Biology · Chapter 4
Study notes aligned to the official NEB syllabus.
Biomolecules are the chemical substances that make up living organisms and are essential for life. This chapter covers the inorganic and organic life components, the four major biomolecules (carbohydrates, proteins, lipids and nucleic acids) and enzymes.
Various chemical substances are the basic constituents of living organisms and are essential for growth, development and the maintenance of life. These substances are called life components. They are of two types:
Inorganic life components are simple chemical substances that are also essential for living organisms. They are of two types: water and mineral nutrients.
Water is the most abundant inorganic compound in cells. It makes up 60 to 70% of body weight and 75 to 90% of the protoplasm. It does not yield energy but is vital for the maintenance of life. A water molecule is formed by the combination of two hydrogen atoms and one oxygen atom joined by covalent bonds, and hydrogen bonds form between water molecules. The bond angle between the hydrogen and oxygen atoms is 104.5°.
Biological functions of water:
Mineral nutrients are chemical elements essential for the growth and development of organisms. About 27 chemical elements are necessary for the growth and development of living organisms. They are of two types:
Organic life components are complex organic compounds essential for the growth, development and maintenance of life, such as carbohydrates, proteins, lipids and nucleic acids. Those organic molecules that are essential for life are called biomolecules (molecules of life). Most of them are macromolecules. The important biomolecules are carbohydrates, proteins, lipids and nucleic acids.
Carbohydrates are complex organic compounds made up of carbon, hydrogen and oxygen. Chemically they are hydrates of carbon (carbon combined with water). Structurally they are polyhydroxy aldehydes or polyhydroxy ketones. They are classified according to their complexity into three groups:
Monosaccharides are simple sugars with the general formula Cn(H2O)n, containing 3 to 7 carbon atoms. They cannot be hydrolyzed into smaller carbohydrates. Common examples are glucose, fructose and galactose. Sugars containing a ketone group are called ketoses. According to the number of carbon atoms, they are classified as: