Macromolecules I: Structure, Function, and Synthesis in Biology

Macromolecules: Overview

Definition and Biological Importance

Macromolecules are large, complex molecules essential for life, composed of smaller subunits called monomers. They play critical roles in structure, function, and energy storage within living organisms.

• Key Classes of Macromolecules: Carbohydrates, Lipids, Proteins, Nucleic Acids

• All macromolecules contain carbon, hydrogen, and oxygen; some also contain nitrogen, phosphorus, or sulfur.

• Foods such as bread, grains, fruits, and cheese are rich sources of macromolecules.

Monomers vs Polymers

Structural Organization

Macromolecules are built from individual subunits (monomers) that are covalently bonded to form polymers.

• Monomers: Small, repeating units (e.g., glucose, amino acids, nucleotides).

• Polymers: Long chains of monomers linked by covalent bonds (e.g., starch, proteins, DNA).

• Polymerization is the process of joining monomers to form polymers.

Synthesis vs Hydrolysis Reactions

Formation and Breakdown of Polymers

Biological macromolecules are assembled and disassembled through two key types of chemical reactions: dehydration synthesis and hydrolysis.

• Dehydration Synthesis (Condensation Reaction): Two monomers are joined by removing a water molecule, forming a covalent bond.

• Example: Two glucose molecules combine to form maltose (a disaccharide) and water.

• $\text{Glucose} + \text{Glucose} \xrightarrow{\text{Dehydration}} \text{Maltose} + \text{H}_2\text{O}$

• Hydrolysis Reaction: Polymers are broken down into monomers by adding water; one monomer receives a hydrogen ion (H+), the other a hydroxyl group (OH-).

• Example: Maltose is split into two glucose molecules by hydrolysis.

• $\text{Maltose} + \text{H}_2\text{O} \xrightarrow{\text{Hydrolysis}} \text{Glucose} + \text{Glucose}$

Enzymes and Catalysis

Role of Biological Catalysts

Reactions involving macromolecules are catalyzed by enzymes, which are biological molecules that accelerate chemical reactions.

• Enzymes: Specialized proteins that speed up hydrolysis and dehydration reactions.

• Dehydration reactions: Form new bonds and require energy.

• Hydrolysis reactions: Break bonds and release energy.

• Each class of macromolecule has specific enzymes for its breakdown:

  • Carbohydrates: Broken down by amylase, sucrase, lactase

  • Lipids: Broken down by lipases

  • Proteins: Broken down by pepsin and peptidase

Carbohydrates

Structure, Types, and Functions

Carbohydrates are organic molecules that provide energy and structural support. They are found in grains, fruits, and vegetables.

• Function: Main source of energy for the body, typically in the form of glucose.

• General Formula: $\text{(CH}_2\text{O)}_n$

• Elemental Ratio: Carbon:Hydrogen:Oxygen is typically 1:2:1.

• Types of Carbohydrates:

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

  • Disaccharides: Two monosaccharides joined together (e.g., sucrose, maltose, lactose)

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

• Examples: Bananas, potatoes, bread, and beans are rich in carbohydrates.

Additional info:

• Macromolecules are fundamental to cell structure and function, and their synthesis and breakdown are tightly regulated by enzymes.

• Understanding the chemistry of macromolecules is essential for studying metabolism, genetics, and cell biology.