Chapter 5: The Structure and Function of Large Biological Molecules

Chapter 5: The Structure and Function of Large Biological Molecules

Overview of Biological Macromolecules

Large biological molecules are essential for life and include carbohydrates, proteins, nucleic acids, and lipids. These molecules have distinct structures and functions, and most are polymers built from smaller units called monomers.

• Carbohydrates: Serve as fuel and building material; monomer is glucose.

• Proteins: Perform a wide range of functions including catalysis, defense, and transport; monomer is amino acid.

• Nucleic Acids: Store and transmit genetic information; monomer is nucleotide.

• Lipids: Diverse group, not true polymers; include fats, phospholipids, and steroids.

Macromolecules as Polymers (Concept 5.1)

Most large biological molecules are polymers, which are long chains of repeating units called monomers. The diversity of macromolecules arises from the arrangement and type of monomers.

• Macromolecule: A large molecule formed by polymerization of smaller subunits.

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

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

• Examples: Carbohydrates, proteins, and nucleic acids are polymers; lipids are not true polymers.

Synthesis and Breakdown of Polymers

Polymers are assembled and disassembled by specific chemical reactions, often catalyzed by enzymes.

• Enzymes: Specialized macromolecules that speed up chemical reactions.

• Dehydration Reaction: Two monomers are covalently bonded through the loss of a water molecule, forming a polymer.

• Hydrolysis: Polymers are broken down into monomers by the addition of a water molecule, reversing the dehydration reaction.

Equations:

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

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

Diversity of Polymers

Cells contain thousands of different macromolecules, which vary among cells, species, and even more between species. The vast diversity of polymers is possible because a small set of monomers can be arranged in many different ways.

• Key Point: The arrangement and sequence of monomers in polymers lead to molecular diversity and biological specificity.

• Example: Proteins are made from 20 different amino acids, allowing for immense structural and functional variety.

Table: Comparison of Biological Macromolecules

Class	Monomer	Polymer	Main Function
Carbohydrates	Monosaccharide (e.g., glucose)	Polysaccharide (e.g., starch)	Energy storage, structural support
Proteins	Amino acid	Polypeptide/protein	Catalysis, transport, defense, structure
Nucleic Acids	Nucleotide	Polynucleotide (DNA, RNA)	Genetic information storage and transmission
Lipids	Fatty acid, glycerol	Not true polymers	Energy storage, membrane structure, signaling

Illustrative Example: Polymerization and Hydrolysis

• Polymerization: Formation of starch from glucose monomers via dehydration reactions.

• Hydrolysis: Digestion of proteins into amino acids in the stomach.

Additional info: These notes summarize the introductory concepts of macromolecules, their polymeric nature, and the chemical reactions involved in their synthesis and breakdown, as presented in the Campbell Biology textbook and lecture slides.