Chapter 5 - Macromolecules

Classes of Macromolecules

Biological macromolecules are large, complex molecules essential for life. They are classified into four major groups: carbohydrates, lipids, proteins, and nucleic acids. These molecules are typically polymers, made by linking smaller units called monomers.

• Monomers vs. Polymers: Monomers are small, repeating units; polymers are long chains of monomers.

• Dehydration Reaction: A chemical reaction that joins monomers by removing a water molecule.

• Hydrolysis: A reaction that breaks polymers into monomers by adding water.

• Example Equation:

Carbohydrates

Carbohydrates are the primary source of energy for cells and serve structural roles in organisms. They are classified based on the number of sugar units.

• Monosaccharides: Simple sugars such as glucose and fructose.

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

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

• Dehydration Synthesis Example: Formation of maltose from two glucose molecules:

Storage vs. Structural Polysaccharides

Polysaccharides serve as energy storage or structural components in cells.

• Storage Polysaccharides:

  • Starch: Energy storage in plants.

  • Glycogen: Energy storage in animals.

• Structural Polysaccharides:

  • Cellulose: Major component of plant cell walls.

  • Chitin: Found in the exoskeleton of arthropods and fungal cell walls.

Comparison Table:

Lipids

Lipids are hydrophobic molecules, mainly composed of hydrocarbons. They are not true polymers and serve as energy storage, structural components, and signaling molecules.

• Main Categories: Fats, phospholipids, steroids.

• Fats: Constructed from glycerol and three fatty acids, joined by ester linkages.

• Saturated vs. Unsaturated Fatty Acids:

  • Saturated: No double bonds; solid at room temperature.

  • Unsaturated: One or more double bonds; liquid at room temperature.

• Example Equation (Esterification):

Phospholipids

Phospholipids are major components of cell membranes. They consist of a phosphate group, glycerol, and two fatty acids, forming amphipathic molecules with hydrophilic heads and hydrophobic tails.

• Structure: Phosphate group + glycerol + 2 fatty acids.

• Function: Form bilayers in cell membranes and organelle membranes.

• Phospholipid Bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.

Example: The plasma membrane of cells is composed of a phospholipid bilayer.

Steroids

Steroids are lipids characterized by a carbon skeleton with four fused rings. They function as hormones and structural components.

• Examples: Cholesterol (membrane component), estradiol, testosterone (hormones).

• Functional Groups: Distinguish different steroids.

*Additional info: The notes continue with proteins, nucleic acids, and cell structure, but only the first part of the file is covered here. The content is highly relevant to General Biology, focusing on macromolecules and their biological roles.*