The Structure and Function of Large Biological Molecules

Large Biological Molecules

Introduction to Macromolecules

Large biological molecules, also known as macromolecules, are essential to the structure and function of living organisms. Most macromolecules are polymers, which are long chains composed of repeating subunits called monomers. The four major classes of biological macromolecules are carbohydrates, proteins, nucleic acids, and lipids (though lipids are not true polymers).

• Polymer: A long molecule consisting of many similar or identical building blocks linked by covalent bonds.

• Monomer: The repeating unit that serves as the building block of a polymer.

• Macromolecule: A very large molecule, such as a protein, nucleic acid, or polysaccharide, with a molecular weight in the thousands or millions.

Carbohydrates, proteins, and nucleic acids are polymers, while lipids are large molecules that do not form true polymers.

Synthesis and Breakdown of Polymers

Dehydration and Hydrolysis Reactions

The formation and breakdown of polymers involve two key types of chemical reactions: dehydration reactions and hydrolysis.

• Dehydration Reaction: Occurs when two monomers bond together through the loss of a water molecule. This reaction synthesizes polymers from monomers.

• Hydrolysis: Polymers are disassembled to monomers by hydrolysis, a reaction that adds a water molecule, breaking a bond. Hydrolysis is essentially the reverse of the dehydration reaction.

Enzymes are specialized macromolecules (usually proteins) that speed up chemical reactions, including those that make or break down polymers.

Dehydration Reaction Example

• When a short polymer and an unlinked monomer join, a water molecule is released, forming a longer polymer.

• General equation: $\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Dehydration}} \text{Polymer} + H_2O$

Hydrolysis Reaction Example

• When a polymer is broken down, a water molecule is added, breaking the bond between monomers.

• General equation: $\text{Polymer} + H_2O \xrightarrow{\text{Hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Classes of Biological Macromolecules

Overview of the Four Major Classes

Each class of biological macromolecule has a unique structure and function in living organisms.

Class	Monomer (if applicable)	Polymer (if applicable)	Example	Main Function
Carbohydrates	Monosaccharide	Polysaccharide	Starch, Glucose	Energy storage, structural support
Proteins	Amino acid	Polypeptide	Enzymes, Hemoglobin	Catalysis, transport, structure, signaling
Nucleic Acids	Nucleotide	Polynucleotide	DNA, RNA	Genetic information storage and transfer
Lipids	Fatty acids, glycerol (not true monomers)	Not true polymers	Phospholipids, Fats	Membrane structure, energy storage

Key Points

• Carbohydrates: Serve as fuel and building material. Monosaccharides (simple sugars) are the monomers; polysaccharides (e.g., starch, cellulose) are the polymers.

• Proteins: Perform a vast array of functions, including catalysis (enzymes), transport, and structural roles. Built from amino acid monomers.

• Nucleic Acids: Store and transmit hereditary information. DNA and RNA are polymers of nucleotide monomers.

• Lipids: Diverse group including fats, phospholipids, and steroids. Not true polymers, but essential for energy storage and membrane structure.

Examples and Applications

• Starch (a carbohydrate) is a storage polysaccharide in plants.

• Hemoglobin (a protein) transports oxygen in the blood.

• DNA (a nucleic acid) encodes genetic instructions for the development and functioning of living things.

• Phospholipids (a lipid) form the fundamental structure of cell membranes.

Additional info: The provided slides and notes are foundational for understanding the chemical basis of life, a core topic in General Biology. The content covers the essential macromolecules, their structure, synthesis, and function, which are critical for further study in cell biology, genetics, and physiology.