Macromolecules: Structure, Function, and Biological Importance

Concept 5.1: Macromolecules are Polymers, Built from Monomers

Macromolecules (Polymers)

Macromolecules are large, complex molecules essential for life, formed by joining smaller units called monomers. The process of forming and breaking these polymers is fundamental to biological systems.

• Polymer: A long chain of monomers bonded together.

• Monomer: An individual unit that serves as the building block of a polymer.

• Dehydration Reaction: A chemical reaction that removes a water molecule to form a new bond between monomers. This process is called polymerization. $\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{dehydration}} \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis Reaction: A chemical reaction that adds water to break a bond, resulting in depolymerization. $\text{Polymer} + \text{H}_2\text{O} \xrightarrow{\text{hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Concept 5.2: Carbohydrates Serve as Fuel and Building Material

Carbohydrates (General Structure, Functions, and Examples)

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They are a primary source of energy and serve structural roles in cells.

• Monomers (Monosaccharides): Simple sugars that are the building blocks of carbohydrates.

  • Examples: Glucose, Galactose, Fructose

  • General formula: $\text{C}_6\text{H}_{12}\text{O}_6$ (for glucose)

• Structure/Glycosidic Linkage: Monosaccharides can join via glycosidic bonds to form disaccharides and polysaccharides.

  • Disaccharides: Two monosaccharides joined by a glycosidic linkage. Example: Maltose (glucose + glucose), Lactose (galactose + glucose).

  • Polysaccharides: Long chains of monosaccharides. Examples: Starch (energy storage in plants), Glycogen (energy storage in animals), Cellulose (structural component in plant cell walls).

Concept 5.3: Lipids are a Diverse Group of Hydrophobic Molecules

Lipids (General Structure, Functions, and Examples of Each Type)

Lipids are nonpolar molecules that are insoluble in water. They play key roles in energy storage, membrane structure, and signaling.

• General Properties:

  • Mostly hydrophobic; do not mix well with water.

  • May contain some polar bonds, but primarily consist of hydrocarbon regions.

  • Main function: energy storage (e.g., fats), insulation.

• Types of Lipids:

  1. Fats (Triacylglycerols):

     • Structure: One glycerol molecule joined to three fatty acids via ester linkages. $\text{Glycerol} + 3\ \text{Fatty Acids} \xrightarrow{\text{dehydration}} \text{Triacylglycerol} + 3\ \text{H}_2\text{O}$

     • Function: Long-term energy storage.

     • Saturated vs. Unsaturated Fatty Acids:

       • Saturated: No double bonds; molecules pack tightly, solid at room temperature.

       • Unsaturated: One or more double bonds; molecules cannot pack closely, liquid at room temperature.

  2. Phospholipids:

     • Structure: Phosphate head (hydrophilic) + two fatty acid tails (hydrophobic).

     • Function: Major component of cell membranes.

     • Form bilayers in aqueous environments, creating the basic structure of biological membranes.

  3. Steroids/Cholesterol:

     • Structure: Four fused carbon rings.

     • Function: Hormones (e.g., signaling molecules), membrane structure (cholesterol).

     • Example: Cholesterol is found in animal cell membranes and is a precursor for steroid hormones.

Type of Lipid	Structure	Main Function	Example
Fats (Triacylglycerols)	Glycerol + 3 Fatty Acids	Energy Storage	Butter, Oil
Phospholipids	Phosphate Head + 2 Fatty Acid Tails	Cell Membrane Structure	Phosphatidylcholine
Steroids	Four Fused Carbon Rings	Signaling, Membrane Structure	Cholesterol

Concept 5.4: Proteins Include a Diversity of Structures, Resulting in a Wide Range of Functions

Proteins (General Structure, Functions, and Examples)

Proteins are complex polymers made of amino acids. They perform a vast array of functions in living organisms, including catalysis, transport, structural support, and signaling.

• Functions:

  • Enzymes (speed up chemical reactions)

  • Defense (antibodies)

  • Storage (storage proteins)

  • Transport (transport proteins)

  • Cellular communication (hormones, receptors)

  • Movement (contractile proteins)

  • Structural support (collagen, keratin)

• Monomer: Amino Acid

  • Organic molecule with both an amino group ($-\text{NH}_2$) and a carboxyl group ($-\text{COOH}$).

  • Four different partners: amino group, carboxyl group, hydrogen atom, and variable R group.

• Polymerization:

  • Amino acids join via dehydration reactions, forming peptide bonds. $\text{Amino Acid}_1 + \text{Amino Acid}_2 \xrightarrow{\text{dehydration}} \text{Dipeptide} + \text{H}_2\text{O}$

• Levels of Protein Structure:

  1. Primary: Sequence of amino acids.

  2. Secondary: Local folding patterns (alpha helix, beta pleated sheet).

  3. Tertiary: Overall 3D shape, determined by interactions among R groups (basic, acidic, hydrophilic, hydrophobic).

  4. Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure due to environmental changes, resulting in loss of function.

Concept 5.5: Nucleic Acids Store, Transmit, and Help Express Hereditary Information

Nucleic Acids (Functions, General Structure, Examples)

Nucleic acids are polymers that store and transmit genetic information. The two main types are DNA and RNA.

• Functions:

  • Store genetic information (DNA)

  • Gene expression and protein synthesis (RNA)

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

• Polymerization: Nucleotides are joined by phosphodiester linkages. $\text{Nucleotide}_1 + \text{Nucleotide}_2 \xrightarrow{\text{dehydration}} \text{Dinucleotide} + \text{H}_2\text{O}$

• Examples: DNA (deoxyribonucleic acid), RNA (ribonucleic acid)

Type	Function	Monomer	Polymer Linkage
DNA	Genetic information storage	Nucleotide (deoxyribose)	Phosphodiester bond
RNA	Gene expression, protein synthesis	Nucleotide (ribose)	Phosphodiester bond

Additional info: These notes have been expanded for clarity and completeness, including definitions, examples, and academic context suitable for General Biology students.