elements are non-essential :–

(iv)       Proportion of elements in a cell

 

Oxygen –       O – 62%Chlorine- Cl0.16%
Carbon –      C– 20% major elements (95%)Sulphur – S0.14%
Hydrogen- H– 10%Potassium- K0.11%
Trace elements- 0.75% minor elements (4.25%)Sodium – Na0.10%
Calcium – Ca- 2.5%Magnesium – Mg0.07%
Phosphorous- P- 1.14%Iodine- I0.14%
Iron – Fe0.10%

 

  • Biological compounds : These involve two kinds of
    • Inorganic compounds : Characterised by absence of carbon, simple structure with low molecular weights

e.g. water, minerals, ions and gases etc. Water 80% and inorganic salts 1-3%.

  • Organic compounds : Characterised by presence of carbon bonded to form a straight chain or ring

 

CarbohydratesLipidsProteinsNucleotidesOther compounds
1.0%3.5%12.0%2.0%0.5%

 

  • 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. The aqueous phase may be moleculer solution in which dissolved particles are smaller than 000001 mm and colloidal phase in which particle size varies between 0.0001 – 0.000001 mm. Cellular pool comprises of both crystelloid and colloidal particles. Hence called as crystal colloids the non-aqueous phase comprises of organic molecules present in cell compartments like plasma membrane, mitochondria, chloroplast, etc.

 

  • Water : Liquid of life, major constituent of cell (about 60-90%) and exists in intracellular, intercellular and in 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 High boiling point due to hydrogen bonding. Shows high degree of cohesion and adhesion. It can undergo three states of matter i.e. solid liquid gas. It is dense and heaviest at 4C and solid below it.
  • Carbohydrates : 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

 

  • Composition : It consists of carbon, hydrogen and oxygen in the ratio

Cn H 2n On . It  is also called

 

saccharide and sugars are their basic components. Classification of carbohydrates can be summarised as :–

 

Monosaccharides and their derivatives

Carbohydrates

 

Oligosaccharides (number of monosaccharides from 2 to 10, di, tri, tetrasaccharides etc.)

 

Polysaccharides (number of monosaccharides over 10)

 

Monosaccharides e.g.

Triose – 3C, Tetrose – 4C

Pentose – 5C, Hexose – 6C Heptose – 7C, Octoses – 8C

Nanoses-9C, Decoses – 10C

Derivatives of monosaccharides

Homopolysaccharides (starch, amylopectin, glycogen, cellulose etc.)

Heteropolysaccharides (glycoproteins, starch, proteins)

 

Uric acid e.g. glycouronic acid, galactouronic acid

Aroic acids e.g. glucaroic acid, galactaroic acid

Aminosaccharides e.g. glucosamine, galactosamine

Phosphosaccharides e.g. glucose-6- phosphate, fructose 1,6 biphosphate etc.

Glycosides e.g. nucleotides, nucleosides, Coenzymes etc.

 

Monosaccharides : These are single sugar units which can not be hydrolysed furthur into smaller

 

carbohydrates. General formula is

Cn H 2n On , e.g. Triose-3C, glyceraldehyde, dihydroxyacetone, etc., tetrose,

 

pentose, hexose, etc. About 70 monosaccharides are known, out of which only 20 are present in plants and animals.

(i)         Important Hexoses

 

  • Glucose :

C6 H12 O6 . 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”. Normal level of blood glucose is 80-120mg/100ml. If it exceeds then condition is called “glucosuria”.

  • Fructose : Occurs naturally in fruit juices and Hydrolysis of cane sugar in body also yields fructose.
  • Galactose : It is called as brain It’s an important constituent of glycolipids and glycoproteins.

 

  • Mannose : It is obtained on hydrolysis of plant mannans and It is constituent of albumins, globulins and mucoproteins.

