Lecture 2: Chemical Bonding and Molecular Interactions; Lipids and Membranes

Overview

• Introduction to molecules of life and non-covalent interactions.
• Focus on lipids and membranes; importance of chemical bonding.
• Dimensions and units: Angstroms as a common unit in biochemistry.

Chemical Bonding

• Covalent Bonds: Important for structure; strong and permanent.
• Non-covalent Bonds: Weak, dynamic, essential for biological processes like DNA structure and protein folding.
• Energy of covalent bonds: ~90-100 kcal/mol; non-covalent bonds: 1-10 kcal/mol.

Units of Measurement

• Angstrom: Commonly used in biochemistry; 10 Å = 1 nm.
• Engineers use micrometers and nanometers.

Molecules of Life

• Carbohydrates: Energy storage, signaling, structural roles.
• Amino Acids & Nucleosides: Building blocks for proteins and nucleic acids.
• Phospholipids: Form micelles and lipid bilayers; crucial for cell boundaries.

Chemical Interactions

• Covalent vs Non-covalent: Structure vs Dynamics.
• Non-covalent Forces:
  • Ionic bonds (Salt bridges)
  • Hydrogen bonds
  • Hydrophobic interactions
  • van der Waals forces

Biological Macromolecules

• Composed mainly of six elements: H, C, N, O, P, S.
• Critical components: Metal ions like Na, Mg, K, Ca.

Functional Groups

• Hydroxyl
• Carboxyl & Carboxylate
• Amino
• Phosphate
• Sulfhydryl (Thiol)
• Composite groups: Amide, Ester, Phosphate Ester

Lipids

• Characteristics: Rich in C-H and C-C bonds; hydrophobic nature.
• Types:
  • Triglycerides: Energy storage.
  • Phospholipids: Form cell membranes.
  • Steroids: Hormonal roles.
• Lipid Importance: Energy storage, signaling, component of membranes.

Membrane Structure

• Lipid Bilayer: Forms cell membranes; semi-permeable.
• Supramolecular Structures: Self-assembly into micelles, liposomes, bilayers.
• Evolutionary importance: Lipid bilayers enable cellular compartmentalization.

Health Implications

• Trans Fats: Increase low-density lipoproteins, contributing to heart disease.
• Cis Fats: Considered healthier, found in natural oils.

Concluding Points

• Next class will cover amino acids, peptides, and proteins.
• Recommended reading: Section 3.2 in the textbook.

These notes summarize the key points discussed in the lecture, providing a foundational understanding of chemical bonding, molecular interactions, and the critical roles of lipids and membranes in biology.