Define Biochemistry. Who is Father of Biochemistry ?

The science which deals with the study of chemical constituents and the reactions between them in any living organism is called as Biochemistry. Neuberg used biochemistry term for first time and is also known as the “Father of Biochemistry”.

What are Biomolecules?

Biomolecules are defined as any organic molecule present in a living cell which includes carbohydrates, proteins, fats etc. Each biomolecule is essential for body functions and manufactured within the body. They can vary in nature, type, and structure where some may be straight chains, some may be cyclic rings or both. Also, they can vary in physical properties such as water solubility and melting points.

The cells protoplasm has organic as well as inorganic matter which is together called as biomolecules as these chemicals make life possible in a cell.

What are Cellular Biomolecules?

The cellular biomolecules together are also called as cellular pool which includes water, inorganic materials and organic materials. There are various types of divisions of the biomolecules :

Micromolecules & macromolecules : The concentrations, weight, structure and solubilities of molecules in a cell differ for all the types present. The molecules which have low molecular weight, simple structures and higher solubilities are called as micromolecules, E.g. minerals, water, sugars (simple and complex), amino acids. The chemicals that have higher molecular weight, lower solubilities, and complex structures are called as macromolecules, e.g. nucleic acids, proteins.

Organic & inorganic compounds : The molecules that have C, H, O together in their composition is called as organic compounds. E.g. carbohydrates, proteins, fats, nucleic acids. Enzymes, hormones, etc. the molecules that do not have C, H, O as a group in their composition is called as inorganic compounds. E.g. minerals, water.

Major elements & minor elements : The elements that are in higher amounts in a cell is called as major elements. E.g. carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), sulphur (S). They in all make the 98% of protoplasmic weight, thus also termed as protoplasmic elements.

Minor elements are the chemicals that are in less amounts in the cell. E.g. calcium (Ca), magnesium (Mg), potassium (K), chlorine (Cl), iodine (I), iron (Fe), sodium (Na). They make the 2% weight of the protoplasm.

How did Scientist Analysed the Chemical Components of the Cell?

The cell usually is of micrometre size which is enclosed in a membrane or a wall. Thus, to study its constituents we need to open the cell and expose or reveal its compounds.
The cell is hence extracted from a source (plant stem, animal liver, microbial colony, etc.) and then mixed with trichloroacetic acid (Cl₃CCOOH). This mixture is ground with pestle and mortar which is further strained through cheese cloth or cotton.
The resultant has two fractions: filtrate is called as acid soluble pool, while the residue is called as acid insoluble fraction.
The acid pool includes cytoplasmic composition. The cytoplasm and organelles have macromolecules which are insoluble in acid and thus are present in the residue.
The fractions obtained are further separated to identify and study the components of the cell by various analytical techniques.
The conclusions from the methods used are that the cell has both small and large molecules present in it. The filtrate is found to have small molecular weight chemicals called as biomicromolecules and large molecular weight chemicals are called as biomacromolecules.

KNOWLEDGE BUILDER

What is the role of Polysaccharides in Biomolecules ?

The acid insoluble pallet includes polysaccharides (carbohydrates) which is a macromolecule. Polysaccharides have monosaccharides in long chains, called as polymers. They are threads or fibers (literally a cotton thread) which are made up of different monosaccharides, called as building blocks. For example, cellulose which is a polymeric polysaccharide made from only one type of monosaccharide – glucose. Thus, cellulose is a homopolymer. Starch is different from a homopolymer and is as a store for energy source in all the plant tissues. Animals have glycogen which is again a different homopolymer, a storage compound of energy. Inulin is a polymer made up of fructose. A polysaccharide chain has two different ends, the right end is called as the reducing point while the left end is called as the non-reducing point. Starch is a homopolymer which has helical secondary structures. Starch has the ability to capture iodine molecules in the helical portion and turns the solution in blue colour. Cellulose on other hand lack the ability to hold the iodine molecules and thus do not turn the iodine solution blue.

