General Biology I: Biological Macromolecules – Structure, Function, and Types

Biological Macromolecules

Introduction to Macromolecules

Biological macromolecules are large, complex molecules essential for life. They include carbohydrates, lipids, proteins, and nucleic acids, each with unique structures and functions in living organisms.

• Macromolecules are polymers built from smaller subunits called monomers.

• They are responsible for most of the structure and function of cells.

• Examples: Starch (carbohydrate), Triglycerides (lipid), Hemoglobin (protein), DNA (nucleic acid).

Chemical Reactions in Biology

Basic Principles

Chemical reactions are fundamental to the synthesis and breakdown of macromolecules in living systems.

• Chemical reactions rearrange matter but do not create or destroy it (Law of Conservation of Mass).

• Reactants are transformed into products through the making and breaking of chemical bonds.

• Example: Cellular respiration

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$

Organic Macromolecules

Types and General Properties

Living organisms are composed of four main types of carbon-based macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

• Each type has a unique structure and function.

• Most are polymers, assembled by joining monomers through dehydration (condensation) reactions and broken down by hydrolysis reactions.

Lipids

Fatty Acids

Lipids are hydrophobic molecules that include fats, oils, phospholipids, steroids, and waxes. Fatty acids are the building blocks of many lipids.

• Fatty acids consist of a hydrocarbon chain with a carboxyl group at one end.

• They can be saturated (no double bonds, straight chains, solid at room temperature) or unsaturated (one or more double bonds, kinked chains, liquid at room temperature).

Lipid Types

• Triglycerides: Composed of three fatty acids linked to glycerol; main function is energy storage.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails, forming bilayers.

• Steroids: Characterized by four fused carbon rings; include hormones like cholesterol.

• Waxes: Long-chain fatty acids esterified to long-chain alcohols; provide protective coatings.

Table: Comparison of Lipid Types

Lipid Type	Structure	Main Function
Triglyceride	Glycerol + 3 fatty acids	Energy storage
Phospholipid	Glycerol + 2 fatty acids + phosphate group	Membrane structure
Steroid	Four fused carbon rings	Hormones, membrane component
Wax	Long-chain fatty acid + alcohol	Protection, waterproofing

Carbohydrates

Functions

Carbohydrates are essential for energy storage, structural support, and cell recognition.

• Serve as fuel for cellular activities (e.g., glucose metabolism).

• Provide structural material in plants (cellulose) and animals (chitin).

• Play a role in cell identity and signaling (glycoproteins, glycolipids).

Classification

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

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

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

Monosaccharides

• Basic formula: $C_nH_{2n}O_n$ (e.g., glucose: $C_6H_{12}O_6$).

• Can exist in linear or ring forms.

• Spatial arrangement of atoms determines properties (e.g., glucose vs. galactose).

Polysaccharides

• Polymers of monosaccharides linked by glycosidic bonds.

• Examples:

  • Starch: Energy storage in plants.

  • Glycogen: Energy storage in animals.

  • Cellulose: Structural support in plant cell walls.

Table: Major Polysaccharides and Their Functions

Polysaccharide	Monomer	Function	Location
Starch	Glucose	Energy storage	Plants
Glycogen	Glucose	Energy storage	Animals
Cellulose	Glucose	Structural support	Plant cell walls

Proteins

Structure and Function

Proteins are polymers of amino acids and perform a vast array of functions in cells, including catalysis, structure, transport, and signaling.

• Amino acids are the monomers of proteins, each containing a central carbon, amino group, carboxyl group, hydrogen atom, and variable R group.

• Proteins have four levels of structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet).

  • Tertiary: Overall 3D shape.

  • Quaternary: Association of multiple polypeptides.

• Protein shape determines function; denaturation can disrupt activity.

Table: Levels of Protein Structure

Level	Description	Example
Primary	Linear sequence of amino acids	Insulin polypeptide chain
Secondary	α-helix or β-sheet folding	Keratin (α-helix)
Tertiary	3D folding of a single polypeptide	Myoglobin
Quaternary	Multiple polypeptides assembled	Hemoglobin

Summary

• Macromolecules are essential for life, each with distinct structures and functions.

• Chemical reactions such as dehydration and hydrolysis are key to their synthesis and breakdown.

• Understanding the properties of carbohydrates, lipids, and proteins is fundamental to biology.