Chapter 2: Chemical Composition of the Body – Biomolecules

Introduction to Biomolecules

Biomolecules are organic molecules essential for life, forming the chemical foundation of all living organisms. They are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. The four major classes of biomolecules are carbohydrates, lipids, proteins, and nucleic acids. Each class has unique structures and functions vital to cellular processes and the physiology of the human body.

Common Functional Groups Found in Biomolecules

Functional groups are specific groups of atoms within molecules that determine the characteristic chemical reactions of those molecules. The presence and arrangement of these groups influence the properties and reactivity of biomolecules.

Example: The carboxyl group (-COOH) is found in amino acids and gives them acidic properties, while the amino group (-NH2) acts as a base.

Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically with the general formula or . They serve as a major source of energy and are also important for structural purposes in cells.

• Function: Major source of energy (especially hexoses like glucose).

• Structure: Ribose and deoxyribose (pentoses) are found in nucleic acids.

• Types:

  • Monosaccharides

  • Disaccharides

  • Polysaccharides

Example: Glucose is a primary energy source for most cells.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates, often referred to as simple sugars. They are the building blocks for more complex carbohydrates.

• Hexoses: Six-carbon sugars (e.g., glucose, fructose, galactose) with the formula .

• Pentoses: Five-carbon sugars (e.g., ribose, deoxyribose) important in nucleic acids.

• Monosaccharides are typically ring-shaped in aqueous solutions and are polar due to multiple hydroxyl (-OH) groups.

Example: Glucose, fructose, and galactose are all hexose sugars but differ in the arrangement of atoms, leading to different properties and functions.

Structure of Monosaccharides

The structure of monosaccharides can be represented as either straight chains or rings. In biological systems, the ring form is most common. The position of the carbonyl group (C=O) determines whether the sugar is an aldose (aldehyde group) or a ketose (ketone group).

Example: The difference between glucose and galactose is the orientation of the hydroxyl group on carbon 4.

Additional info: Monosaccharides are classified based on the number of carbon atoms (triose, pentose, hexose) and the type of carbonyl group (aldose or ketose). Their polarity allows them to dissolve easily in water, making them readily available for cellular metabolism.