Cellulose is a major constituent of cell wall in almost all the plants. Paper which is made from plant pulp contains mainly cellulose. Cotton fiber also is majorly cellulose only. Not only these polysaccharides, but several more complex structures exist for polysaccharides in nature. They exist as building blocks, amino sugars and chemically modified sugars combined with several other compounds (e.g., glucosamine, N-acetyl galactosamine etc.). Exoskeletons of arthropods, is made up of complex polysaccharide called as chitin which is a heteropolymer.

Write four major classes of Biomolecules

There are four major classes of Biomolecules :

Carbohydrates, Proteins, Nucleic acids and Lipids. Each of them is discussed below.

Explain Carbohydrates, thier types and functions in our body

Carbohydrates are macronutrients and are one of the three main ways by which our body obtains its energy. They are called carbohydrates as they comprise carbon, hydrogen and oxygen at their chemical level.

Carbohydrates are essential nutrients which include sugars, fibers and starches. They are found in grains, vegetables, fruits and in milk and other dairy products. They are the basic food groups which play an important role in a healthy life.

The food containing carbohydrates are converted into glucose or blood sugar during the process of digestion by the digestive system.

Our body utilizes this sugar as a source of energy for the cells, organs and tissues. The extra amount of energy or sugar is stored in our muscles and liver for further requirement. The term ‘carbohydrate’ is derived from a French term ‘hydrate de carbone‘ meaning ‘hydrate of carbon‘. The general formula of this class of organic compounds is C_n(H₂O)_n.

They have Carbon, Hydrogen and Oxygen in a 2:1ratio of the H : O, thus also called as hydrates of carbon.
Generalized formula of carbohydrates is C_x(H₂O)_ywhere x and y are real natural numbers from 1, 2, 3…
There are simple carbohydrates and complex carbohydrates. The simple ones are soluble in water and taste sweet which are called as “Sugar”. The complex ones are insoluble in water and have no taste at all.
The structure of simple carbohydrates has an aldehyde group and complex carbohydrates has ketone group.
Carbohydrates are chemically defined as polyhydroxy aldehydes or ketones or compounds which produce them on hydrolysis.

Classification of Carbohydrates

The saccharide number changes in carbohydrates which forms the basis of classification. Major classes are Monosaccharides, Oligosaccharides and Polysaccharides.

In layman’s terms, we acknowledge carbohydrates as sugars or substances that taste sweet. They are collectively called as saccharides (Greek: sakcharon = sugar). Depending on the number of constituting sugar units obtained upon hydrolysis, they are classified as monosaccharides (1 unit), oligosaccharides (2-10 units) and polysaccharides (more than 10 units). They have multiple functions’ viz. they’re the most abundant dietary source of energy; they are structurally very important for many living organisms as they form a major structural component, e.g. cellulose is an important structural fibre for plants.

Monosaccharides

General Characteristics

They are the simplest sugars which cannot be further
The formula is C_n(H₂O)_n for monosaccharides.
Monosaccharides occur in D and L conformation with the exception of Dihydroxy acetone which does not has chiral carbon in its structure. Chiral carbon is the central carbon which has all its four valences satisfied by different functional groups
The saccharides have either ring or straight chain structure.

**Note : Epimer: Isomer formed after there is interchange in the functional group – OH and – H groups on 2, 3 and 4 carbon atom in glucose structure, are known as Epimer. Example: Epimer of Glucose are Mannose (Difference on C2 carbon) and Galactose (Difference on C4 carbon)

Classification of Monosaccharides on the basis of number of Carbons

Explain different types of Monosaccharides and their applications

Ribulose: Found in nucleoplasm.
Arabinose: Found in Gum Arabic which is obtained from organisms like Acassia Arabia, Acassianilotica, Acassia Senegal. Common use is in cold drinks.
Xylose: Found in cell wall of plants.
Xylusose: Is a component of hemicelluloses in the woods of plants.
Glucose: High amounts in grapes, thus is known as grape sugar. High levels in blood and thus called as blood sugar. Forms main energy source and is respiratory substrate in the cell. The mirror image is also called as dextrose.
Fructose: Has sweetest taste. Present in high amounts in honey and sweet fruits and thus termed as fruit sugar. Thaumatin is sweetest carbohydrate which is extracted from Thaumatococcus danielli bacteria. Aspartame/Aspartin is commonly used as an artificial sweetener in most of the foods. It is non carcinogenic.
Galactose: Brain sugar is it’s another name as it is in high amounts in brain and nervous tissue. This sugar is always a part of some compound (never present in free form). E.g. Hemicellulose, lactose, pectin, glycolipid.
Mannose: Even this sugar is accompanied with some other component and not available in free form. e.g. Albumin – Egg, Hemicellulose – Wood.
Rhamnose: The second carbon atom in the structure lacks one oxygen atom and the molecular formula is C₆H₁₂O₅. The sugar is present in phloem.

