Basic Concept of Biotechnology 23

  Biomolecules   A living system grows, sustains and reproduces itself. The most amazing thing about a living system is that it is composed of non-living atoms and molecules. The pursuit of knowledge of what goes on chemically within a living system falls in the domain of Biochemistry. Even though there are thousands of different types of molecules in a cell, there are only a few basic classes of bimolecular like carbohydrates, proteins, nucleic acids, lipids, etc. Proteins and carbohydrates are essential constituents of our food. In addition, some simple molecules like vitamins and mineral salts also play an important role in the functions of organisms. The complexity of even the simplest of life forms, the single cell, cannot be overstated. Nevertheless, from a chemical perspective, cellular components can be segregated into macromolecules (DNA, RNA, proteins, etc.), relatively simple molecules (amino acids, monosaccharide’s, and lipids), and their precursors: CO 2 ,H 2 O, and NH 3 .

  Carbohydrates Carbohydrates are the most abundant bimolecule belonging to class of organic compounds found in living organisms on earth. Each year, more than 100 billion metric tons of CO 2  and H 2 O are converted into cellulose and other plant products due to photosynthesis. Living matter is largely made of bimolecule consisting of water and complex polymers of amino acids, lipids, nucleotides and carbohydrates. Carbohydrates are most special of them in that they remain associated with the three other polymers mentioned. Carbohydrates are linked with amino acid polymers (proteins) forming glycoprotein’s and with lipids as glycolipids. Carbohydrates are present in DNA and RNA, which are essentially polymers of D-ribose-phosphate and 2-deoxy-D-ribose phosphate to which purines and pyrimidines bases are attached at the C-1 reducing position. Carbohydrates are a widely diverse group of compounds that are ubiquitous in nature. More than 75% of the dry weight of the plant world is carboh

  Classification of Carbohydrates Carbohydrates are classified into three groups depending upon their behavior on hydrolysis.   i. Monosaccharide’s: A polyhydroxy aldehyde or ketone which cannot be hydrolyzed further to a smaller molecule containing these functional groups is known as a monosaccharide. About 20 monosaccharides occur in nature and glucose is the most common amongst them. Monosaccharides are further classified on the basis of the number of carbon atoms and the functional group present in them. If a monosaccharide contains an aldehyde group, it is known as an aldose and if it contains a keto group,it is known as a ketose. The number of carbon atoms present is also included while classifying the compound as is evident from the examples given in Table 1. Glucose occurs freely in nature as well as in the combined form. It is present in sweet fruits and honey. Ripe grapes also contain glucose in large amounts.   ii.  Disaccharides: Carbohydrates which give two monosaccharide

  Structure of Monosaccharide’s Although a large number of monosaccharide’s are found in nature, we will confine our discussion here to four of them only viz. D-glucose, D-fructose, D-ribose and 2-deoxy-D-ribose. D-Glucose (an aldohexose) is the monomer for many other carbohydrates. Alone or in combination, glucose is probably the most abundant organic compound on the earth. D-Fructose (a ketohexose) is a sugar that is found withglucose in honey and fruit juices. D-Ribose (an aldopentose) is found in ribonucleic acids (RNA) while. 2-Deoxy-D-ribose is an important  constituent of the deoxyribonucleic acids (DNA). Here, the prefix 2-Deoxy indicates that it lacks oxygen at carbon no. 2 These monosaccharides generally exist as cyclic compounds in nature. A ring is formed by a reaction between the carbonyl group and one of the hydroxyl groups present in the molecule. Glucose preferentially forms the six member rings which can be in two different isomeric forms called α- and ß-forms (shown b

  Structure of Di-Saccharides and Polysaccharides Disaccharides are formed by the condensation of two monosaccharide molecules. These monosaccharides join together by the loss of a water molecule between one hydroxyl groups on each monosaccharide. Such a linkage, which joins the monosaccharide units together, is called glycoside linkage. If two α-glucose molecules are joined together, the disaccharide maltose is formed Similarly, sucrose (the common sugar) consists of one molecule of glucose and one molecule of fructose joined together. Lactose (or milk sugar) is found in milk and contains one molecule of glucose and one molecule of galactose. If a large number of monosaccharide units are joined together, we get polysaccharides. These are the most common carbohydrates found in nature. They have mainly one of the following two functions- either as food materials or as structural materials. Starch is the main food storage polysaccharide of plants. It is a polymer of α-glucose and consist

