Quick Chemistry of LIFE Notes

1. Ionic vs. Covalent Bonds

Ionic Bonds:

• Definition: Electrons are transferred between atoms, forming charged ions.
• Example: Sodium (Na) and Chlorine (Cl) → NaCl (table salt).
  • Sodium loses 1 electron (becomes Na⁺).
  • Chlorine gains 1 electron (becomes Cl⁻).
• Key Point: Atoms achieve stable electron shells (octet rule).
• Terminology:
  • Cation: Positively charged ion (e.g., Na⁺).
  • Anion: Negatively charged ion (e.g., Cl⁻).
• Polyatomic Ions: Groups like HCO₃⁻ (bicarbonate) act as single charged units.

Covalent Bonds:

• Definition: Electrons are shared between atoms.
• Example: H₂O (water) – oxygen shares electrons with hydrogen.
• Bond Representation: Lines (e.g., H–O–H) denote shared electron pairs.
• Key Point: Common in biological molecules (proteins, DNA, etc.).
• Atoms Involved: CHONP (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus) – the “big five” in human biology.

Tip:

• Ionic = metals + nonmetals (charged).
• Covalent = nonmetals (shared electrons).

2. Polar vs. Nonpolar Molecules

Polar Molecules:

• Definition: Uneven electron sharing → partial charges (e.g., water: H₂O).
  • Oxygen is electronegative, pulling electrons closer → slight negative charge (δ⁻).
  • Hydrogens have slight positive charges (δ⁺).
• Biological Importance:
  • Water’s polarity enables dissolving salts, forming hydration shells.
  • Drives hydrophobic/hydrophilic interactions (e.g., cell membranes).

Nonpolar Molecules:

• Definition: Equal electron sharing → no partial charges (e.g., lipids, O₂).
• Role: Hydrophobic; aggregate away from water (e.g., cell membrane tails).

3. Chemical Reactions & Enzymes

Reaction Types (Simplified):

1. Anabolic: Build molecules (requires energy).
   • Example: Protein synthesis.
2. Catabolic: Break molecules (releases energy).
   • Example: Glucose breakdown in cellular respiration.

Enzymes:

• Function: Biological catalysts that lower activation energy.
• Example: ATP synthase (creates ATP).

4. Cellular Respiration & ATP

• ATP (Adenosine Triphosphate):
  • Not energy itself, but stores energy in phosphate bonds.
  • Breaking ATP → ADP + Pᵢ releases energy for cellular work.
• Cellular Respiration:
  • Glucose + O₂ → CO₂ + H₂O + ATP (via glycolysis, Krebs cycle, ETC).

5. Acids and Bases

• Acids: Release H⁺ ions (proton donors; pH < 7).
• Bases: Accept H⁺ ions (proton acceptors; pH > 7).
• Biological Relevance:
  • Blood pH (~7.4) tightly regulated by buffers (e.g., bicarbonate).

Takeaways

• Ionic bonds = electron transfer (salts); covalent bonds = electron sharing (organic molecules).
• Water’s polarity is vital for life (solvent, transport, temperature regulation).
• ATP fuels cellular processes by releasing energy when broken.
• Enzymes speed up reactions without being consumed.

Study Tip: Focus on how these concepts apply to human physiology (e.g., nerve impulses rely on ion gradients; enzymes digest food).