Macromolecules

Introduction to Macromolecules

Macromolecules are large, complex molecules that are fundamental to the structure and function of living cells. They are typically formed by the polymerization of smaller subunits called monomers, which are linked together by covalent bonds.

• Definition: A macromolecule is a large molecule composed of thousands of atoms, usually by the assembly of repeating monomer units.

• Examples: Carbohydrates, lipids, proteins, and nucleic acids.

• Polymerization: The process by which monomers are chemically bonded to form polymers.

• Importance: Macromolecules are essential for cellular structure, function, and information storage.

Polymer Formation and Breakdown

• Dehydration Synthesis (Condensation Reaction): Monomers are joined together by covalent bonds through the removal of a water molecule. This process requires energy input.

• Hydrolysis: Polymers are broken down into monomers by the addition of water, releasing energy.

• General Equation for Dehydration Synthesis:

• General Equation for Hydrolysis:

Types of Biological Macromolecules

The four major classes of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids. Each class has distinct structures, monomers, bonds, and functions.

Carbohydrates

Structure and Types

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

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

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (e.g., maltose, sucrose).

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

Monosaccharide Classification

• Aldose: Monosaccharide with an aldehyde group (e.g., glucose, ribose).

• Ketose: Monosaccharide with a ketone group (e.g., fructose, ribulose).

• Trioses, Pentoses, Hexoses: Classified by the number of carbons (3, 5, 6, respectively).

Polysaccharide Functions and Examples

• Starch: Energy storage in plants; composed of α-glucose monomers.

• Glycogen: Energy storage in animals; highly branched polymer of glucose.

• Cellulose: Structural component of plant cell walls; composed of β-glucose monomers.

• Chitin: Structural polysaccharide in fungal cell walls and arthropod exoskeletons.

• Peptidoglycan: Structural polysaccharide in bacterial cell walls.

Comparison of Major Polysaccharides

Lipids

Structure and Types

Lipids are hydrophobic molecules that include fats, oils, phospholipids, and steroids. They are not true polymers but are assembled from smaller molecules by dehydration synthesis.

• Triglycerides: Composed of glycerol and three fatty acids; used for long-term energy storage.

• Phospholipids: Glycerol, two fatty acids, and a phosphate group; major component of cell membranes.

• Steroids: Four fused hydrocarbon rings; includes cholesterol and hormones.

Fatty Acids

• Saturated Fatty Acids: No double bonds; solid at room temperature; found in animal fats.

• Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature; found in plant oils.

• Cis vs. Trans Fats: Cis double bonds create kinks, preventing tight packing; Trans fats are artificially hydrogenated and can contribute to cardiovascular disease.

Functions of Lipids

• Long-term energy storage

• Insulation and protection

• Major component of cell membranes (phospholipids)

• Hormone synthesis (steroids)

Nucleic Acids

Structure and Function

Nucleic acids store and transmit genetic information. They are polymers of nucleotides, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA (Deoxyribonucleic Acid): Double-stranded helix; stores genetic information.

• RNA (Ribonucleic Acid): Single-stranded; involved in protein synthesis and gene regulation.

• ATP (Adenosine Triphosphate): Energy currency of the cell.

Nucleotide Structure

• Pentose sugar (ribose in RNA, deoxyribose in DNA)

• Phosphate group

• Nitrogenous base (A, T, G, C in DNA; A, U, G, C in RNA)

Phosphodiester Bond Formation

Nucleotides are joined by phosphodiester bonds between the 3' hydroxyl of one sugar and the 5' phosphate of the next.

Base Pairing in DNA

• Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds.

• Guanine (G) pairs with Cytosine (C) via 3 hydrogen bonds.

Proteins

Structure and Function

Proteins are polymers of amino acids linked by peptide bonds. They perform a vast array of functions in the cell, including catalysis, structure, transport, and signaling.

• Monomer: Amino acid (20 standard types)

• Polymer: Polypeptide

• Bond: Peptide bond (formed by dehydration synthesis)

• Functions: Enzymes, structural support, transport, storage, communication, movement, defense

Levels of Protein Structure

• Primary Structure: Linear sequence of amino acids.

• Secondary Structure: Local folding into α-helices and β-pleated sheets, stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape of a polypeptide, determined by interactions among R groups.

• Quaternary Structure: Association of multiple polypeptide chains (subunits) into a functional protein.

Protein Function and Shape

• Protein function is determined by its shape; changes in shape (denaturation) can lead to loss of function.

• Examples: Hemoglobin (oxygen transport), enzymes (catalysis), antibodies (defense).

Summary Table: Macromolecule Comparison

Additional info: Some content, such as chemical structures and diagrams, was inferred and expanded for clarity and completeness. The notes are organized to provide a comprehensive overview suitable for college-level General Biology students.