Macromolecules in Biology

Macromolecules are large, complex molecules essential for life. The four major classes are lipids, carbohydrates, proteins, and nucleic acids. Each class has unique monomers, polymers, bonds, and structural features.

Overview Table: Macromolecule Structure

Lipids

General Characteristics

• Lipids are diverse macromolecules without a consistent repeating monomer.

• They are hydrophobic due to many nonpolar covalent bonds.

Types and Functions

• Triglycerides: Main form of fat storage; composed of glycerol and three fatty acids.

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

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol, testosterone).

Fatty Acids

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

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

Functions

• Energy storage (triglycerides)

• Membrane structure (phospholipids)

• Signaling molecules (steroids)

Key Reactions

• Dehydration synthesis: Joins monomers by removing water to form polymers.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

Monosaccharides and Polysaccharides

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

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

Bond Formation

• Monosaccharides are joined by glycosidic bonds through dehydration synthesis.

Functions

• Primary function is energy storage (e.g., starch in plants, glycogen in animals).

• Structural support (e.g., cellulose in plant cell walls).

Nucleic Acids

Structure

• Nucleotides are the monomers, each consisting of a sugar, phosphate group, and nitrogenous base.

• Polymers are DNA and RNA.

• DNA sugar: deoxyribose; RNA sugar: ribose.

Nitrogenous Bases

• Pyrimidines: Cytosine, Thymine (DNA only), Uracil (RNA only).

• Purines: Adenine, Guanine.

Bonding and Polymerization

• Nucleotides are joined by phosphodiester bonds between the 5' and 3' carbons of the sugar.

• DNA is double-stranded; RNA is usually single-stranded.

Functions

• Information storage (DNA stores genetic information).

• RNA is involved in protein synthesis and gene regulation.

Proteins

Structure

• Monomer: Amino acid

• Polymer: Polypeptide

• Amino acids are linked by peptide bonds (covalent bonds).

Functions/Roles

• Enzymatic proteins: Catalyze chemical reactions (e.g., digestive enzymes).

• Defensive proteins: Protect against disease (e.g., antibodies).

• Storage proteins: Store amino acids (e.g., casein in milk).

• Transport proteins: Move substances (e.g., hemoglobin transports oxygen).

• Hormonal proteins: Coordinate organism activities (e.g., insulin regulates blood sugar).

• Receptor proteins: Respond to chemical stimuli.

• Contractile and motor proteins: Movement (e.g., actin and myosin in muscles).

Levels of Protein Structure

1. Primary structure: Sequence of amino acids in a polypeptide chain.

2. Secondary structure: Local folding into alpha-helices or beta-pleated sheets via hydrogen bonds.

3. Tertiary structure: Overall 3D shape due to interactions among R groups (hydrophobic interactions, van der Waals forces, ionic bonds, hydrogen bonds, covalent bonds).

4. Quaternary structure: Association of multiple polypeptide chains to form a functional protein.

Protein Structure and Function

• The structure of a protein determines its function.

• Proteins must fold correctly to perform their biological roles.

Protein Synthesis

• Amino acids are linked by peptide bonds to form polypeptides.

• Polypeptides fold into functional proteins.

Key Equations

• Dehydration synthesis:

• Hydrolysis:

Example: The enzyme amylase catalyzes the hydrolysis of starch (a polysaccharide) into glucose monomers, which can then be used for energy by cells.