Biomolecules: An Overview

Main Classes of Biomolecules

Biomolecules are essential organic compounds that form the basis of life. The four major classes of biomolecules found in living organisms are:

• Carbohydrates

• Proteins

• Lipids (fats)

• Nucleic acids

Each class has unique monomer subunits and plays distinct biological roles in structure, and information storage.

Monomers and Polymers

Monomer Subunits and Polymerization

Biomolecules are often polymers, meaning they are composed of repeating subunits called monomers. The process of linking monomers to form polymers is called polymerization.

• Proteins: Monomers are amino acids, linked by peptide bonds.

• Carbohydrates: Monomers are monosaccharides (simple sugars), linked by glycosidic bonds.

• Lipids: Not true polymers but often formed from fatty acids and glycerol via ester bonds.

• Nucleic acids: Monomers are nucleotides, linked by phosphodiester bonds.

Polymerization typically occurs via dehydration reactions, while breakdown occurs via hydrolysis.

Polymerization Reactions

Dehydration and Hydrolysis

Polymer formation and breakdown are governed by two key chemical reactions:

• Dehydration Reaction (Condensation): Joins two monomers by removing a water molecule, forming a new covalent bond.

• Hydrolysis: Breaks a covalent bond in a polymer by adding a water molecule, resulting in smaller subunits.

These reactions are catalyzed by specialized enzymes.

Carbohydrates

Structure and Function

Carbohydrates are composed of monosaccharide monomers such as glucose and fructose. They serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose = glucose + fructose).

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

Carbohydrates are linked by glycosidic bonds formed via dehydration reactions.

Proteins

Structure and Levels of Organization

Proteins are polymers of amino acids, joined by peptide bonds. They perform a wide range of functions including catalysis, structural support, transport, and signaling.

• Primary structure: Sequence of amino acids in a polypeptide chain.

• Secondary structure: Local folding patterns (e.g., alpha helix, beta sheet) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape of a single polypeptide, determined by interactions among R groups.

• Quaternary structure: Association of multiple polypeptide chains (e.g., hemoglobin).

Protein structure is sensitive to environmental factors such as pH and temperature. Loss of structure is called denaturation.

Lipids

Structure and Function

Lipids are hydrophobic molecules, primarily composed of fatty acids and glycerol. They are important for energy storage, membrane structure, and signaling.

• Fatty acids: Long hydrocarbon chains with a carboxyl group.

• Triglycerides: Three fatty acids linked to glycerol via ester bonds.

• Phospholipids: Major component of cell membranes.

Lipids are not true polymers but are assembled from smaller components.

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) are polymers of nucleotides, which consist of a nitrogenous base, a pentose sugar, and a phosphate group. They store and transmit genetic information.

• DNA: Deoxyribonucleic acid; double-stranded helix; stores genetic information.

• RNA: Ribonucleic acid; single-stranded; involved in protein synthesis and gene regulation.

Nucleotides are joined by phosphodiester bonds between the phosphate group and the sugar.

Base Pairing and Antiparallel Strands

DNA strands are antiparallel and held together by complementary base pairing:

• Adenine (A) pairs with Thymine (T)

• Guanine (G) pairs with Cytosine (C)

This ensures accurate replication and transmission of genetic information.

Summary Table: Biomolecule Classes

Key Equations

• Dehydration Reaction:

• Hydrolysis Reaction:

Additional info:

• Enzymes are biological catalysts that facilitate both dehydration and hydrolysis reactions.

• Protein folding is assisted by molecular chaperones, which help achieve proper tertiary and quaternary structures.

• Denaturation is often irreversible and can result from extreme pH or temperature changes.