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Introduction |
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The living cells contain specific macromolecules with a high molecular weight and a poor solubility. Generally in a cell, macromolecules are represented by polysaccharides, proteins, nucleic acids and enzymes. These compounds are formed by polymerisation of micromolecules such as sugars, amino acids and nucleotides. |
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Polysaccharides |
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Polysaccharides are complex carbohydrates formed from monosaccharides. A number of monosaccharide molecules such as those of glucose, become linked by glycosidic bonds with the elimination of a molecule of water for each monosaccharide added. When a polysaccharide has multiple molecules of the same type, it is described as homopolysaccharide. For example, starch and glycogen are composed of only glucose. When a polysaccharide molecule is formed by more than one type of monosaccharide molecules, it is described as a heteropolysaccharide. For example, chitin and agar. |
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Proteins |
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Proteins are polymers of amino acids. Each protein is a linear, unbranched, polypeptide molecule. The order in which amino acids occur is specific for each polypeptide. The protein molecules are very large and highly complex macromolecules. Insulin (human) has 53 amino acids arranged in two polypeptide chains of 22 and 31 amino acids. Human serum albumin has 582 amino acids in its polypeptide chain. |
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Nucleic Acids |
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Nucleic acids are giant macromolecules having a complex structure and very high molecular weight. They are polymers of nucleotides and hence, described as polynucleotides. |
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Deoxyribose Nucleic Acid (DNA) |
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With the exception of a few viruses, DNA forms the genetic material in all living organisms. In the prokaryotic cells DNA occurs in the cytoplasm. In the eukaryotic cells it is confined largely to the nucleus and forms the main component of chromosomes. A small amount of DNA is found in the cytoplasm in the organelles like mitochondria and plastids. It is called extra- nuclear DNA. |
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Ribose Nucleic Acid (RNA) |
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RNA occurs mostly in the cytoplasm in the eukaryotic cells. A small amount occurs in the nucleus of the cell, as a constituent of nucleolus. RNA is a single polynucleotide chain composed of nucleotides of adenine, guanine, cytosine and uracil. Thymine nucleotides are absent. |
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Enzymes and Inorganic Catalysts |
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Enzymes resemble inorganic catalysts in several aspects and differ from them in many other features. There are two different views to explain the mode of enzyme action the lock and key hypothesis and the induced-fit hypothesis. |
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Classification of Enzymes |
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Enzymes are generally classified on the basis of the type of reactions that they catalyse. 6 groups of enzymes can be recognised on this basis. The following table lists the 6 groups of enzymes along with example. |
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Summary |
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The macromolecules found in a cell are large molecules with a complex structure and very high molecular weight. They are represented by polysaccharides, proteins and nucleic acids. |