(ii)        Structure of monosaccharides

 

  • Properties of monosaccharide
  • Monosaccharides are colourless, sweet tasting,
  • Due to asymmetric carbon, they exist in different isomeric They can rotate polarized light hence they are dextrorotatory and leavorotatory.
  • D-glucose after reduction gives rise to a mixture of polyhydroxy alcohol, sorbitol or
  • The sugars with a free aldehyde or

 

(iv)       Functions of monosaccharides

Fig : Open chain and ring forms of three hexoses

 

  • Glucose is the ultimate source of ATP in the cell
  • It is used in formation of vitamin
  • The intermediate compounds for the formation of glucose in photosynthesis are triose, tetrose, pentose and heptose,
  • Galactose is a constituent of agar-agar.
  • Glucose is a blood sugar and xylose is a non nutritive
  • Polymerisation of these molecules forms
  • Ribose and deoxyribose are constituent of nucleic acids and nucleotides
  • Glyceraldehyde and dihydroxyacetone are
  • Sugars have free aldehyde or ketone group which can reduce Cu++ to Cu+ and are called reducing sugars. Benedicts or fehling’s test are used to confirm the presence of reducing

 

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 a and b.

a-glycosidic linkage                                         b-glycosidic linkage

 

  • Disaccharides : Composed of two molecules of same or different monosaccharide Also called “double sugars”. Molecular formula is C12 H 22 O11 .
  • Maltose : Also called “malt sugar” stored in germinating seeds of barley, oat, 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
  • Lactose : Milk sugar or 5% in mammalian milk. On hydrolysis yields glucose and galactose. Streptococus lacti converts lactose in to lactic acid and causes souring of
  • Trisaccharides : Composed of three molecules of Molecular formula is C18 H32 O16 .
  • Raffinose : Found in sugar beet, cotton and in some It is made up of glucose, fructose and galactose.
  • Gentianose : Found in rhizomes of gentian species, made up of glucose and
  • Tetrasaccharides : Composed of four molecules of same or different Stachyose is found in

Stachys tubefera. It is made up of two unit of galactose, one unit of glucose and one unit of fructose.

 

  • Polysaccharides : General formula is

(C6 H10 O5 )n formed by condensation of several molecules (300-

 

1000) of monosaccharides, (Described under ” Macromolecules”).

  • Reducing and Non-reducing carbohydrates : Those which reduce Tollen’s reagent or fehling solution are called reducing sugars and those do not reduce are called non-reducing sugars. All monosaccharides and disaccharides except sucrose are While all polysaccharides are non-reducing sugars.
  • Lipids : Term lipid was coined by Bloor. 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:–
  • Simple lipids : These are the esters of fatty acids and Again they are typed as :–
  • Fats and Oils : (Natural lipids or true fats). These triglycerides of fatty acid and Fats which are liquid at room temperature are called oils. Oils with polyunsaturated fatty acids are called polyunsaturated e.g. sunflower oil, lower blood cholesterol.
  • Fatty acids : Obtained by hydrolysis of 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, solid at room temperature and increase blood cholesterol.

Unsaturated fatty acids : The fatty acids which have double bonds in carbon atoms. e.g. 8 hexadecanoic acid, 9 octadecanoic acid etc. They have lower melting points mostly found in plant fats, liquid at room temperature and lower the blood cholesterol.

  • 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, resistant to atmospheric oxidation, chemically inert and not digested by enzymes. They reduce rate of transpiration by making plant tissue water proof and work as excellent

Types of waxes

  • Plant wax : Forms
  • Bee’s wax : It is secretion of abdominal glands of worker It consist of palmitic acid and myricyl alcohol.
  • Lanolin or Wool fat : It is secreted by cutaneous glands, also obtained from wool of It consists of palmitic acid, oleic or stearic acid and cholesterol.
  • Sebum : It is secretion of sebaceous gland of
  • Paraffin wax : Obtained from
  • 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:
  • Phospholipids : These contain phosphoric acid. It helps in transport, metabolism, blood clotting and permeability of cell It is a bipolar molecule i.e. phosphate containing end is hydrophilic whereas fatty acid molecules represent hydrophobic (non-polar tail). Phospholipids again comprises.

Lecithin : These are yellowish grey solids, soluble in ether and alcohol but insoluble in acetone. On hydrolysis they yield glycerol, fatty acid, phosphoric acid and choline. Lecithins are broken down by enzyme lecithinase to lysolecithin. The enzyme is found in venom of bee and cobra.

Cephalins : Found in animal tissue and soyabean oil. Cephalin contains choline or serine sometimes and stearic acid, oleic acid, linoelic and arachidonic acid.

