The Structure and Function of Macromolecules (Chapter 5) – Study Notes

Macromolecules

Definition and Overview

Macromolecules are large, complex molecules essential to life, composed of thousands of atoms or more. They are typically formed by the polymerization of smaller subunits called monomers.

• Macromolecules: Large molecules necessary for various biological functions.

• Polymers: Large molecules made up of repeating subunits (monomers) linked together.

• Monomers: The small, repeating units that serve as the building blocks of polymers.

Polymerization Reactions

• Condensation Synthesis (Dehydration Synthesis): A chemical reaction in which two monomers are joined together by removing a molecule of water. This process builds polymers from monomers.

• Hydrolysis: The process of breaking down polymers into monomers by adding water, which separates the subunits.

Example: The breakdown of starch (a polymer) into glucose (a monomer) during digestion involves hydrolysis.

Carbohydrates

Structure and Types

Carbohydrates are organic molecules consisting of carbon, hydrogen, and oxygen, typically with a hydrogen:oxygen atom ratio of 2:1. They serve as energy sources and structural components in cells.

• Monosaccharides: The simplest carbohydrates (simple sugars) with the general formula $C_nH_{2n}O_n$. Example: Glucose ($C_6H_{12}O_6$).

• Disaccharides: Formed by joining two monosaccharides via a glycosidic linkage. Example: Sucrose (glucose + fructose).

• Polysaccharides: Long chains of monosaccharides. They can be storage forms (e.g., starch in plants, glycogen in animals) or structural (e.g., cellulose in plant cell walls).

Examples of Monosaccharides

• Glucose

• Galactose

• Fructose

Each of these sugars has the same molecular formula ($C_6H_{12}O_6$) but different structural arrangements (isomers).

Examples of Disaccharides

• Maltose: Glucose + Glucose

• Lactose: Glucose + Galactose

• Sucrose: Glucose + Fructose

Polysaccharides Table

Type	Example	Function
Storage	Starch (plants), Glycogen (animals)	Energy storage
Structural	Cellulose (plants)	Cell wall structure

Lipids

Structure and Types

Lipids are a diverse group of hydrophobic molecules, commonly known as fats. They are composed mainly of carbon, hydrogen, and oxygen, but with a much lower proportion of oxygen than carbohydrates.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group at one end. Can be saturated (no double bonds) or unsaturated (one or more double bonds).

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

• Steroids: Lipids with a structure of four fused carbon rings. Example: Cholesterol, testosterone, estradiol.

Function: Lipids are important for long-term energy storage, insulation, and as structural components of cell membranes.

Example of a Saturated Fatty Acid Structure

• Straight hydrocarbon chain with single bonds between carbons.

• Solid at room temperature (e.g., butter).

Comparison of Lipid Types

Lipid Type	Structure	Function
Fatty Acid	Long hydrocarbon chain, carboxyl group	Energy storage
Phospholipid	Glycerol, 2 fatty acids, phosphate group	Cell membrane structure
Steroid	Four fused carbon rings	Hormones, membrane component

Additional info: Lipids are not true polymers because they are not made from repeating monomer units in the same way as carbohydrates, proteins, and nucleic acids.