BackChapter 5 Part A: Structure and Function of Large Biological Molecules
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Chapter 5: Structure and Function of Large Biological Molecules
Overview: The Molecules of Life
All living organisms are composed of four major classes of large biological molecules. These molecules are essential for structure, function, and regulation of the body's tissues and organs.
Polysaccharides (often grouped as carbohydrates, which also includes sugars)
Proteins
Nucleic acids
Lipids
Within cells, small organic molecules such as sugars and amino acids are joined together to form larger molecules. Macromolecules are large molecules composed of thousands of covalently connected atoms. Polysaccharides, proteins, and nucleic acids are typically much larger than lipids. Understanding the molecular structure of these molecules is critical because structure and function are inseparable in biology.
Macromolecules and Polymers
Most biological macromolecules (except lipids) are polymers, which are long molecules consisting of many similar or identical building blocks called monomers. These monomers are often linked by covalent bonds.
Polymer: A long molecule made up of repeating subunits (monomers).
Monomer: The repeating unit or building block of a polymer.
Three of the four classes of life's organic molecules are polymers:
Polysaccharides
Proteins
Nucleic acids
Lipids are macromolecules but are not polymers.
Biological polymers are made and broken down by similar chemical mechanisms, often facilitated by enzymes—macromolecules that speed up (catalyze) chemical reactions.
The Synthesis and Breakdown of Polymers
Polymers are assembled and disassembled by two main types of reactions:
Dehydration (Synthesis) Reaction: A reaction in which two monomers are covalently bonded to each other with the loss of a water molecule. This process is also called a condensation reaction.
Hydrolysis: The reverse of dehydration synthesis. In hydrolysis, a water molecule is added, breaking the bond between monomers.
Example: Formation of a longer polymer from a short polymer and an unlinked monomer by removing a water molecule.
Equation for Dehydration Synthesis:
Equation for Hydrolysis:
The Diversity of Polymers
Each cell contains thousands of different kinds of macromolecules. The immense variety of polymers can be built from a small set of monomers, similar to how many words can be formed from a limited alphabet. Despite this diversity, molecular structure and function can be grouped into the four main classes discussed above.
Summary Table: Classes of Large Biological Molecules
Class | Monomer (Subunit) | Polymer | Main Functions |
|---|---|---|---|
Carbohydrates (Polysaccharides) | Monosaccharides | Polysaccharides | Energy storage, structural support |
Proteins | Amino acids | Polypeptides (proteins) | Catalysis, structure, transport, signaling |
Nucleic acids | Nucleotides | DNA, RNA | Information storage and transfer |
Lipids | Fatty acids, glycerol (not true polymers) | Fats, phospholipids, steroids | Energy storage, membrane structure, signaling |
Additional info: Later sections of the chapter (not shown in these slides) would cover the detailed structure and function of each class, including examples such as starch, cellulose, glycogen (carbohydrates), triglycerides, phospholipids, steroids (lipids), and the structure of proteins and nucleic acids.
