BIOLOGY BIOMOLECULES

Polysaccharides and Nucleic Acids

Contents ...... 3 Nucleic Acids ...... 6

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Polysaccharides

 Polysaccharides (carbohydrates) are one of the macromolecules present in an acid-insoluble pool.  They are mainly compounds of carbon, hydrogen and oxygen.  Polysaccharides are polymers of monosaccharides (sugars).  The number of monosaccharides in a molecule may range from 10 to several thousands, and hence, they have a high molecular weight.  They can be linear or branched.  Polysaccharides are tasteless and colourless substances.  They are sparingly soluble in water.  Polysaccharides cannot diffuse through the cell membrane.  Polysaccharides, on hydrolysis, form monosaccharide units.

 Polysaccharides are represented by the general formula (C6H10O5)n.  In polysaccharides, monomers are joined by glycosidic linkages.

Diagrammatic Representation of a Part of

 Polysaccharides are of two types:

•They are made of only one type of monosaccharide monomer. Homopolysaccharides •Examples: is made of repeated monomers of ; inulin is made of monomers. •Other examples are glycogen and starch.

•They consist of more than one type of monosccharide Heteropolysaccharides monomer. •Examples: Chitin, mucopolysaccharides

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Classification of Polysaccharides

 On the basis of function, polysaccharides are classified as

Storage Structural Mucopolysaccharides Lignin Polysaccharides Polysaccharides  Reserve food; when  Responsible for the  They are  It is present in needed, they are formation of the heteropolymers the plant cell hydrolysed for the structural framework which have wall and production of energy. of cells. adhesive properties provides and are capable of rigidity to the forming gels. cell wall.  Examples: Starch in  Examples: Cellulose  Examples: - plants, glycogen in in plants, chitin in Mucilages such as animals arthropods and some agar and alginic acid fungi (They are found in plants, bacterial cell walls and body fluids of animals.)

In a polysaccharide chain, the right end is called the reducing end and the left end is called the non-reducing end.

Extra Punch!

 List of some polysaccharides, their types and compositions:

Polysaccharides Type Composition Starch Homopolysaccharide Glucose Cellulose Homopolysaccharide Glucose Glycogen Homopolysaccharide Glucose Chitin Homopolysaccharide N-acetyl glucosamine Inulin Homopolysaccharide Fructose Glycoprotein Heteropolysaccharide Polysaccharide and protein Agar-agar Heteropolysaccharide and sulphuric acid

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 Starch can hold iodine molecules in the helical portion of its structure.

 It imparts blue colour to the starch because the starch–I2 complex is blue in colour.

Functions of Polysaccharides

Storage Food

•Polysaccharides such as starch and glycogen are the storage food in plants and animals, respectively.

Structural Components

•Cellulose and chitin are the structural compounds which provide a framework to cells.

Anticoagulant

•Heparin is a polysaccharide which acts as an anticoagulant and prevents blood clotting.

Energy Source

•Polysaccharides such as starch and glycogen are hydrolysed to produce energy within the body of organisms.

Commercial Substances

•Paper pulp, jute and cotton fibre are cellulosic. •Agar-agar is used as a culture medium. •Pectin is used as jelly.

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Nucleic Acids

 Nucleic acid was discovered by Friedrich Miescher. He isolated it from the nuclei of pus cells.  Miescher also named it nuclein.

Friedrich Miescher

 It was renamed nucleic acid by Richard Altmann. He also discovered the two types of nucleic acids.  Nucleic acids are found in the nucleus, cytoplasm, mitochondria and plastids.  They exhibit complex structures and have a high molecular weight.  They are composed of polynucleotide chains.  Each polynucleotide chain is composed of nucleotides.  Each nucleotide is formed of o Pentose sugar (ribose or deoxyribose) o Nitrogenous base (purine or pyrimidine) o A molecule of phosphoric acid

 The phosphate group of one nucleotide at the 5′-carbon of the sugar is linked to the 3′-carbon of the pentose sugar of the adjacent nucleotide by a phosphodiester bond.  The 3′-5′ phosphodiester bonds provide considerable stability to the polynucleotide chain.

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Types of Nucleic Acids

•Deoxyribose nucleic acid •Nucleotides contain deoxyribose pentose sugar DNA •Present in the nucleus, mitochondria and chloroplasts of eukaryotic cells •Forms a single chromosome in prokaryotic cells

•Ribonucleic acid •Nucleotides contain ribose pentose sugar RNA •Found in the nucleus, nucleolus and cytoplasm •There are three types of RNA - mRNA, tRNA and rRNA

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Functions of Nucleic Acids

DNA

•Acts as the genetic material and carries hereditary information from the parents to the offspring. •Controls the metabolic activity of the cell because it is responsible for the formation of certain necessary enzymatic proteins. •Enables the cell to grow and divide because of protein synthesis. •Is responsible for variation and evolution.

RNA

•All three types of RNA are involved in protein synthesis. •Some RNAs also show enzymatic activities. Examples: Ribozyme, ribonuclease •In certain viruses such as TMV, HIV and influenza virus, RNA is the genetic material.

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