  • Glycolipids : These contain nitrogen and carbohydrate beside fatty acids. Generally found in white matter of nervous e.g. sesocine frenocin.
  • Chromolipids : It includes pigmented lipids g. carotene.
  • Aminolipids : Also known as sulpholipids. It contains sulphur and amino acids with fatty acid and Cutin and suberin are also compound lipids resistant to water and also provide mechanical support in plants.
  • Derived lipids : These are obtained by hydrolysis of simple and compound Derived lipids include following components :–

 

  • Sterols : Lipids without straight chains are called They are composed of fused hydrocarbon rings and a long hydrocarbon side chain. Best known sterol is cholesterol, present in high concentration in nervous tissue and in bile. Cholesterol is also the precursor of hormones like progesterone, testosterone, estradiol and cortisol and vitamin D. Diosgenin is obtained from yam plant (Dioscorea) used in making anti- infertility pills.
  • Digitalin : It is prepared from leaves of Foxglove (Digitalis lantana) is a heart
  • Ergosterol : Present in food, found in ergot and yeast. It is precursor of another form of vitamin D, ergocalciferol ( D2 ).
  • 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 C5 and C6.
  • Tarpens : It is essential oil and present mostly in oils of camphor, eucalyptus, lemon and Phytol is a terpenoid alcohol present in Vitamin A, K, E and in pigments like chlorophyll carotenoid. Other forms are licopene, gibberellins and natural rubber.
  • Prostaglandin : It is hormone like compound derived from arachidonic acid. Mostly present in secretion of seminal vesicles in males and menstrual cycle fluid in
  • Blubber : A very thick layer of subcutaneous fat in

(iv)       Functions of lipids

  • Oxidation of lipids yields comparatively more energy in the cell than protein and 1gm of lipids account for 39.1 KJ.
  • The oil seeds such as groundnut, mustard, coconut store fats to provide nourishment to embryo during
  • They function as structural constituent e. all the membrane system of the cell are made up of lipoproteins.
  • Amphipathic lipids are
  • It works as heat
  • Used in synthesis of
  • Fats provide solubility to vitamins A, D, E, and K.
  • Amino acids : Amino acids are normal components of cell proteins (called amino acid). They are 20 in number specified in genetic code and universal in viruses, prokaryotes and Otherwise amino acids may be termed rare amino acids, which take part in protein synthesis e.g. hydroxyproline and non- protein amino acids do not take part in protein synthesis e.g. Ornithin, citrullin, gama-aminobutyric acid (GABA) a neurotransmitter, etc.
    • Structure and Composition : 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             H

amino group (- NH 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

NH 2C COOH

|

to maintain pH. General formula is

R CHNH 2 .COOH .                                                                     R

 

Amino acids are amphoteric or bipolar ions or Zueitter ions. Amino acids link with each other by peptide bond and long chains are called polypeptide chains.

 

(ii)        Classification

Based on Rgroup of amino acids.

  • Simple amino acids : These have no functional group in the side e.g. glycine, alanine , leucine, valine etc.
  • Hydroxy amino acids : They have alcohol group in side e.g. threonine, serine, etc.
  • Sulphur containing amino acids : They have sulphur atom in side e.g. methionine, cystenine.
  • Basic amino acids : They have basic group (- NH 2 ) in side e.g. lysine, arginine.
  • Acidic amino acids : They have carboxyl group in side chain. 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.NH 2 ) . g. asparagine, glutamine.
  • Heterocyclic amino acids : These are the amino acids in which the side chain includes a ring involving at least one atom other than e.g. tryptophan, histidine.
  • Aromatic amino acids : They have aromatic group (benzene ring) in the side chain. g. phenylalanine, tyrosine, etc.

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 g. valine, leucine, isoleucine, theronine ,lysine, etc.
  • Semi-essential amino acids : Synthesized partially in the body but not at the rate to meet the requirement of e.g., arginine and histidine.
  • Non-essential amino acids : These amino acids are derived from carbon skeleton of lipids and carbohydrate 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

NH 2

hence are called imino

 

acids. Tyrosine can be converted into hormone thyroxine and adrenaline and skin pigment melanin. Glycine is necessory for production of heme. Tryptophan is the precursor of vitamin nicotinamide and auxins. If amino group is removed from amino acid it can form glucose and if COOH group is removed, it forms amines e.g. histamine.