What are the derivatives of Monosaccharides ?

Important derivatives of Monosccharides are as follows :

Amino sugars: The hydroxyl group in the second carbon atom is displaced with the amino E.g. Glucosamine, Galactosamine.

Sugar alcohol: The aldehyde group (-CHO) in the sugar is displaced with the primary alcohol (-CH₂OH). E.g. Sorbitol and Mannitol are formed from glucose and mannose, respectively.

Sugar acids: The terminal –CHO or – CH₂OH group of the sugar gets oxidised to produce a carboxyl functional group –COOH. g. Glucoronic acid, galacturonic acid.

Oligosaccharides

General Characteristics

The carbohydrates on hydrolysis give 2 to 10 monosaccharide units (monomers) are called as oligosaccharides.
The monosaccharides have glycosidic bonds that bind them together. The glycosidic bond is formed when the aldehyde or ketone group of one monosaccharide reacts with the alcoholic group of another The structure loses one molecule of H₂O during the glycosidic bond formation (dehydration synthesis).

Explain different types of Oligosaccharides and their applications

Disaccharide

Disaccharide has two monosaccharide units in the structure. E.g. Maltose, Sucrose, Lactose, Trehalose.

All the disaccharides are water soluble and taste sweet, thus are called as
Maltose, commonly known as malt sugar which is an intermediate compound in the starch digestion by enzymes. Maltose has 1- 4 glycosidic linkage between a – D glucose and a – D glucose so maltose is reducing sugar.
Lactose is milk sugar with B-1-4 glycosidic linkage between B-D-glucose and B-D-galactose so lactose is reducing sugar.
Lactose is almost tasteless or very less sweet
Human milk contains maximum lactose which is 7%.
The sugar in plants is transported in the form of sucrose.
Sucrose is called by many names: invert sugar, Cane Sugar or Table Sugar or common sugar or commercial sugar.
Sucrose is made up of a – D-glucose and B – D-fructose units.

The haemolymph of insects has trehalose. There is glycosidic linkage between the two anomeric carbon atoms (a-Glucose and B-Glucose) or 1-1 linkage. Thus, trehalose is a non-reducing sugar.

Structural formulae of some disaccharides are as follows :

Other Oligosaccharides are as :

Trisaccharide: Has three monosaccharide units in the structure. e.g. Raffinose (Galactose + Glucose + Fructose)

Tetrasaccharide: Has four monosaccharide units in the structure. e.g. Stachyose (Galactose + Galactose + Glucose +Fructose)

Pentasaccharide: Has five monosaccharide units in the structure. e.g. Barbascose (Galactose + Galactose + Glucose + Fructose)

Note : Raffinose and Stachyose are present in phloem cells in plants and can also be used for translocation of carbohydrates in phloem.

Polysaccharides

General Characteristics

Polysaccharides are made up of large number of monosaccharide units.
The names end in or suffixed with ‘-an’ so that they are called as glycans.
Pentose polysaccharides are commonly termed as pentosans for g. Araban (from L-arabinose), xylan (from D-xylose), present in cell wall.
Hexose polysaccharides are called as “hexans” for g. mannans (from mannose) cellulose, starch etc. present in plants and animals.
Polysaccharides are non-soluble in water, non-reducing and taste sweet less.
They are classified as nutritive and structural polysaccharides on the basis of their functional group.

