Large Biological Molecules: Structure, Function, and Synthesis

Large Biological Molecules

Introduction to Macromolecules

All living organisms are composed of four major classes of large biological molecules, also known as macromolecules. These molecules are essential for life and include carbohydrates, lipids, proteins, and nucleic acids. Most macromolecules are polymers, which are long chains of repeating subunits.

• Carbohydrates: Serve as energy sources and structural materials.

• Lipids: Include fats, oils, and phospholipids; important for energy storage and membrane structure.

• Proteins: Perform a wide variety of functions including catalysis, transport, and structural support.

• Nucleic Acids: Store and transmit genetic information.

Example: Nutrition labels list macromolecules such as carbohydrates, proteins, and fats, reflecting their dietary importance.

Macromolecules as Polymers

Polymers and Monomers

Most biological macromolecules are polymers, which are molecules made up of many similar or identical building blocks called monomers linked by covalent bonds.

• Polymer: A long molecule consisting of many monomers.

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

Synthesis & Breakdown of Polymers

Dehydration Reaction

Polymers are synthesized by dehydration reactions, in which two monomers become covalently bonded to each other with the removal of a water molecule.

• Dehydration Reaction: Joins monomers to form polymers by releasing water.

Hydrolysis

Polymers are broken down into monomers by hydrolysis, a process that adds a water molecule to break the covalent bond between monomers.

• Hydrolysis: Breaks polymers into monomers by adding water.

Equation:

• Dehydration: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis: $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Example: The synthesis of a protein from amino acids involves repeated dehydration reactions forming peptide bonds.

Enzymes in Polymer Synthesis and Breakdown

Role of Enzymes

Enzymes are biological catalysts that speed up chemical reactions, including dehydration and hydrolysis, without being consumed in the process.

• Enzyme: A protein molecule that increases the rate of a reaction.

• Enzymes are required for both the formation and breakdown of polymers.

Example: Digestive enzymes hydrolyze food polymers into monomers for absorption.

Formation of Specific Bonds in Macromolecules

Peptide Bonds in Proteins

Proteins are formed by linking amino acids through peptide bonds, which are covalent bonds formed by dehydration synthesis between the amino group of one amino acid and the carboxyl group of another.

• Peptide Bond: $\text{Amino Acid}_1 + \text{Amino Acid}_2 \rightarrow \text{Dipeptide} + H_2O$

Phosphodiester Bonds in Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides linked by phosphodiester bonds, formed by dehydration reactions between the phosphate group of one nucleotide and the sugar of another.

• Phosphodiester Bond: $\text{Nucleotide}_1 + \text{Nucleotide}_2 \rightarrow \text{Dinucleotide} + H_2O$

Example: The backbone of DNA consists of alternating sugar and phosphate groups connected by phosphodiester bonds.

Summary Table: Macromolecules and Their Bonds

Macromolecule	Monomer	Bond Type	Example
Carbohydrate	Monosaccharide	Glycosidic bond	Starch, cellulose
Protein	Amino acid	Peptide bond	Hemoglobin, enzymesa
Nucleic Acid	Nucleotide	Phosphodiester bond	DNA, RNA
Lipid	Fatty acid & glycerol	Ester bond	Triglyceride, phospholipid

Learning Objectives

• Describe how macromolecules are made and broken down.

• Identify and describe the macromolecules: carbohydrates, lipids, proteins, nucleic acids.

• Explain the relevance of genomic sequencing in biology.

Additional info: These notes are based on introductory slides for a General Biology course, focusing on the chemistry and biology of macromolecules. The content is suitable for college-level biology students preparing for exams or seeking a concise overview of Chapter 5: Large Biological Molecules.