Introduction to Biological Macromolecules and Chemical Reactions

Posted on Nov 3, 2024 in Chemistry

Biological Macromolecules

Monomers and Polymers

Biological macromolecules are large molecules that are essential for life. They are typically polymers, which are made up of repeating units called monomers. The number of monomers in a polymer determines its classification:

• Monomer: 1 part
• Dimer: 2 parts
• Trimer: 3 parts
• Oligomer: 4-10 parts
• Polymer: More than 10 parts

Examples of Biological Macromolecules

Proteins

Proteins are polymers of amino acids. When you eat protein, it is broken down into amino acids, which are then absorbed into your cells and reassembled to form your own proteins.

Protein Structure

Proteins have complex structures with four levels of organization:

1. Primary Structure: The sequence of amino acids.
2. Secondary Structure: Hydrogen bonding between the backbone atoms forms helices or sheets.
3. Tertiary Structure: Weak bonds between helices or sheets bend the polypeptide into a 3D structure.
4. Quaternary Structure: For proteins with multiple polypeptide chains, weak bonds between the chains determine the overall structure.

Examples of Proteins

• Myoglobin: An oxygen carrier in muscle with one polypeptide and a heme group containing iron.
• Hemoglobin: An oxygen carrier in blood with four polypeptides and four heme groups.

Types of Proteins

• Globular: Round and water-soluble (e.g., hemoglobin, myoglobin).
• Fibrous: Elongated and water-insoluble (e.g., keratin in hair, collagen in bones).

Protein Denaturation

Under certain conditions like high temperatures or acidic environments, proteins can lose their 3D structure (denature) and precipitate.

Functions of Proteins

• Enzymes (speed up reactions)
• Receptors (e.g., olfactory receptors, photoreceptors)
• Nutritional proteins
• Immune proteins
• Structural proteins

Carbohydrates

Carbohydrates, also known as sugars, have the general formula C₆H₁₂O₆ or C₆(H₂O)₆. They are classified as:

• Monosaccharides: Single sugars (e.g., glucose, fructose)
• Disaccharides: Double sugars (e.g., sucrose, maltose, lactose)
• Polysaccharides: Complex carbohydrates (e.g., starch, glycogen, cellulose)

Sweetness of Sugars and Sugar Substitutes

Chemical Reactions

Chemical reactions are represented by chemical equations:

Reactants -> Conditions -> Products

Types of Chemical Reactions

Synthesis or Combination

A + B -> AB

Example: C + O₂ -> CO₂

Degradation (Decomposition)

AB -> A + B

Example: H₂CO₃ -> CO₂ + H₂O

Single Displacement

AB + C -> CB + A

Example: 2Al + 3H₂SO₄ -> Al₂(SO₄)₃ + 3H₂

Double Displacement

AB + CD -> CB + AD

Example: AgNO₃ + HCl -> AgCl (precipitate) + HNO₃

Combustion (Burning)

CH₄ + 2O₂ -> CO₂ + 2H₂O

Condensation

C₂H₅OH + HO-C₂H₅ -> C₂H₅-O-C₂H₅ + H₂O

Hydrolysis

The opposite of condensation. Example: CH₃OCH₃ + HOH -> 2CH₃OH

Redox Reactions

Reduction and Oxidation

Reduction involves:

• Lowering of charge
• Addition of electrons
• Addition of hydrogen
• Removal of oxygen

Oxidation involves the opposite processes.

pH (Power of Hydrogen)

pH is a measure of acidity or basicity (alkalinity). The pH scale ranges from 0 to 14:

• Acidic: pH less than 7
• Neutral: pH equal to 7
• Basic: pH greater than 7

Example: Stomach acid (hydrochloric acid) is acidic.