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Introduction |
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Biomolecules are complex organic molecules. These molecules form the basic structural constituent of a living cell. The organic compounds such as amino acids, nucleotides and monosaccharides serve as building blocks of complex biomolecules. The important biomolecules are proteins, carbohydrates and fats, enzymes, vitamins, hormones and nucleic acids. Some of the biomolecules are polymers. For e.g., starch, proteins, nucleic acids are condensation polymers of simple sugars, amino acids and nucleotides respectively. |
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The Cell |
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The cell is the fundamental structural and functional unit of living organisms. Cells need energy for active transport, to move molecules between the environment and the cells across cells or within cells. Cells obtain energy by oxidation of molecules like glucose. This oxidation takes place in a complex and controlled way by means of enzymes which are biocatalysts. |
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Photosynthesis and Energy |
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Energy for life processes basically comes from the sun. During photosynthesis, green plants absorb energy from the sun to make glucose and oxygen from carbon dioxide and water. |
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Carbohydrates - Introduction |
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Carbohydrates are the organic molecules that are composed of elements carbon, hydrogen and oxygen. These carbohydrates are referred to as saccharides. Carbohydrates are defined as polyhydroxy-aldehydes or polyhydroxy ketones or compounds, which produce them on hydrolysis. They supply energy and serve as structural constituents. |
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Classification |
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Carbohydrates are classified into three groups based on the number of sugar units and upon their behaviour towards hydrolysis. They are
* Monosaccharides
* Oligosaccharides and
* Polysaccharides. |
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Monosaccharides |
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These are the simple carbohydrates that cannot be hydrolysed to simpler compounds. They are sweet to taste, crystalline and soluble in water. They are commonly known as sugars. They are further classified based on the functional group and number of carbon atoms. They are aldoses and ketoses. |
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Monosaccharide - Glucose |
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Glucose occurs in nature in free as well as combined form. It is present in sweet fruits and honey. Ripe grapes contain ~ 20% of glucose. |
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Anomeric Carbon |
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A pair of stereoisomers that differ in configurations around C-1 are called anomers and the C-1 carbon is called anomeric carbon. The a and b - cyclic forms of D-glucose are known as anomers. In this case, a-anomers of glucose contains the -OH group towards right at C-1 position and b-anomer of glucose contains the -OH group towards left at C-1 position. So, D-glucose exists in two stereo isomeric forms with different specific rotations and melting points. |
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Sucrose |
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Sucrose is made up of a-D-Glucose and b-D-fructose held together by a glycosidic bond, between C1 of a-glucose and C2 of b-fructose. The reducing groups of glucose and fructose are involved in glycosidic bond, so it is a non-reducing sugar. |
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Maltose |
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Maltose is made up of two a-D-glucose (in pyranose form) units held together by a(1 4) glycosidic bond. As there is a free aldehyde group at C-1 position of the second glucose molecule, maltose is known as reducing sugar. Maltose forms osazones. The enzyme that hydrolyses maltose is maltase. |
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Lactose |
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Lactose is made up of b-D-galactose and b-D-glucose held together by b(1 4) glycosidic bond. As the aldehyde group at C-1 position of glucose is free, lactose is known as reducing sugar. Lactose forms osazones. |
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Polysaccharides - Introduction |
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They consist of repeat units of monosaccharides or their derivatives. These units are held by glycosidic bonds. These carbohydrates liberate large number of monosaccharide molecules on hydrolysis. They are colorless and tasteless. So, they are called non-sugars. They are concerned with two important functions - structural and storage of energy. Some examples of polysaccharides are starch, cellulose, glycogen and dextrins. However starch and cellulose are the most important of these. |
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Classification |
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Mucopolysaccharides are the heteroglycans made of repeating units of sugar derivatives like amino sugars and uronic acids. These are known as glycosamino glycans (GAG). Important mucopolysaccharides are hyaluronic acid, chondroitin sulphate and heparin. |
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Structures of Starch and Cellulose |
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Starch occurs in all plants, particularly in their seeds. The main sources are wheat, maize, rice, potatoes, barley and sorghum. |
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Functions of Carbohydrates |
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Carbohydrates participate in a wide range of functions:
* Carbohydrates are most abundant dietary source of energy for all organisms.
* They supply energy and serve as storage form of energy.