Explain different types of Polysaccharides and their applications

Homopolysaccharides: They have same monomers in their structures. The important ones in terms of biology are as follows:

Cellulose

Cellulose is a linear polymer of B-D-glucose units (6000 to 10,000 Dal) which have B 1-4 linkage among the glucose When the cellulose is partially digested it gives a cellobiose unit (Disaccharide).

Cellulose forms major component in a plant cell
Cellulose are 50% in wood and is 90% in cotton.
It is the most abundant molecule for its organic matter on earth.
Urochordates have cellulose like material called as “Tunicin” which is also called as Animal cellulose.
It is used in manufacture of the Rayon fibre (Artificial silk).

Structure of starch grains in various food is shown below :

Starch

Starch is the Storage food or carbohydrates in the plants. Starch is a polymer of a –D-glucose units. Starch consist of two types of chains.

Amylose is an unbranched polymer with 250–300 glucose units joined with a–1,4 linkage
Amylopectin is a branched chain of 30 glucose units that are linked with a–1,4 and a–1,6 linkage bonds.

Amylose with iodine give blue colour while Amylopectin gives red colour.
Starch contains 20% amylose and 80% amylopectin which is present in potato.
Potato starch turns purple or violet in colour when mixed with iodine.

Glycogen

Glycogen: The storage carbohydrate present in animals, maximum amounts are present in liver and muscles. Glycogen is thus also called as animal starch. Glycogen is a highly branched polymer which is made up of alpha –D-glucose.

This carbohydrate has the 1-4 bond linkage at long unbranched chain and 1-6 bond linkage at the branching points in the polymer.
Glycogen turns red colour with iodine solution.
Glycogen is a storage food of many fungi.

Chitin

Chitin is a Linear polymer which consists of N-acetyl- D-glucosamine which is an amino acyl derivative of glucose bonding with B-1-4-linkage.

Chitin forms exoskeleton of animals in Arthropoda phylum and cell walls present in fungi.
It is the second most abundant molecule for organic matter on earth.
It is also called as fungal cellulose as it is in their cell wall.

Inulin

Inulin is a Linear polymer that consist of 25-35 fructose units linked together with B-1-2 bonds.

Inulin is present in Dahlia and Artichoke roots. It is water soluble polysaccharide and it is used to know the glomerular filtration rate.
It is smallest storage polysaccharide.

Dextrin

Dextrin is formed as an intermediate matter during the digestion of glycogen and starch. The hydrolysis of dextrin give glucose and maltose are formed. This is a storage food in yeast and bacteria.

Heteropolysaccharides

Heteropolysaccharides has different monosaccharide units in the structure.
a. Hyaluronic acid: Commonly observed in vitreous humour, umbilical cord, joints and connectivetissue of the animals in the form of a lubricating agent. It is also present in animal cell coat which acts as a binding material (animal cement).

It is made up of D-Glucuronic acid and N-acetyl – D-glucosamine amyl group arranged in alternate orders in the chain. These different monosaccharides have B-1-3 linkage bonds while the disaccharides have B-1-4 linkage bonds.

b. Chondriotin: D- glucuronic acid and N-acetyl galactosamine polymer.

Chondriotin is present in the connective tissue of animals.
Sulphate ester of the chondriotin is a main structural component which is present in the cartilages, tendons and bones of animals.

c. Heparin: It is an anticoagulant of blood. Heparin has D-glucuronic acid and N-sulphate glucosamine molecules arranged in an alternate order in the polymer.
d. Pectins: Methylated galacturonic acid, galactose and arabinose constitute the polymer.

Pectin is found in the plant cell walls where it binds the cellulose fibrils in bundles.
Salts of pectin which is pectates of Ca and Mg form the middle lamella in plants.
Thus, it is also called as plant cement.

e. Hemicellulose: Mannose, Galactose, Arabinose and Xylulose form the structure of the polymer.

Phytalophus have hemicellulose as storage material which is an Ivory palm. This carbohydrate when extracted from this plant, has white, hard and shiny appearance. This is used in manufacture of billiard ball and artificial ivory.

Mucopolysaccharides

The slimy polysaccharides which have the capacity to bind proteins with the water molecules are called as mucopolysaccharides. Mucilage is a common mucopolysaccharide present in plants which are made up of galactose and mannose units.
Similarly hyaluronic acid (in streptococcus, animals sperm), chondriotin, heparin (in blood as anticoagulant) are other common examples.

