Biochem - Water, pH, Buffers

Why is the water molecule bent?

The water molecule is bent due to the two lone pairs of electrons on the oxygen atom, which repel the hydrogen atoms and create a bond angle of approximately 104.5 degrees.

Both CO₂ and H₂O have polar covalent bonds but only water is a polar molecule — why?

Water's bent shape causes an uneven distribution of charge, resulting in a dipole moment, while carbon dioxide is linear, leading to a balanced charge distribution.

H-Bonds

are weak attractions between the hydrogen atom of one molecule and the electronegative atom of another molecule, often occurring between water molecules.

• dominate water behavior

• bonds constantly break and reform

Why does ice float?

Ice floats because it is less dense than liquid water due to the hydrogen bonds creating an open hexagonal structure in ice.

• rigid hexagonal lattice

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Why is water an excellent solvent?

• Water is an excellent solvent due to polarity

• Hydration shells stabilize ions

• Ionic compounds dissociate (NaCl → Na⁺ + Cl⁻)

• Molecular compounds dissolve without dissociatin

When is water thermodynamically favorable?

When it is in disordered liquid state (High entropy)

What are the biological consequences if the hydrophobic effect?

The hydrophobic effect drives the aggregation of nonpolar molecules in aqueous solutions, leading to the formation of cellular membranes and the folding of proteins, which are crucial for biological function.

Amphiphilic/amphipathic

molecules contain both hydrophobic and hydrophilic regions, allowing them to interact with both water and lipids. This property is essential for the formation of cellular membranes.

Osmosis

• Passive movement of water across a semipermeable membrane

• Water moves toward higher solute concentration

Osmotic Pressure

Pressure required to stop water from diffusing through a membrane by osmosis

Hypotonic Solution

A solution with a lower solute concentration compared to another solution, causing water to move into cells, potentially leading to swelling or bursting.

Hypertonic Solution

A solution with a higher solute concentration compared to another solution, causing water to move out of cells, potentially leading to shrinkage.

Amphiprotic

Substances that can act as both an acid and a base, capable of donating or accepting protons depending on the pH of the environment.

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