* Carbohydrates such as glucose, fructose, starch, glycogen, etc. provide energy for functioning of living organisms. |
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Proteins - Introduction |
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Proteins are the high molecular mass complex biopolymers of amino acids and organic compounds that are most important to life. They are essential for growth and maintenance of life. They are high molecular weight, nitrogen rich substances that are present all living cells of animals and plants. They occur in every part of the cell. They are composed of 20 amino acids, which are repeatedly found in the structure of proteins. These amino acids are liberated when proteins are hydrolyzed. Proteins are the polymers of -amino acids. |
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Structures of Amino Acids |
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Amino acids are the building blocks of proteins. There are 300 amino acids that occur in nature. Among these only 20 are known as standard amino acids that commonly occur in proteins. Amino acids contain two functional groups. They are - amino and carboxyl groups. The amino group (-NH2) is basic and the carboxyl group (-COOH) is acidic in nature. |
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Nomenclature of Amino Acids |
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All amino acids have trivial names. IUPAC names which even if not cumbersome are not used. For e.g., H2N CH2COOH is better known as glycine rather then a-amino acetic acid or 2-amino ethanoic acid. |
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Classification of Amino Acids Base on Polarity |
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Amino acids are classified into different ways based on polarity, structure, nutritional requirement, metabolic fate, etc. Generally used classification is based on polarity. |
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Classification of Amino Acids Based on Nutrition |
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The amino acids that are to be supplied through diet are called as essential amino acids. They cannot be produced by the body. The essential amino acids are arginine, valine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine and tryptophan. |
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Physical Properties of a-Amino Acids |
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Amino acids are colourless, crystalline solids. They are water-soluble high melting solids and behave like salts. The a-carbon atom has 'R' which is a side chain. This side chain is different for different amino acids. The carboxyl and amino groups interact resulting in the transfer of proton from carboxyl group to amino group. Thus the amino acid exists in ionised form known as zwitter ion. This explains the physical properties of these a-amino acids. |
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Iso-electric Point |
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It is defined as the point at which a molecule exists as zwitter ion with no net charge. Thus, at this point the molecule is electrically neutral. The molecules have minimum solubility, maximum precipitability and least buffer capacity. The acidic amino acids and basic amino acids strongly influence the iso-electric point (PI). The PI value of protein is determined by the nature of ionizable groups of amino acids. By taking average Pka values of ionisable groups PI value can be calculated. |
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Chemical properties of a-amino acids |
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When two amino acids combine with each other, the amino group of one amino acid combines with carboxyl group of other amino acid. This leads to peptide bond formation. The combination of the amino group of one molecule with the carboxyl group of the other results in the elimination of a water molecule and forms a -CO-NH-bond. |
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Poly Peptides |
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Peptides containing more than 10 amino acids are called poly peptides. Poly peptides are formed by the linear sequence of amino acids. Some proteins are composed of two or more poly peptide chains. Relatively shorter peptides are known as oligopeptides whereas longer polymers are called polypeptides. Polypeptides containing more than 100 amino acids having molecular mass higher then 10,000 are generally called as proteins. However the distinctive between a polypeptide and a protein is not sharp. |
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Structure of Proteins Primary Structure |
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Proteins are biopolymers containing a large number of amino acids joined to each other by peptide linkages having three dimensional structures. |
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Structure of Proteins - Secondary Structure |
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This structure explains the folding of a polypeptide chain. Two different types of secondary structures are observed. |
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Structure of Proteins - Tertiary structure |
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The three dimensional structure of a protein is known as tertiary structure of a protein. This is a compact structure i.e., further folding of the secondary structure. It coils and folds in such a way that the hydrophobic side chains are held interior and the hydrophilic groups are held outside. This arrangement gives stability to the molecule. The tertiary structure is maintained by hydrogen bonds, disulfide bonds, ionic bonds and hydrophobic interactions. This structure brings distant amino acid side chains nearer. |
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Denaturation of Proteins |
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Denaturation is a process by which the native form of protein structure is disorganized. This causes drastic changes in a protein molecule. Denaturation is caused by some physical and chemical agents. Denaturation causes loss in biological activity of protein. The peptide bonds in the primary structure are not hydrolyzed, but helical structure of the protein is lost. Protein is soluble in water but after denaturation it is insoluble and easily digested. |
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Biological function of proteins |
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Proteins are primarily responsible for the structure and strength of the body. |
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Enzymes |
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Enzymes are the biocatalysts of life. They are defined as biocatalysts synthesized by living cells. They are simple or conjugate protein and specific in action. At present about 300 enzymes are recognized and classified into six classes by International Union of Biochemistry (IUB). They are: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases and Ligases. However about ~10% i.e., 300 enzymes are commercially available. |