KNOWLEDGE BUILDER

Lipids

The fats along with its derivatives are called as lipids. The term Lipid was coined by Bloor.

C, H, O are present in all the lipids and the ratio of Hydrogen to Oxygen is never 2:1 like carbohydrates. The oxygen in lipids is very less.
Lipids solubilize in organic solvents like acetones, benzene, chloroform, ether, hot alcohol, etc.
Lipids are found in protoplasm as small globules.
Lipids do not form polymer.
Lipids when oxidized provide double amount of the energy as compared to that of carbohydrates.
The fats or lipids present in the subcutaneous layer is a food reservoir and also a shock–absorber.
Lipid occupies less space during its storage unlike carbohydrate as lipid molecules are hydrophobic and condense in the cell.
Animals store maximum food part in the form of lipids.
Lipid on oxidation are also a source of maximum amount of metabolic water as compared with carbohydrate and protein.

Simple Lipid or Neutral Fats

General Characteristics

These are long chain fatty acids and alcohol esters. In majority of simple lipids, the alcohol is a trihydroxy sugar alcohol i.e. glycerol.

Three molecules of fatty acids are combined with one molecule of glycerol. The bond is called as “ester bond” and the lipids that have such bonds are called as Triglycerides. Three molecules of water are released when triglycerides are formed (dehydration synthesis)

Similar or different fatty acids are present in the composition of a fat molecule. Simple lipids include two fatty acid types.

A phospholipid is composed of two fatty acids, a glycerol unit, a phosphate group and a polar molecule.

Types of Lipids or Fats

Saturated fatty acids – All the carbon atoms in the hydro-carbon chain are saturated or bonded with hydrogen atoms.

Palmitic acid – CH₃(CH₂)₁₄-COOH
Stearic acid – CH₃(CH₂)₁₆-COOH

Unsaturated fatty acids – Some carbon atoms are not valenced with hydrogen atoms or remain unsaturated.

Oleic acid
Linoleic acid
Linolenic acid

Polyunsaturated Lipids

Polyunsaturated fatty acids have more than one double bond in their molecule e.g. Arachidonic acid, Linoleic acid, Linolenic acid, Prostaglandins (derivation of arachidonic acid)

Unsaturated fatty acids are also called as essential fatty acids because these cannot be synthesized in the body.
Simple lipids that have saturated fatty acids are present in solid state at normal room temperature e.g. fats.
Simple lipids that have unsaturated fatty acids in the structure are liquid at room temperatures e.g. oils.
Saturated fatty acids are almost inert or less reactive which tend to get stored in the body and cause obesity.
Unsaturated fatty acids are more reactive and thus are metabolised in the body and provide energy.
Oils with poly unsaturated lipids are best recommendation by physicians to patients suffering from high blood cholesterol or cardio-vascular diseases. This acts in increasing the poly unsaturated fatty acids amounts to saturated fatty acids, without increasing the total fats in the diet. This in all lowers the cholesterol level in blood.

Waxes

Waxes are mono glycerides that have one molecule of fatty acid linked with a mono hydroxy alcohol.

Waxes are an important molecule that protect the cell or tissue in which they are present. They form covering of hair and skin in animals and plants stem, leaves and fruits where waxes do not allow the water to stay on them or solubilize in water.

E.g. Bees Wax (Hexacosyl palmitate)

Carnauba (Myricylcerotate) present on leaves, stem and fruits.

Maximum amount of carnauba covers the leaf surface of the xerophytic plants preventing water loss.

Spermaceti present in the whale and Dolphin skull.

Cerumen or ear wax present in external auditory meatus or opening of ears.

Lanoline or cholesterol ester present in blood, sebum and gonadal ducts where it acts as a lubricating agent.

Conjugated or Compound Lipids

Phospholipids or Phosphatide or Phospholipins

Two fatty acid molecules, glycerol, phosphoric acid (H3PO4) along with nitrogenous compound.

Phospholipids are most common and abundant lipid present in the protoplasm.