(iii)      Functions of amino acids

  • Amino acids are building blocks of proteins and
  • By glycogenolysis, they form
  • Hormones like adrenaline and thyroxine are formed with the help of
  • Antibiotics often contain non-protein amino
  • They are precursour of many

 

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

 

Types of nitrogen baseNucleosideNucleotide
AdenineAdenosineAdenylic acid
GuanineGuanosineGuanylic acid
CytosineCytidineCytidilic acid
ThymineThymidineThymidylic acid
UracilUridineUridylic acid

 

There are two types of pentose sugars, ribose found in RNA and deoxyribose found in DNA. Nucleotides form 2% of the cell component.

N2 base + Pentose sugar ® ‘Nucleoside’

Nucleoside + Phosphoric acid ® ‘Nucleotide’ + H 2O .

There are two types of bases which occur in the nucleic acids.

  • Purines : Purines are 9 membered double ringed nitrogenous bases which possess nitrogen at 1′ ,3′ ,7′ and 9′ They are adenine (A) and guanine (G).
  • 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 (adenosine monophosphate), two in ADP (adenosine diphosphate). The 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 reaciton.

  • Functions of nucleotides : Following are the major functions of
  • 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, which on

Adenine                Ribose

 

(iv)       Some important Coenzymes

  • NAD+ (Nicotinamide adenine dinucleotide) or Code

Fig : Structure of ATP molecule A-Diagrammatic, B-Molecular

 

hydrogenase-I is involved in many hydrogen transferring reaction. It is Coenzyme I (Vit B5).

 

  • Coenzyme II or Code hydrogenase II or NADP+ ; TPN (triphopyridine) etc. it is similar in functioning to Coenzyme-I.
  • Coenzyme A : It is a complex thiol derivative unlike Co-I and Co-II, Co-A is not a oxidising- reducing Coenzyme but is acylating e. Co-A accepts acetyl groups from one metabolite and denotes them to another in the presence of specific enzymes. Most important Co-A compound is acetyl Co-A (activated acetate). Beside acylation Coenzyme-A can also undergo phosphorylation.
  • Flavonucleotides : FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide) take part in oxidation reaction and also function as FMN is vitamin B2 or riboflavin.

(v)Important points

  • On the basis of presence of aldehyde or ketone groups glyceraldehyde may be termed as an aldotriose and dihydroxyacetone is then called
  • General formula of oligosaccharide is Cn (H 2 O)n-1 .
  • Isomaltose has a-1-6
  • Musein is a
  • Cobalt is constituent of B12 and required for synthesis of phytochromes and auxins.
  • Copper is a constituent of plastocyanine and co-factor of respiratory
  • Boron is necessory for plants in sugar
  • Galactose is a constituent of ‘gum arabic’.
  • Sweetest protein is
  • Lipidosis in born or acquired characteristic syndrome due to lipid
  • Cellulose nitrite is used in propellant
  • Nickle is required for activity of

 Macromolecules .

Macromolecules are polymerisation product of micromolecuels, have high molecular weight and low solubility.

They include mainly polysaccharide, protein and nucleic acids.

Polysaccharide : They are branched or unbranched polymers of monosaccharides jointed by glycosidic bond. Their general formula is (C6 H10 O5 )n . They are also called glycans polysaccharides are amorphous, tasteless and insoluble or only slightly soluble in water and can be easily hydrolysed to monosaccharide units.

(1) Types of polysaccharides On the basis of structure

  • Homopolysaccharides : These are made by polymerisation of single kind of e.g. starch, cellulose, glycogen, etc.
  • Heteropolysaccharide : These are made by condensation of two or more kinds of

e.g. chitin, pectin, etc.

On the basis of functions

  • Food storage polysaccharides : They serve as reserve e.g. starch and glycogen.

 

  • Structural polysaccharides : These take part in structural framework of cell wall g. chitin and cellulose.