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Nucleic Acids - Introduction |
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Nucleic acids are the long chain bio-polymers with complex structure. They serve as transmitters of genetic information. There are two types of nucleic acids they are Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Nucleic acids are built up by monomeric units called nucleotides. They contain a polyphosphate ester chain. |
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Structures of purines and pyrimidines |
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(have a fused ring) (have a single hetero cyclic ring) |
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Structure of Nucleotides and Nucleosides |
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Nucleotide consists of a base, sugar and phosphate. Nucleoside consists only base and sugar. Thus, the structure of nucleotide can be said as nucleoside + phosphate. |
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Nucleic Acids - DNA |
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Nucleic acids are of two types. They are DNA and RNA. In higher cells, DNA is localised mainly in the nucleus within the chromosome. A small amount of DNA is present in the cytoplasm also it is contained in the mitochondria and chloroplasts. |
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Nucleic Acids - RNA |
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RNA molecule is a single stranded structure made of ribonueleotides. RNA contains the pyrimidine uracil instead of thymine in DNA. RNA is of 3 types, based on the cellular composition. |
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Synthesis of proteins - Transcription and Translation |
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This is a process in which RNA is synthesized from DNA. Among the two strands of DNA one strand serves as template and is called as coding strand where as the other strand is called as non-coding strand as it does not participate in transcription. Transcription involves three different stages. |
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Genetic Code |
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Genetic code is the dictionary of nucleotide bases, which determines the sequence of amino acids in proteins. The genetic code (or) codons have triplet base sequences in m RNA, which act as code words for amino acids. The DNA sequence that code for a specific protein(or) polypeptide is called a gene. There are 4 different bases in m RNA - A, G, C and U. They produce 64 different triplets (43). Out of 64 codons 61 codons code for 20 amino acids. The 3 codons UAA, UAG and UGA do not code for amino acids and they are called non-sense codons. The codons AUG and GUG are called initiating codons. |
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Mutation |
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Mutation is defined as a chemical change in the DNA structure of a gene. A difference of a single base in the DNA molecule or a single error in the reading of the code can cause a change in the amino acid sequence which leads to mutation. |
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Lipids |
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Lipids are organic substances present in all living organisms. They include fats, oils, waxes and other related compounds. They are insoluble in water and hydrophobic, and soluble in organic solvents. They are related to fatty acids and are not polymers. They are esters of long chain fatty acids and alcohols. |
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Hormones |
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Hormones are the chemical messengers of the body. They are defined as organic substances secreted into blood stream to control the metabolic and biological activities. These hormones are involved in transmission of information from one tissue to another and from cell to cell. These substances are produced in small amounts by various endocrine (ductless) glands in the body. They are delivered directly to the blood in minute quantities and are carried by the blood to various target organs where these exert physiological effect and control metabolic activities. Thus frequently their site of action is away from their origin. Hormonesare required in trace amounts and are highly specific in their functions. The deficiency of any hormones leads to a particular disease, which can be cured by administration of that hormone. |
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Introduction |
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Vitamins are the organic compounds required for the normal maintenance and health of an organism in minute quantities and their absence cause specific deficiency diseases. These are required in diet in order to perform specific biological functions. There are about 15 vitamins essential for humans. Plants can synthesize cell vitamins whereas only a few are synthesized in animals and hence need to be supplied in the foods. |
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Classification of Vitamins |
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Fat soluble vitamins
These vitamins are soluble in fats, oils and in fat solvents like alcohol, etc. There are four fat soluble vitamins. They are: Vitamin A, Vitamin D, Vitamin E and Vitamin K. |
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Some Important Vitamins |
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This is a fat soluble vitamin which is present mostly in animals. Its provitamins carotenes are found in plants. Vitamin A is necessary for vision and proper growth. It is necessary for maintenance of proper immune system to fight various infections. Cholesterol synthesis requires vitamin A. The carotenoids act as antioxidants and reduce risk of cancers. |
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Functions of Vitamins in Biosystems |
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Vitamins are the important food factors required in diet. Different vitamins are involved in different biochemical functions. They are required in very low concentration, the daily requirement of any vitamin for any individual is extremely smell. The daily dose of any vitamin is not a fixed quantity but varies according to size, age and rate of metabolism of the individual. Youngsters need higher quantity of vitamins then elders and their requirement increases when a person performs exercise. Growing children and pregnant mothers need more quantity of vitamins in their diet. |
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Summary |
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Biochemistry is the branch of chemistry which deals with the study of chemical composition and structure of living organism and chemical changes take place in them. |