They have hydrophilic polar end (H₃PO₄ with nitrogenous compound) as well as hydrophobic non polar end (fatty acids). Such molecules are called as amphipathic. Phospholipids can thus form bimolecular layer in the cell membrane.

Some biologically important phospholipids are as following:

Lecithin or Phosphatidyl choline

Nitrogenous compound is choline in the lecithin.
Lecithin is present in the egg yolk, oil seeds and blood.
The lecithin in blood acts as a carrier molecule to transport other lipids.

Cephalin – The nitrogenous compound is ethanolamine and it is similar to lecithin, present in nervous tissue, egg yolk and blood platelets.

Sphingolipids or sphingomyelins are similar to lecithin however the glycerol is replaced with an amino alcohol sphingosine.

Sphingolipids

They are present in the myelin sheath of nerves, other examples of phospholipid are Phosphatidyl serine, Phosphatidyl inositol, and plasmalogens.

Glycolipid – 2 fatty acid molecules, sphingosine along with the galactose constitute the lipid.

Cerebrosides are present in the white matter of human brain

Gangliosides are present in the nerve ganglia and also spleen. These lipids have N-acetyl neuraminic acid and glucose along with the other compounds.

Glycolipids that are found on the cell surface are helpful in recognition of the cell.

Derived Lipids

These are derived from the simple or conjugated ones and usually have complex structure. These lipids are insoluble in water however solubilize in organic solvents.

Steroids

The molecule has a tetracyclic structure termed as “Cyclopentane perhydrophenanthrene nucleus”. Steroids are divided in two types on the basis of structure :

Sterols: Alcoholic steroids like cholesterol which are abundantly present in the adrenal gland, brain, nervous tissue and also in skin. Cholesterol is a parent steroid from which other biologically important steroids are derived. 7 – Dihydro cholesterol present in the skin is a pro vitamin. When the skin gets exposed to ultraviolet radiation, cholesterol transforms into cholecalciferol commonly called as vitamin D. Cholesterol is also called as the “most decorated micro molecule in biology”. Ergosterol: present in oil seeds, fungi like ergot and yeast. Ergosterol is the precursor for another Vitamin D-Ergocalciferol.
Coprosterol: present in faecal matter produced from the decomposition of cholesterol carried by colon bacteria in intestine. Bile acid- Bile Juice has different steroid acids which help in fat emulsification. E.g. cholic acid, Lithocholic acid etc.
Sterones are Ketonic steroids for E.g. sex hormones in animals. i.e. Male Testosterone and Female Progesterone.
Adreno corticoids: The hormones secreted by adrenal cortex in total are known as adreno corticoid hormone.
Ecdysone hormone is present in insects secreted by prothoracic glands.
Diosgenin is extracted from yam plant (Dioscorea), which is used in the manufacture of antifertility or contraceptive pills.

Chromolipid

It is also called as terpene.
Most complex lipid which is present in the protoplasm.
Chromolipids are made up of repeated isoprene units
E.g.: Carotenoids; vitamin A, E, K; Natural Rubber (Polyterpene)

Proteins

Protein is derived from a Greek word that means “holding first place” (by Berzelius and Mulder)

General Characters of Proteins

C, H, O, N are the essential elements present in the proteins. Many proteins also have sulphur.
In some proteins iodine, iron and phosphorus are also present.
Proteins are second most abundant compounds present in protoplasm. 7%–14% amount of proteins approximately.
Proteins are a polymer of amino acid (Fisher and Hofmeister). There are around 300 amino acids that exist however only 20 types of amino acids are used in making of proteins
All the amino acids are amphoteric in nature as it contains one acidic (–COOH) and an alkaline group (–NH₂).
There are free amino acids present in the protoplasm as ions (at isoelectric point).
Isoelectric point is the pH point at which the amino acids are stable in the electric field.
10 amino acids from total 20 are not synthesized and hence they are obtained from the diet or food.
These depending amino acids are called as essential amino acids. E.g. Threonine, Valine, Lysine,
Phenylalanine Tryptophan, Leucine, Isoleucine, Methionine, Arginine and Histidine where Arginine and Histidine are semi essential.
10 amino acids are synthesized in animal body which are called as non-essential amino acids. For e.g. Glycine, Proline, Alanine, Aspartic acid, Glutamine, Serine, Glutamic acid, Cysteine, Asparagine, Tyrosine.
Eukaryotic proteins have L conformation amino acid while bacteria and antibodies have D-conformation amino acid.
Amino acids are linked with peptide bond to form protein.
Peptidyl transferase enzyme catalyses the synthesis of peptide bond.
Property of protein depends on sequence of amino acid and configuration of protein molecules.

