Macromolecules

Overview

Macromolecules are large, complex molecules essential for life, composed of smaller subunits. The four main classes—carbohydrates, lipids, proteins, and nucleic acids—play critical roles in cellular structure, function, and metabolism. Each class has unique monomers, bonding types, and biological functions.

Carbohydrates

Structure and Composition

• Elements: Carbon (C), Hydrogen (H), Oxygen (O)

• Monomer: Monosaccharide (simple sugars)

• Structural Features: Ring or linear carbon chain with hydroxyl (-OH) and carbonyl (C=O) groups

Types and Examples

• Monosaccharides: Glucose, fructose

• Disaccharides: Sucrose, lactose

• Polysaccharides: Starch, glycogen

Functions

• Provide fast cellular energy (especially glucose)

• Energy storage for later use (starch in plants, glycogen in animals)

• Build cell walls in plants (cellulose) and exoskeletons in insects (chitin)

Covalent Bond

• Glycosidic bond: Formed between two monosaccharides by a dehydration reaction

Example

• Glucose molecules join via glycosidic bonds to form starch or glycogen

Equation

Lipids

Structure and Composition

• Elements: Carbon (C), Hydrogen (H), Oxygen (O), sometimes Nitrogen (N) and Phosphorus (P)

• Monomer: No true monomers; structural units include glycerol and fatty acids

• Structural Features: Glycerol (3-carbon with -OH groups); Fatty acids (R-COOH)

Types and Examples

• Triglycerides: Vegetable oil (1 glycerol + 3 fatty acids)

• Phospholipids: Major component of cell membranes (phospholipid bilayer)

• Steroids: Cholesterol

• Waxes: Protective coatings on leaves

Functions

• Long-term energy storage (triglycerides)

• Structural component of cell membranes (phospholipids, cholesterol)

• Signaling molecules (steroids)

• Water retention (waxes)

• Thermal insulation (fats in animals)

Covalent Bond

• Ester linkage: Bond between fatty acid and glycerol formed by dehydration synthesis

Example

• Formation of a triglyceride: three fatty acids join one glycerol via ester linkages

Equation

Proteins

Structure and Composition

• Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), sometimes Sulfur (S)

• Monomer: Amino acid

• Structural Features: Central carbon atom bonded to amine group (R-NH2), carboxyl group (R-COOH), hydrogen atom, and variable R group

Types and Examples

• Enzymes: Lactase, amylase

• Structural proteins: Keratin, hemoglobin, antibodies

• Hormones/signaling proteins: Insulin, growth hormone

Functions

• Catalyze chemical reactions (enzymes)

• Build structures/tissues/muscles (structural proteins)

• Transport oxygen/nutrients (transport proteins)

• Cell signaling (hormones)

• Immune defense (defense proteins)

Covalent Bond

• Peptide bond: Formed by dehydration synthesis between carboxyl group of one amino acid and amino group of another

• Polymer of amino acids = polypeptide

Example

• Hemoglobin is a protein made of multiple polypeptide chains

Equation

Nucleic Acids

Structure and Composition

• Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P)

• Monomer: Nucleotide

• Structural Features: Nucleotide consists of a 5-carbon sugar (pentose), nitrogen-containing base, and 1-3 phosphate groups

Types and Examples

• DNA (Deoxyribonucleic acid): Unique genetic code, found in cell nuclei

• RNA (Ribonucleic acid): Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA)

Functions

• Storage and transmission of genetic information (DNA)

• Guiding protein synthesis (RNA)

• Transfer hereditary traits from parents to offspring

Covalent Bond

• Phosphodiester linkage: Phosphate group covalently bonds sugars of two nucleotides, forming the sugar-phosphate backbone

Example

• DNA is a polymer of nucleotides joined by phosphodiester bonds

Equation

Summary Table: Macromolecule Comparison