Macromolecules and Their Biological Roles: General Biology Study Notes

Macromolecules in Biology

Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, proteins, nucleic acids, and lipids. They are formed by the polymerization of smaller units called monomers.

• Polymer: A long molecule consisting of many similar or identical building blocks linked by covalent bonds.

• Monomer: The repeating units that serve as building blocks for polymers.

• Enzymes: Specialized macromolecules that speed up chemical reactions.

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

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

Carbohydrates

Structure and Classification

Carbohydrates are sugars and polymers of sugars. They serve as fuel and building material for cells.

• Monosaccharides: The simplest carbohydrates, also known as simple sugars. Their molecular formula is usually a multiple of CH2O.

• Glucose (C6H12O6): The most common monosaccharide.

• Monosaccharides are classified by:

  • The location of the carbonyl group (as aldose or ketose).

  • The number of carbons in the carbon skeleton.

Disaccharides and Polysaccharides

Disaccharides are formed by joining two monosaccharides via a glycosidic linkage. Polysaccharides are polymers of sugars with storage and structural roles.

• Glycosidic linkage: Covalent bond between two monosaccharides.

• Storage polysaccharides: Starch (in plants), glycogen (in animals).

• Structural polysaccharides: Cellulose (in plants), chitin (in arthropods).

Comparison of Storage and Structural Polysaccharides

Type	Function	Location
Starch	Energy storage	Plants
Glycogen	Energy storage	Animals
Cellulose	Structural support	Plant cell walls
Chitin	Structural support	Exoskeletons of arthropods

Lipids

Types and Functions

Lipids are a diverse group of hydrophobic molecules that do not form polymers. Major types include fats, phospholipids, and steroids.

• Fats: Constructed from glycerol and fatty acids. Used for energy storage.

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

• Steroids: Lipids characterized by a carbon skeleton with four fused rings (e.g., cholesterol).

Fatty Acids

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

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

• Hydrogenation can convert unsaturated fats to saturated fats.

Comparison of Saturated and Unsaturated Fats

Type	Bond Type	State at Room Temp	Source
Saturated	No double bonds	Solid	Animal fats
Unsaturated	One or more double bonds	Liquid	Plant and fish fats

Proteins

Structure and Function

Proteins are polymers made of amino acids and perform a wide range of functions in cells, including catalysis, defense, transport, and structural support.

• Amino acids: Organic molecules with amino and carboxyl groups. There are 20 different amino acids.

• Polypeptide: A polymer of amino acids linked by peptide bonds.

• Protein: A functional molecule consisting of one or more polypeptides folded into a specific shape.

Levels of Protein Structure

• Primary structure: Sequence of amino acids.

• Secondary structure: Coils and folds (α helix, β pleated sheet) due to hydrogen bonding.

• Tertiary structure: Overall 3D shape due to interactions among side chains (R groups).

• Quaternary structure: Association of multiple polypeptides.

Protein Structure Table

Level	Description	Bond/Interaction
Primary	Sequence of amino acids	Peptide bonds
Secondary	α helix, β sheet	Hydrogen bonds
Tertiary	3D folding	R group interactions
Quaternary	Multiple polypeptides	Various interactions

Protein Denaturation

Denaturation is the loss of a protein's native structure due to changes in pH, temperature, or other environmental factors, often resulting in loss of function.

Nucleic Acids

DNA and RNA

Nucleic acids store and transmit hereditary information. The two types are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

• Nucleotide: The monomer of nucleic acids, consisting of a nitrogenous base, a pentose sugar, and one or more phosphate groups.

• Polynucleotide: A polymer of nucleotides.

Nitrogenous Bases

• Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U); single six-membered ring.

• Purines: Adenine (A) and Guanine (G); six-membered ring fused to a five-membered ring.

Base Pairing in DNA

• Adenine (A) pairs with Thymine (T)

• Guanine (G) pairs with Cytosine (C)

Gene Expression

DNA directs synthesis of messenger RNA (mRNA), which controls protein synthesis in a process called gene expression.

• Central Dogma: DNA → RNA → Protein

Summary Table: Nucleic Acids

Type	Sugar	Bases	Strands
DNA	Deoxyribose	A, T, C, G	Double
RNA	Ribose	A, U, C, G	Single

Additional info:

• Some context and definitions were expanded for clarity and completeness.

• Tables were inferred and reconstructed for comparison and classification purposes.