The Structure and Function of Large Biological Molecules

Chapter 5: The Structure and Function of Large Biological Molecules

Molecules of Life

All living things are composed of four major classes of large biological molecules, which are essential for structure and function in cells.

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Macromolecules are large, complex molecules formed by the polymerization of smaller subunits called monomers.

The Synthesis and Breakdown of Polymers

Macromolecules are assembled and disassembled through specific chemical reactions involving water.

• Dehydration Reaction: A chemical reaction in which two monomers are covalently bonded to each other with the removal of a water molecule. This process builds polymers from monomers.

• Hydrolysis: A chemical reaction that breaks bonds between monomers by the addition of water, essentially the reverse of a dehydration reaction. This process disassembles polymers into monomers.

The Synthesis of Polymers

Polymer synthesis involves the repeated addition of monomers via dehydration reactions, catalyzed by enzymes.

• Dehydration Reaction: Each time a monomer is added to a growing polymer chain, a water molecule is released.

• Enzymes: Specialized macromolecules that speed up chemical reactions, including those that build (polymerase) or break down (hydrolase) polymers.

Example: The formation of a polysaccharide from monosaccharide monomers involves multiple dehydration reactions, each forming a glycosidic bond and releasing water.

The Breakdown of Polymers

Polymers are broken down into their monomer subunits through hydrolysis reactions, which require the addition of water and are catalyzed by specific enzymes.

• Hydrolysis: The bond between monomers is broken by the addition of a water molecule, with a hydrogen from the water attaching to one monomer and a hydroxyl group attaching to the other.

• Enzyme Example: Hydrolase enzymes catalyze hydrolysis reactions.

Example: The digestion of starch into glucose monomers in the human body is accomplished by hydrolysis reactions.

Summary Table: Synthesis and Breakdown of Polymers

Process	Description	Enzyme Type	Water Involved?
Dehydration Reaction	Joins monomers by removing water	Polymerase	Water released
Hydrolysis	Breaks polymers into monomers by adding water	Hydrolase	Water consumed

Additional info: These processes are fundamental to the metabolism of all living organisms, enabling the construction and deconstruction of essential macromolecules.