1.2 Chemical Foundations
Chemical Bonds in Biomolecules
Covalent Bonds
Strong bonds formed by sharing electrons
- ā¢ C-C bonds: ~350 kJ/mol
- ā¢ C-O bonds: ~360 kJ/mol
- ā¢ Phosphodiester bonds in DNA
- ā¢ Peptide bonds in proteins
Non-Covalent Bonds
Weaker but crucial for structure
- ā¢ Hydrogen bonds: ~20 kJ/mol
- ā¢ Ionic interactions: ~20 kJ/mol
- ā¢ Van der Waals: ~4 kJ/mol
- ā¢ Hydrophobic interactions
Hydrogen Bonding in DNA
A-T Base Pair
2 hydrogen bonds
Weaker pairing
G-C Base Pair
3 hydrogen bonds
Stronger pairing
Water and pH in Biology
Properties of Water
- Polarity: Enables dissolution of ionic and polar compounds
- Hydrogen bonding: High heat capacity, surface tension
- Cohesion: Important for transport in organisms
- Universal solvent: Medium for biochemical reactions
pH and Buffers
$$\text{pH} = -\log[H^+]$$
- ā¢ Physiological pH: 7.35-7.45 (blood)
- ā¢ Cellular pH: ~7.2
- ā¢ Stomach pH: 1.5-3.5
- ā¢ Buffers maintain pH homeostasis
Thermodynamics of Biomolecules
$$\Delta G = \Delta H - T\Delta S$$
Gibbs Free Energy Equation
ĪG < 0
Spontaneous (exergonic)
ĪG = 0
At equilibrium
ĪG > 0
Non-spontaneous (endergonic)
ATP hydrolysis: $\Delta GĀ°' = -30.5$ kJ/mol ā drives many cellular reactions
The Four Macromolecules
š§¬ Nucleic Acids
DNA and RNA - store genetic information
Monomers: Nucleotides
š¶ Proteins
Enzymes, structure, signaling
Monomers: Amino acids (20 standard)
š¬ Carbohydrates
Energy storage, structural support
Monomers: Monosaccharides
š§ Lipids
Membranes, energy, signaling
Not true polymers, diverse structures
Cellular Organization
Prokaryotes
- ā¢ No membrane-bound nucleus
- ā¢ Circular chromosome
- ā¢ 70S ribosomes
- ā¢ Examples: Bacteria, Archaea
Eukaryotes
- ā¢ Membrane-bound nucleus
- ā¢ Linear chromosomes
- ā¢ 80S ribosomes
- ā¢ Organelles (mitochondria, ER, etc.)