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The sweetest substance is not a sugar The sweetest substance is not a sugar Among the five basic tastes, sweetness is regarded as a pleasurable experience. Sugars are carbohydrates, the biological macromolecules which are most commonly associated with sweetness. Fructose is the sweetest of all the sugars, but the incredible thing to know is that‐ the sweetest substance known to man is not a carbohydrate, it is a protein called Thaumatin which is 2000 ‐ 2500 times sweeter than the table sugar, sucrose. Thaumatococcus is a monotypic genus of tropical flowering plant, containing the single species Thaumatococcus danielli( katemfe fruit), known for being the natural source of Thaumatin. In this chapter you will know about the significance of macromolecules such as carbohydrates, proteins, enzymes, lipids and nucleic acids.

Learning Objectives

After completing the topic, the student will be able to:

  • List the four main classes of large biological molecules as carbohydrates, lipids, proteins and nucleic acids.
  • Classify the carbohydrates based on number of carbons, number of monomers, functional groups, biological function and reducing behavior.
  • Describe the structure and characteristics of monosaccharides, glucose and fructose, disaccharaides sucrose, maltose and lactose, polysaccharides starch and cellulose.
  • Classify the proteins based on their metabolic function and examine the structure of proteins.
  • Discuss in detail about various types of lipids, fats, oil, phospholipids and steroids.
  • Compare the structural features and functions of DNA and RNA.
Molecules of life Molecules of life The larger biological molecules are called “macromolecules”. Macromolecules are in four main classes: carbohydrates, lipids, proteins and nucleic acids. 20 to 25 percent of living matter consists of macromolecules.

Molecules of life
Water, inorganic ions and a large array of relatively small organic molecules (e.g. sugars, vitamins, fatty acids) account for 75 ‐ 80 percent of living matter by weight. Of these small molecules, water is by far the most abundant. Each type of small molecule has unique properties arising from the orderly arrangement of its atoms. Small organic molecules are joined inside cells, forming larger molecules called macro molecules.

The four main classes of large biological molecules are carbohydrates, lipids, proteins and nucleic acids. 25‐20 percent of living matter consists of macromolecules, including proteins, polysaccharides and DNA. Though all of these groups are organized around carbon, each group has its own special structure and function. Cells acquire and use these two size classes of molecules in fundamentally different ways. Ions, water and many small organic molecules are imported into the cell.

Major constituents of food Major constituents of food Carbohydrates are the chief energy source in our diet. Proteins are important in growth, and repair of body tissues.

Living beings are like factories, which need easily available raw materials. Just as factories need machines, the machines of living organisms are specific protein molecules called enzymes. Enzymes cause chemical changes to convert food into body parts such as tissues, the muscle etc., All this doesn't happen in a single step, but along an assembly line called “metabolic pathway”. Our energy is obtained by burning fuel.

The three major constituents of our food namely carbohydrates, fats and proteins function as fuels, as well as provide raw materials for building our tissues. To understand life, we need to know about the chemical properties and reactions of the organic compounds that make us. DNA provided the molecular basis of the template needed for genetic replications. With this discovery, the field of molecular biology was born ‐ the field essentially owes its origin to chemical basis of life.

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