(2) Description of some polysaccharides

  • Glycogen : It is a branched polymer of glucose and contain 30,000 glucose It is also called animal

 

starch. Their general formula is

(C6 H10 O5 )n . It is also found as storage product in blue green algae, slime moulds,

 

fungi and bacteria. It is a non-reducing sugar and gives red colour with iodine. In glycogen, glucose molecule are linked by 1 – 4 glycosidic linkage in straight part and 1 – 6 linkage in the branching part glycogen has branch points about every 8-10 glucose units.

a – 1 – 4 linkage

  • Starch : Starch is formed in photosynthesis and function as energy storing Generally found in the form of grains, which contain 20% water. It is found abundantly in rice, wheat, legumes, potato (oval and ecentric shaped), banana, etc. Starch is of two types. Straight chain polysaccharides known as amylose and

 

branched chain as amylopectin. Both composed of D – glucose units jointed by

a – 1 – 4

linkage and

a – 1 – 6

 

linkage. It is insoluble in water and gives blue colour when treated with iodine. Amylose consists of 200 – 500

glucose units. It is stored inside chloroplast or spherical leucoplast and known as amyloplasts.

  • Inulin : Also called “dahlia starch”(found in roots). It has unbranched chain of 30 – 35 fructose units

 

linked by

b – 2 – 1 glycosidic linkage between 1 and 2 of carbon atom of D – fructose unit.

 

  • Cellulose : An important constituent of cell wall (20 – 40%), made up of unbranched chain of 6000 b–D glucose units linked by 1 – 4 glycosidic linkage. It is fibrous, rigid and insoluble in water. Wood (20 – 50%) and cotton (90%) contain large amount of Rayon (artificial fibre) cellulose, nitrate (used as explosive) and carboxyl methyl cellulose (used as cosmetics and ice cream) are obtained by activity of “cellulase” enzyme. It doesn’t give any colour when treated with iodine.

 

  • Chitin : It is a polyglycol consisting of N-acetyl–D–glucosamine units connected with

b – 1, 4

glycosidic

 

linkage. Mostly it is found in hard exoskeleton of insects and crustaceans and some times in fungal cell wall. Second most abundant carbohydrate.

  • Agar-Agar : It is a galactan, consisting of both D and L galactose and it is used to prepare bacterial It is also used as luxative and obtained from cell wall of red algae e.g. Gracilaria, Gelidium, etc.
  • Pectin : It is a cell wall material in collenchyma tissue may also be found in fruit pulps, rind of citrus fruits It is water soluble and can undergo sol gel transformation. It contain arabinose, galactose and galacturonic acid.
  • Neutral sugars : It is found associated with cellulose in cell The common sugars in hemicellulose are D-xylose, L–arabinose, D-galactose, D-mannose and D-glucusonic acid. e.g. hemicellulose.
  • Gum : It secreted by higher plants after injury or pathogenic It is viscous and seals the wound. It involves sugars like L-arabinose, D-galactose, D-glucusonic acid. e.g. gum arabic.

 

  • Mucopolysaccharides : These are gelatinous substance, containing amino sugars, uronic acid, etc. All slimy substances of plant are mucopolysaccharide. g. hyaluronic acid, vitreous humour, chondridine sulphate, heparin, husk of isabgul and mucilage of also.
  • Glycoproteins : They include some plasmaprotein and blood group substances. They doesn’t contain uronic
  • Murein : It is a peptidoglycan, linked to short chains of It is constituent of cell wall of bacteria and blue green algae.

(3) Properties of polysaccharides

  • They are tasteless and colourless
  • Insoluble in water, soluble in alcohol and more soluble in
  • Can be easily hydrolyzed into their
  • Their molecular weight is high.
  • They do not diffuse through plasma

(4) Functions

  • Cellulose pectin and chitin are constituents in cell wall of higher plants but peptidoglycan in the cell wall of
  • They are reserve food
  • They form protective
  • They can be used as culture
  • Being insoluble they do no exert osmotic or chemical influence in the
  • Fibres are obtained used in making cloth and
  • Nitrocellulose and trinitrate cellulose (gun-cotton) used as

 

Protein : The word protein was coined by Berzelius in 1838 and was used by G. J. Mulder first time 1840. 15% of protoplasm is made up of protein. Average proteins contain 16% nitrogen, 50–55% carbon, oxygen 20–24%, hydrogen 7% and sulphur 0.3 – 0.5%. Iron, phosphorous, copper, calcium, and iodine are also present in small quantity.

Peptide linkage.

