Molecules of Life: Structure and Function of Biological Macromolecules

Molecules of Life

Introduction to Biological Macromolecules

All living organisms are composed of four major classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids. These molecules are essential for structure, function, and regulation of the body's tissues and organs.

• Macromolecules are large molecules, often polymers, made up of repeating subunits called monomers.

• Of the four classes, carbohydrates, proteins, and nucleic acids are true polymers.

• Lipids are not polymers but are considered macromolecules due to their large size and complex structure.

Polymers and Monomers

Polymers are long molecules consisting of many similar or identical building blocks linked by covalent bonds. The repeating units are called monomers.

• Dehydration reaction: A chemical reaction in which two monomers are covalently bonded to each other with the removal of a water molecule, forming a longer polymer.

• Hydrolysis: The process of breaking down polymers into monomers by adding a water molecule, which breaks the covalent bond.

Example: The synthesis of a protein from amino acids involves repeated dehydration reactions, while digestion of starch into glucose involves hydrolysis.

Carbohydrates

Functions and Types

Carbohydrates serve as fuel and building material in living organisms. They are classified based on the number of sugar units:

• Monosaccharides: Single sugar molecules (e.g., glucose).

• Disaccharides: Two monosaccharides joined by a glycosidic bond.

• Polysaccharides: Polymers composed of many monosaccharide units.

Monosaccharides

Monosaccharides are the simplest carbohydrates and are classified by:

• The location of the carbonyl group (as an aldose [aldehyde sugar] or ketose [ketone sugar]).

• The number of carbons in the carbon skeleton (trioses, pentoses, hexoses, etc.).

Example: Glucose (C6H12O6) is the most common monosaccharide.

Classification Table: Monosaccharides

	Aldose (Aldehyde Sugar)	Ketose (Ketone Sugar)
Trioses (3C)	Glyceraldehyde	Dihydroxyacetone
Pentoses (5C)	Ribose	Ribulose
Hexoses (6C)	Glucose, Galactose	Fructose

Linear and Ring Forms

Although monosaccharides are often drawn as linear skeletons, in aqueous solutions many sugars form rings. This ring structure is more stable and is the predominant form in biological systems.

• Ring formation occurs when the carbonyl group reacts with a hydroxyl group on the same molecule.

Disaccharides

A disaccharide is formed when a dehydration reaction joins two monosaccharides. The covalent bond formed is called a glycosidic bond.

• Example: Sucrose (table sugar) is a disaccharide formed from glucose and fructose.

*Additional info: The notes and images provided are consistent with introductory college-level General Biology content, specifically focusing on the chemistry of life and the structure and function of carbohydrates as biological macromolecules.*