Lecture on Water in Biochemistry

Importance of Water

• Essential in biochemistry; often overlooked as inorganic.
• Solvent for many chemical reactions in living systems.
• Unique due to its molecular structure (H₂O).

Molecular Structure of Water

• Composed of one oxygen and two hydrogen atoms.
• Oxygen is electronegative, attracts electrons more strongly than hydrogen.
• Creates a charge differential: partial negative on oxygen, partial positive on hydrogen.
• Enables hydrogen bonding between water molecules.

Hydrogen Bonding

• Water molecules attract each other via hydrogen bonds.
• Although weaker than covalent or ionic bonds, they provide 'stickiness' to water molecules.
• Responsible for water's surface tension.

Comparative Example: Oil

• Oil molecules exhibit nonpolar interactions (Van der Waals forces) leading to weak attraction and spreading.
• Contrasts with water which forms beads due to hydrogen bonding.

Specific Heat Capacity of Water

• High energy required to change water from liquid to gas due to hydrogen bonds.
• Water remains liquid at room temperature unlike similar molecules (e.g., methane).
• Specific heat capacity helps stabilize Earth’s temperature.
  • Oceans absorb and release heat, acting as a temperature buffer.

Water's Role in Earth's Climate

• Stabilizes global temperatures, contributing to a temperate climate.
• Life thrives due to consistent environmental conditions.
• Search for life on other planets often begins with searching for water.

Phase Changes and Ice

• Uniquely, ice floats on water.
• Crystal formation in ice spaces water molecules further apart, making ice less dense.
• Important for life; prevents oceans from freezing solid.

Water as a Solvent

• Dissolves various molecules due to polarity.
• Example: Sodium chloride (NaCl) dissolves as water forms hydration shells around ions.
• Water dissolves proteins, carbohydrates, like glucose.

Cartoon Illustration

• Cartoon shows NaCl dissolving in water, forming hydration shells.
• Demonstrates water's role as a solvent visually.

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Next Topic

• Discussion will continue on organic molecules.