Wk1L1 Lecture 1 flashcards

Introduction to Biochemistry

• Welcome and Context

  • Instructor: Jerome Lenos, Structural Biologist at Monash University

  • Course: Biochemistry for BMS1021

  • Focus of Lecture: Chemical composition of cells, especially water, lipids, and nucleic acids.

Chemical Composition of Cells

• Major Components of the Human Body

  • 60% Water: Essential for cellular function

  • 15% Lipids: Vital for energy storage

  • 15% Proteins: Critical for cellular architecture

  • 1% Carbohydrates: Minor but necessary

Importance of Water

• Key Characteristics of Water:

  • Abundant: 75% of Earth's surface and ~0.02% of the Earth's mass.

  • Molecular Interactions: Focus on intra and intermolecular bonding.

  • Biological Importance: Physical and chemical properties of water affecting cellular processes.

Learning Objectives

• Describe water's structure, geometry, and polarity.

• Explain how hydrogen bonds contribute to water's properties:

  • Cohesion

  • High heat capacity

  • Boiling point

  • Density

  • Solvent properties

• Understand ionization of water and pH's impact on biological molecules.

Properties of Water

• Molecular Representation:

  • Various representations in textbooks: molecular formula (H2O), structural formulas, space-filling models.

  • Polar Nature:

    • Oxygen is partially negatively charged; hydrogens are partially positively charged.

• Hydrogen Bonding:

  • Water forms hydrogen bonds, creating networks with neighboring molecules.

  • Each water molecule can form up to four hydrogen bonds.

  • Hydrogen bonds are weaker than covalent bonds (20x weaker).

Unique Properties of Water

• Cohesion:

  • Water molecules attract each other, forming larger droplets (e.g., on a glass surface).

  • Capillary action: Water rising in narrow tubes relates to cohesion.

  • Surface tension: Allows insects to walk on water.

• High Heat Capacity:

  • Requires significant energy to change temperature due to hydrogen bonds breaking.

  • Defined as the energy needed to raise 1g of water by 1°C.

• Boiling Point & Heat of Vaporization:

  • High heat of vaporization (2000+ kJ/kg) due to hydrogen bonds needing to break for evaporation.

• Density and Ice Formation:

  • Unusual behavior: Ice is less dense than liquid water, allowing it to float.

  • Stability of hydrogen bonds in ice leads to expanded structure.

• Water as a Solvent:

  • Excellent solvent for ionic compounds (e.g., sodium chloride).

  • Interactions between water and ions lead to solubility.

  • Polar and non-polar interactions: Water cannot dissolve hydrophobic molecules like oils.

Ionization and pH of Water

• Ionization:

  • Water can ionize to form protons (H+) and hydroxyl ions (OH-).

  • At equilibrium (25°C), concentrations of H3O+ and OH- are equal (1 x 10^-7 M).

• Effect of Solutes on pH:

  • Adding acids/bases shifts concentrations of ions, altering pH.

  • Common pH examples:

    • Ammonia/bleach (high pH), gastric juice (low pH), distilled water (neutral pH of 7).

Impact of pH on Biological Molecules

• pH and Amino Acids:

  • pH affects the charge of amino acids (e.g., alanine has different forms at different pH levels).

  • pKa values represent the pH at which a molecule exists in equal parts.

  • Importance of pI (isoelectric point) where net charge is zero for amino acids.

• Enzymatic Activity:

  • Enzymes have optimal pH for activity influenced by the amino acid composition.

  • Changes in pH can denature proteins and affect structure and function.

Buffer Systems

• Definition:

  • Mixtures of weak acids and conjugate bases that resist pH changes.

• Function:

  • Buffers can absorb excess protons or hydroxide ions, maintaining equilibrium and pH stability in biological systems.

Summary of Water Properties

• Water is a polar molecule forming hydrogen bonds and ionizing properties.

• It exhibits unique macroscopic and cellular properties due to these characteristics, affecting biological processes.

Overview of Lipids and Nucleic Acids

• Lipids

  • Diverse, primarily hydrophobic, include triglycerides (energy storage), phospholipids (membrane structure), and other types (steroids, vitamins).

• Nucleic Acids

  • DNA and RNA as polymers of nucleotides, crucial for genetic information and protein synthesis.

  • Structure of DNA: double-stranded, formed through complementary bases (A-T, G-C), held together by hydrogen bonds.

  • Importance of nucleic acids: their sequence determines the genetic code and function.

Conclusion

• Lecture wraps up with the reminder of the biological significance of these molecules and leads into Lecture 2, focusing on carbohydrates and proteins.