 

  • Structure of proteins : It is due to different rearrangement of amino When carboxyl group

(-COOH) of one amino acid binded with amino group (– NH2) of another amino acid the bond is called peptide

bond. A peptide may be dipeptide, tripeptide and polypeptide. The simplest protein is Insulin. According to Sanger

(1953) insulin consists 51 amino acids. A protein can have up to four level of conformation.

  • Primary structure : The primary structure is the covalent connections of a protein. It refers to linear sequence, number and nature of amino acids bonded together with peptide bonds e.g. ribonuclease, insulin, haemoglobin, etc.

 

  • Secondary structure : The folding of a linear polypeptide chain into specific coiled structure (a – helix) is

called secondary structure and if it is with intermolecular hydrogen bonds the structure is known as b – pleated

 

sheet.

a – helical structure is found in protein of fur, keratin of hair claws, and feathers.

b – pleated structure is

 

found in silk fibres.

  • Tertiary structure : The arrangement and interconnection of proteins into specific loops and bends is called tertiary structure of proteins. It is stabilized by hydrogen bond, ionic bond, hydrophobic bond and disulphide It is found in myoglobin (globular proteins).
  • Quaternary structure : It is shown by protein containing more than one peptide chain. The protein consists of identical units. It is known as homologous quaternary structure e.g. lactic dehydrogenase. If the units are dissimilar, it is called as heterogeneous quaternary structure g. hemoglobin which consists of two a – chains and

 

two

b – chains.

  • Classification of proteins : Proteins are classified on the basis of their shape, constitution and

On the basis of shape

  • Fibrous protein/Scleroprotein : Insoluble in Animal protein resistant to proteolytic enzyme is

 

spirally coiled thread like structure form fibres. e.g. collagen (in connective tissue), actin and myosin, keratin in hairs, claws, feathers, etc.

  • Globular proteins : Soluble in Polypeptides coiled about themselves to form oval or spherical molecules e.g. albumin insulin hormones like ACTH, oxytosin, etc.

On the basis of constituents

  • Simple proteins : The proteins which are made up of amino acids e.g. albumins, globulins, prolamins, glutelins, histones, etc.
  • Conjugated proteins : These are complex proteins combined with characterstic non–amino acid substance called as prosthetic These are of following types :–
  • Nucleoproteins : Combination of protein and nucleic acids, found in chromosomes and e.g.

deoxyribonucleoproteins, ribonucleoproteins, etc.

  • Mucoproteins : These are combined with large amount (more than 4%) of carbohydrates g. mucin.
  • Glycoproteins : In this, carbohydrate content is less (about 2 – 3%) g. immunoglobulins or antibiotics.
  • Chromoproteins : These are compounds of protein and coloured e.g. haemoglobin, cytochrome, etc.
  • Lipoproteins : These are water soluble proteins and contain e.g. cholesterol and serum lipoproteins.
  • Metalloprotein : These are metal binding proteins, AB1–globin known as transferring is capable of combining with iron, zinc and copper g. chlorophyll.
  • Phosphoprotein : They composed of protein and phosphate g. casein (milk) and vitellin (egg).
  • Derived proteins : When proteins are hydrolysed by acids, alkalies or enzymes, the degredation products obtained from them are called derived proteins. On the basis of progressive cleavage, derived proteins are classified as primary proteoses, secondary proteoses, peptones, polypeptides, amino acids,

 

On the basis of nature of molecules

  • Acidic proteins : They exist as anion and include acidic amino e.g. blood groups.
  • Basic proteins : They exist as cations and rich in basic amino acids g. lysine, arginine etc.

(3) Function of Proteins

  • Proteins occur as food reserves as glutelin, globulin casein in
  • Proteins are coagulated in solutions, alkaline to the isoelectric pH by positive ions such as

Zn 2+ , Cd 2+ , Hg 2+ etc. Casein – pH 4.6, cyt. C – 9.8, resum globulin 5.4, pepsin 2.7, lysozyme 11.0 etc.

 

  • Proteins are the most diverse molecule on the
  • Proteins work as hormone as insulin and
  • Antibiotics as gramicidin, tyrocidin and penicillin are peptides.
  • They are structural component of
  • They are biological
  • Monellin is the sweetest substance obtained from African berry (2000 time sweeter than sucrose).
  • Proteins helps in defence, movement activity of muscles, visual pigments receptor molecules,
  • Natural silk is a polyamide and artificial silk is a Nitrogen is the basic constituent.

