Structure and Function of Biological Macromolecules: Polymers and Monomers

Chapter 5: The Structure and Function of Large Biological Molecules

Learning Objectives

• Explain the processes by which polymers are assembled and disassembled.

• Describe the structures and functions of simple and complex carbohydrates.

• Describe the structures of three kinds of lipids and explain their functions.

• List the main functions of proteins and describe the structures of amino acids and proteins.

• Compare and contrast the structures of DNA and RNA and their component nucleotides, and describe the functions of these polynucleotides.

Overview: Classes of Biological Molecules

Main Classes

Biological molecules are essential for life and are classified into four major groups: carbohydrates, proteins, nucleic acids, and lipids. Three of these classes (carbohydrates, proteins, nucleic acids) are macromolecules that form polymers, while lipids are not true polymers.

• Carbohydrates: Serve as energy sources and structural materials. Example: Glucose (monomer), Starch (polymer).

• Proteins: Perform a wide range of functions including catalysis, structure, transport, and signaling. Example: Amino acid (monomer), Alcohol dehydrogenase (protein).

• Nucleic acids: Store and transmit genetic information. Example: Nucleotide (monomer), DNA (polymer).

• Lipids: Important for energy storage, membrane structure, and signaling. Example: Phospholipid.

Macromolecules: Polymers and Monomers

Definition of Macromolecules

Three of the four classes of macromolecules—carbohydrates, proteins, and nucleic acids—form chain-like molecules called polymers.

• Polymer: A long molecule made up of many similar or identical building blocks (monomers) connected by covalent bonds.

• Monomer: The repeated units in a polymer; small molecules that serve as the building blocks of polymers.

Synthesis and Breakdown of Polymers

Role of Enzymes

Enzymes are specialized macromolecules that speed up chemical reactions in cells, including the assembly and disassembly of polymers.

Synthesis: Dehydration Reaction

Polymers are formed by joining monomers through dehydration reactions, which involve the loss of a water molecule.

• Monomers are connected by covalent bonds.

• One monomer provides a hydroxyl group (–OH), the other provides a hydrogen atom (–H).

• Together, they form H2O (water), which is removed during the reaction.

• Energy is required for the reaction.

Equation:

$\text{Monomer}_1{-OH} + \text{Monomer}_2{-H} \xrightarrow{\text{Enzyme}} \text{Polymer} + H_2O$

Breakdown: Hydrolysis Reaction

Polymers are broken down into monomers by hydrolysis, which is the reverse of dehydration.

• Water is added to break the bonds between monomers.

• A hydrogen atom (–H) attaches to one monomer.

• A hydroxyl group (–OH) attaches to the adjacent monomer.

• Energy is released during the reaction.

• Example: Digestion of food polymers into monomers.

Equation:

$\text{Polymer} + H_2O \xrightarrow{\text{Enzyme}} \text{Monomer}_1{-OH} + \text{Monomer}_2{-H}$

Visual Summary: Dehydration and Hydrolysis

• Dehydration: Short polymer + unlinked monomer → longer polymer + water removed.

• Hydrolysis: Polymer + water added → shorter polymer + monomer released.

Exam Practice Questions

• Polymers are made of monomer subunits that are joined by what type of bonds? Answer: Covalent bonds

• Monomers are joined together to form polymers by: Answer: Dehydration reaction

• Polymers are broken down to form monomers by: Answer: Hydrolysis reaction

• Energy is required in: Answer: Dehydration reaction

• Energy is released in: Answer: Hydrolysis reaction

Summary Table: Polymer Formation and Breakdown

Process	Reaction Type	Water Involved	Energy	Bond Formed/Broken
Polymer Synthesis	Dehydration	Water removed	Required	Covalent bond formed
Polymer Breakdown	Hydrolysis	Water added	Released	Covalent bond broken

Key Terms

• Macromolecule: Large molecule composed of thousands of atoms.

• Polymer: Chain-like molecule made of repeating monomer units.

• Monomer: Small molecule that serves as a building block for polymers.

• Dehydration reaction: Chemical reaction that joins monomers by removing water.

• Hydrolysis: Chemical reaction that breaks polymers into monomers by adding water.

• Enzyme: Biological catalyst that speeds up chemical reactions.

Additional info: Later sections of the chapter (not shown in these slides) would cover the detailed structures and functions of carbohydrates, proteins, nucleic acids, and lipids, including examples and biological roles.