  Importance of carbohydrates Carbohydrates are of great importance in biology. The unique reaction, which makes life possible on the Earth, namely the assimilation of the green plants, produces sugar, from which originate, not only all carbohydrates but, directly or indirectly, all other components of living organisms. The carbohydrates are a major source of metabolic energy, both for plants and for animals that depend on plants for food. Aside from the sugars and starch that meet this vital nutritional role, carbohydrates also serve as a structural material (cellulose), a component of the energy transport compound ATP, recognition sites on cell surfaces, and one of three essential components of DNA and RNA. Importance can be considered under following headings;   Metabolic/Nutritional   The important role of carbohydrates, generally, in the metabolism of living organisms, is well known. The biological breakdown of carbohydrates (often spoken of as "combustion") supplies the

  Rare sugars            Rare sugars are defined by the International Society of Rare Sugars (ISRS) as monosaccharide’s and their derivatives that are rare in nature. They are hardly available for research purposes because of their expensiveness. "Izumoring", a structural framework containing all 34 six-carbon monosaccharide’s linked by enzymatic reactions, has been proposed following the discovery of a key enzyme that converts abundantly occurring monosaccharide’s in nature into rare sugars. This has made possible the mass production of rare sugars from inexpensive sugars such as D-glucose or D-fructose. Rare Sugars are mostly used in pharmaceuticals as precursors for a wide variety of carbohydrate-based drugs. These include nucleoside analogues, which are used in antiviral applications such as HIV, HBV and HCV. Another important class of compounds is complex oligosaccharides and olignonucleotides, which may be used as anti-inflammatory or anti-cancer agents, as well as in h

  Nucleic Acids Every generation of each and every species resembles its ancestors in many ways. How are these characteristics transmitted from one generation to the next? It has been observed that nucleus of a living cell is responsible for this transmission of inherent characters, also called heredity. The particles in nucleus of the cell, responsible for heredity, are called chromosomes which are made up of proteins and another type of bimolecular called nucleic acids. These are mainly of two types, thedeoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Since nucleic acids are long chain polymers of nucleotides, so they are also called polynucleotides. Why is a dog a dog and not a cat? Why do some people have blue or brown eyes and not black? From a chemical standpoint, how does the body know what particular type of protein is to be synthesized? How is this information transmitted from one generation to the next? The study of the chemistry of heredity is one of the most fascinat

  Structure of Nucleic Acids        Like all natural molecules, nucleic acids are linear polymeric molecules. They are chain like polymers of thousands of nucleotide units, hence they are also called polynucleotides. A nucleotide consists of three subunits: nitrogen containing heterocyclic aromatic compound (calledbase), a pentose sugar and a molecule of phosphoric acid. So a nucleic acid chain is represented as shown below.       In DNA molecules, the sugar moiety is 2 -deoxyribose, where in RNA molecules it is ribose. In DNA, four bases have been found. They are adenine (A), guanine (G), cytosine (C) and thymine (T). The first three of these bases are found in RNA also but the fourth is uracil (U). The sequence of different nucleotides in DNA is termed as its primary structure. Like proteins, they also have secondary structure. DNA is a double stranded helix. Two nucleic acid chains are wound about each other and held together by hydrogen bonds between pairs of bases. The hydrogen bo

  Watson and Crick’s double helix structure of DNA  Unlike DNA, RNA is a single stranded molecule, which may fold back on itself to form double helix structure by base pairing in a region where base sequences are complimentary. There are three types of RNA molecules which perform different functions. These are named as messenger RNA (m-RNA), ribosomal-RNA(r-RNA) and transfer RNA (t-RNA) Biological Functions of Nucleic Acids A DNA molecule is capable of self duplication during cell divisions. The process starts with the unwinding of the two chains in the parent DNA. As the two strands separate, each can serve as a master copy for the construction of a new partner. This is done by bringing the appropriate nucleotides in place and linking them together. Because the bases must be paired in a specific manner (adenine to thymine and guanine to cytosine), each newly built strand is not identical but complimentary to the old one. Thus when replication is completed, we have two DNA molecules, e

  Tautomerism The nitrogenous bases in nucleosides and nucleotides, with the exception of adenine and adenosine, undergo enol-keto tautomerism. Studies have shown that the predominant species in solution is the keto form. Examples are uracil and guanine. Biological Functions of Nucleic Acids DNA is the chemical basis of heredity and may be regarded as the reserve of genetic information. DNA is exclusively responsible for maintaining the identity of different species of organisms over millions of years. A DNA molecule is capable of self duplication during cell division and identical DNA strands are transferred to daughter cells. Another important function of nucleic acids is the protein synthesis in the cell. Actually, the proteins are synthesised by various RNA molecules in the cell but the message for the synthesis of a particular protein is present in DNA.

