Macromolecules

Macromolecules are large, complex molecules that are fundamental to the structure and function of living organisms. The four major classes of biological macromolecules are carbohydrates, proteins, lipids, and nucleic acids. Each class has unique structures and functions essential for life.

Overview of Macromolecules

• Carbohydrates: Serve as energy sources and provide structural support.

• Proteins: Perform a wide variety of functions, including catalyzing biochemical reactions, structural support, transport, and signaling.

• Lipids: Diverse group of hydrophobic molecules involved in energy storage, membrane structure, and signaling.

• Nucleic Acids: Store and transmit genetic information.

Polymers and Monomers

Most macromolecules (except lipids) are polymers, which are long chains made up of repeating subunits called monomers. These monomers are linked by covalent bonds.

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

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

Example: A necklace made of beads, where each bead represents a monomer and the whole necklace is the polymer.

Formation and Breakdown of Polymers

Dehydration Synthesis

Polymers are formed by dehydration reactions (also called condensation reactions), where a water molecule is removed to form a new covalent bond between monomers.

• Dehydration Reaction: Joins two monomers by removing a water molecule.

Hydrolysis

Polymers are broken down into monomers by hydrolysis, a process in which a water molecule is added to break a covalent bond.

• Hydrolysis: Breaks a bond between monomers by adding a water molecule.

Classes of Biological Macromolecules

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with the formula (CH2O)n. They serve as energy sources and structural materials.

• Monosaccharides: Simple sugars (e.g., glucose, fructose) that are the monomers of carbohydrates.

• Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

Example: Starch (a polysaccharide) is a storage form of glucose in plants.

Proteins

Proteins are polymers of amino acids linked by peptide bonds. They perform a vast array of functions, including catalysis (enzymes), structure, transport, and signaling.

• Amino Acid: The monomer unit of proteins, consisting of a central carbon, amino group, carboxyl group, hydrogen atom, and variable R group.

• Polypeptide: A polymer of amino acids.

• Protein: One or more polypeptides folded into a specific three-dimensional structure.

Example: Alcohol dehydrogenase is an enzyme (protein) that catalyzes the breakdown of alcohol in cells.

Lipids

Lipids are a diverse group of hydrophobic molecules that are not true polymers. They include fats, phospholipids, and steroids.

• Fats (Triglycerides): Composed of glycerol and three fatty acids; used for long-term energy storage.

• Phospholipids: Major component of cell membranes, consisting of a glycerol backbone, two fatty acids, and a phosphate group.

• Steroids: Lipids with a structure of four fused rings (e.g., cholesterol, sex hormones).

Example: Phospholipids form the bilayer structure of cell membranes.

Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides that store, transmit, and help express genetic information.

• Nucleotide: The monomer of nucleic acids, consisting of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base.

• DNA (Deoxyribonucleic Acid): Stores genetic information.

• RNA (Ribonucleic Acid): Involved in gene expression and protein synthesis.

Example: DNA encodes the instructions for building proteins in all living organisms.

Summary Table: Macromolecules and Their Monomers