  Nucleic acid .

  • Definition : Nucleic acids are the polymers of nucleotide made up of carbon, hydrogen, oxygen, nitrogen and phosphorus and which controls the basic functions of the cell. These were first reported by Friedrich Miescher (1871) from the nucleus of pus cell. Altmann called it first time as nucleic acid. They are found in nucleus. They help in transfer of genetic information.
  • Types of nucleic acids : On the basis of nucleotides e. sugars, phosphates and nitrogenous bases, nucleic acids are of two types which are further subdivided. These are DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid).

DNA (Deoxyribonucleic acids)

  • Types of DNA : It may be linear or circular in eukaryotes and prokaryotes
  • Palindromic DNA : The DNA helical bears nucleotide in a serial arrangement but opposite in two

TTAA C G T T A A…….

A A T T G C A A T T……

  • Repetitive DNA : This type of arrangement is found near centromere of chromosome and is inert in RNA The sequence of nitrogenous bases is repeated several times.
  • Satellite DNA : It may have base pairs up to 11 – 60bp and are repetitive in They are used in DNA matching or finger printing (Jefferey). In eukaryotes, DNA is deutrorotatory and sugars have pyranose configuration.
  • Chargaff’s rule : Quantitatively the ratio of adenine (A) to thymine (T) and guanine (G) to cytosine (C) is i.e. “Purines are always equal to pyrimidine”.

 

  • C value : It is the total amount of DNA in a genome or haploid set of
  • Sense and Antisense strand : Out of two DNA strand one which carries genetic information in its cistrons is called sense strand while the other strand does not carry genetic information, therefore, doesn’t produce The non-functional DNA strand is called antisense strand.
  • Heteroduplex DNA : Hybrid DNA formed as a result of recombination is called heteroduplex DNA. It contains mismatched base pair of heterologous base
  • X-Ray crystallography study of DNA : It was done by It shows that the two polynucleotide chains of DNA show helical configuration.
  • Single stranded DNA (ssDNA) : It is single helixed And isolated from bacteriophage f ´ 174 by Sinsheimer (1959). It does not follow chargaff’s rule. The replicative form (RF) has plus – minus DNA helix. e.g. parvovirus.
  • Double helical model of DNA : It is also known as Watson and Crick

RNA or Ribonucleic acid : RNA is second type of nucleic acid which is found in nucleus as well as in cytoplasm i.e. mitochondria, plastids, ribosomes etc. They carry the genetic information in some viruses. They are widely distributed in the cell.

Important Tips

  • ds DNA : All eukaryotes, bacteria, polyoma virus and small pox
  • ss DNA : Bacteriophage f ×174 and
  • ds RNA : Reogroup of viruses, wound tumour
  • ss RNA : TMV, TNV
  • Single genome : virus, bacteria, F2 and R17.
  • Segmented genome : Orthomyxovirus (influenza virus).
  • Natural silk is a polyamide and have nitrogen in high
  • Cairns noticed process of replication of DNA in bacteria and said to be “theta mode”.
  • Ochoa (1967) synthesized RNA in vitro.
  • Actinomycin D prevents
  • Genomic RNA was discovered by Franklin and Conrat (1957).
  • DNA end with no unpaired base is called blunt
  • Portion of DNA that codes for the final mRNA is
  • Pribnow box : The sequence of boxes that orient RNA polymerase so that synthesis proceeds left to
  • Hogness box : (TATA box). The hypothesized eukaryotic RNA polymerase II Analogous to the pribnow box.
  • Nick – A single strand scission of the
  • Bacteriophage T2 infects coli (bacteria).
  • Width of DNA helix is 2nm (20 Å).
  • DNA polymerase-III makes mistake about every 1 in 104 bases and joins an incorrect deoxyribonucleotide to growing
  • The two dimensional structure of tRNA is clover leaf like, but three dimensional form is L-shaped.
  • Initiation of polypeptide chain is done by
  • Term DNA was given by Zacharis.
  • The mitochondria DNA differs from nuclear DNA because of lacking binding

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