Biomolecules: An Overview

Definition and Importance

Biomolecules are organic molecules essential to living organisms. They play critical roles in structure, function, and regulation of the body's tissues and organs. There are four primary classes of biomolecules:

• Carbohydrates

• Proteins

• Nucleic Acids

• Lipids

Each class has unique structures and functions vital for life.

Monomers and Polymers

Basic Concepts

• Monomers: Single, small molecular units that can be repetitively linked to form polymers.

• Polymers: Long chains of many monomers linked together by covalent bonds.

• Carbohydrates, proteins, and nucleic acids are polymers made from consistent monomers; lipids are not true polymers.

Examples:

• Carbohydrate monomer: Monosaccharide

• Protein monomer: Amino acid

• Nucleic acid monomer: Nucleotide

Polymerization and Depolymerization

• Dehydration Synthesis: Forms covalent bonds between monomers by removing a water molecule, building a polymer.

• Hydrolysis: Breaks covalent bonds in polymers by adding a water molecule, releasing monomers.

Equation for Dehydration Synthesis:

Equation for Hydrolysis:

Carbohydrates

Structure and Classification

Carbohydrates are carbon-based molecules hydrated with many hydroxyl groups (–OH). They are also called saccharides (from the Greek for "sugar"). The general formula for many simple carbohydrates is .

• Monosaccharides: Single sugar units (e.g., glucose, fructose).

• Oligosaccharides: Short chains of 2–20 covalently linked monosaccharides (e.g., maltose, sucrose).

• Polysaccharides: Long chains (polymers) of monosaccharides (e.g., starch, cellulose, glycogen).

Formation and Breakdown of Polysaccharides

• Dehydration Synthesis links monosaccharides to build polysaccharides via glycosidic bonds.

• Hydrolysis breaks down polysaccharides into individual monosaccharides.

Example: Formation of maltose from two glucose molecules by dehydration synthesis.

Functions of Carbohydrates

• Structural Support: Polysaccharides like cellulose (plants) and chitin (insects, fungi) provide rigidity and protection.

• Energy Storage: Starch (plants) and glycogen (animals) store energy for short-term use.

Lipids

Overview

Lipids are a diverse group of hydrophobic molecules that do not form true polymers. They include fats, phospholipids, and steroids. Lipids are important for energy storage, membrane structure, and signaling.

• Fats: Composed of glycerol and fatty acids; function in long-term energy storage and insulation.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Characterized by four fused carbon rings; include cholesterol and hormones.

Additional info: Not all lipids are fats; some function as hormones or structural components.

Proteins

Structure and Function

Proteins are polymers of amino acids linked by peptide bonds. They are essential for structure, function, and regulation of tissues and organs.

• Enzymatic activity: Catalyze biochemical reactions.

• Structural support: Provide support in cells and tissues (e.g., collagen).

• Transport: Move substances across membranes (e.g., hemoglobin).

• Defense: Antibodies protect against disease.

• Signaling: Hormones and receptors transmit signals.

Levels of Protein Structure:

1. Primary: Sequence of amino acids.

2. Secondary: Local folding (α-helix, β-sheet) via hydrogen bonds.

3. Tertiary: 3D shape from R-group interactions.

4. Quaternary: Association of multiple polypeptide chains.

Nucleic Acids

Structure and Function

Nucleic acids store, transmit, and help express hereditary information. The two main types are:

• Deoxyribonucleic acid (DNA): Stores genetic information.

• Ribonucleic acid (RNA): Involved in protein synthesis and gene expression.

Nucleic acids are polymers of nucleotides, each consisting of a nitrogenous base, a pentose sugar, and one or more phosphate groups.

Central Dogma of Molecular Biology:

DNA → RNA → Protein

Summary Table: Classes of Biomolecules