Special Amino acids

Tryptophan : The most complex amino acid which is helpful in the synthesis of I.A.A. (Indole-3-Acetic Acid) a plant growth hormone.
Tyrosine: This helps in the synthesis of the melanin pigment in the skin, Thyroxine hormone, Adrenaline (epinephrine) hormone, and even nor adrenaline (nor epinephrine) hormone.
Proline and hydroxyl proline amino acids have imino group (-NH) is present in place of usual amino (-NH2) group so these two amino acids are also known as imino acid.
Cysteine and methionine have sulphur in their amino acid.
Tyrosine has a polar side group in the amino acid.

Classification of the amino acids on the basis of carboxylic groups and amino groups number.

Acidic amino acid (mono amino di carboxylic amino acid)

There are one amino and two carboxylic groups present in their structure. Net charge is -ve, thus they move towards the anode in electric field. E.g. Glutamic acid, Aspartic acid.

Alkaline amino acid (Di amino mono carboxylic amino acid)

There are two amino and one carboxylic group present in the structure.Net charge = -ve, so they move towards the cathode in electric field. E.g. Histidine, Arginine, Lysine.

Neutral AA (Mono amino mono carboxylic AA)

There are one amino and one carboxylic group present in the structure.
The amino acid as whole has no charge, present in the form of zwitter ions and thus do not move in the electric field.

Configuration of Protein Molecule

Primary Configuration or Structure of Protein

The amino acids that are linked by the peptide bonds are arranged in a straight chain form the primary structure of proteins. The protein structure is newly produced on the ribosomes are primary structure and are highly unstable.

A peptide bond (amide bond) is a covalent chemical bond formed between two amino acid molecules.

Secondary configuration

The protein molecules are spirally coiled in the secondary structure. Now the amino acids are also linked by hydrogen bonds which are formed between the oxygen of one amide group and the hydrogen of another amide group. Proteins are insoluble in water and have fibrous appearance. This structure is of two types:

α-Helix :

Right hand rotation of the spirally coiled chain with approximately (3 +1/2) amino acids present in each turn. There are intramolecular hydrogen bonds between two amino acids of same chain present in the structure e.g. Keratin, Myosin, Tropomyosin.

Keratin is a sclera protein which is fibrous, tough, and resistant in terms of digestion. There is abundance of cysteine amino acid in the structure which gives the hardness to keratin.

β-Helix or β pleated sheath

Protein structure here has zig – zag arrangement. The protein molecules are held together by the intermolecular hydrogen bonding. E.g. Fibroin (in silk).

Tertiary Structure

Proteins in the tertiary structure are highly folded and form a globular appearance. They are water soluble (form colloid solution). This structure has following bonds:

Peptide bonds are the strongest bond present in proteins.
Hydrogen bonds between H and O of the amino acid.
Disulphide bonds: The bond is between S and H group of amino acid (Cysteine) which are the second strongest bond in the protein and stabilize the tertiary structure.
Hydrophobic bonds: The bond between the amino acids that contain the hydrophobic side chains e.g. Aromatic amino acid.
Ionic bond: The formation of the ionic bonds between the two opposite ends of a protein molecule is due to the electrostatic attraction between them.

Majority of the proteins and enzymes present in the protoplasm exhibit tertiary structure.

Quaternary structure

The polypeptide chains that have tertiary structure are linked by different bonds to form the quaternary structure of a protein. There are different polypeptide chains with similar (lactic – dehydrogenase) or dissimilar types (Haemoglobin, insulin).

Quaternary structure is the most stable structure of a protein.