  Nucleosides and nucleotides Nucleosides are molecules formed by attaching a nucleobase to a ribose or deoxyribose ring. Examples of these include cytidine (C), uridine (U), adenosine (A), guanosine (G), thymidine (T) and inosine (I). Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides. Both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides. DNA uses the deoxynucleotides C, G, A, and T, while RNA uses the ribonucleotides (which have an extra hydroxyl (OH) group on the pentose ring) C, G, A, and U. Modified bases are fairly common (such as with methyl groups on the base ring), as found in ribosomal RNA or transfer RNAs or for discriminating the new from old strands of DNA after replication. Each nucleotide is made of an acyclic nitrogenous base, a pentose and one to three phosphate groups. They contain carbon, nitrogen, oxygen, hydrogen and

  Proteins   Proteins are the most abundant macromolecules in living cells. The name protein is derived from the Greek word ‘proteios’ meaning ‘of prime importance’. These are high molecular mass complex amino acids. You will study about amino acids in the next section. Proteins are most essential class of biomolecules because they play the most important role in all biological processes. A living system contains thousands of different proteins for its various functions. In our every day food pulses, eggs, meat and milk are rich sources of proteins and are must for a balanced diet. Proteins are molecular tools that perform an astonishing variety of functions. In addition to serving as structural materials in all living organisms (e.g., actin and myosin in animal muscle cells), proteins are involved in such diverse functions as catalysis, metabolic regulation, transport, and defense. Proteins are composed of one or more polypeptides, unbranched polymers of 20 different amino acids. The

  Amino Acids The hydrolysis of each polypeptide yields a set of amino acids, referred to as the molecule’s amino acid composition. The structures of the 20 amino acids that are commonly found in naturally occurring polypeptides. Amino acids are the most versatile small biomolecules. They fulfil a number of extremely important roles in biology. These include: building blocks of proteins which are polymers of amino acids, precursors of hormones, and precursors of molecules with specialized physiological functions, e.g., the neurotransmitter dopamine and the hormone thyroxine are both derivatives of the amino acid tyrosine. As the name implies, amino acids contain amino and carboxyl groups. They can be divided into groups based on acidic, basic, and neutral properties when dissolved in water. They are also classified according to solubility, e.g., hydrophilic and hydrophobic. There are 20 so-called amino acids in proteins; however, one of these, proline, is in fact an imino acid. Ninetee

  Non-proteinogenic amino acids: Amino acids are multifunctional organic compounds that contain at least one amino and one carboxyl group attached to a central carbon atom, whose side chains may vary in length and branching as well as in content of other functional groups or aromatic rings. Amino acids may form numerous molecular structures, where the relative position of the amino and carboxyl function allows their general classification as 2-, 3-, 4- etc. (also referred to as α, β, γ, etc.) amino acids. Most amino acids have at least one asymmetric carbon and are chiral. Amino acids are classified as non-protein when they are not part of the 22 such molecules that are translated into proteins by the standard genetic code. Aside from the twenty standard amino acids and the two special amino acids, there are a vast number of "Non-proteinogenic amino acids (NPA)". Two of these can be encoded in the genetic code, but are rather rare in proteins. Selenocysteine is incorporated i

  Classification of Proteins: Proteins are classified on the basis of their chemical composition, shape and solubility into two major categories as discussed below.   (i)  Simple proteins: Simple proteins are those which, on hydrolysis, give only amino acids. According to their solubility, the simple proteins are further divided into two major groups’ fibrous and globular proteins.   (a)      Fibrous Proteins:  These are water insoluble animal proteins eg.collagen (major protein of connective tissues), elastins (protein of arteries and elastic tissues), keratins (proteins of hair, wool, and nails) are good examples of fibrous proteins. Molecules of fibrous proteins are generally long and thread like.   (b)      Globular Proteins:  These proteins are generally soluble in water,acids, bases or alcohol. Some examples of globular proteins are albumin of eggs, globulin (present in serum), and haemoglobin. Molecules of globular proteins are folded into compact units which are spherical in sh