Solutes throw off a water molecule's "groove".

Fewer degrees of freedom means drop in entropy.

Drop in entropy makes the dissolving the compound less favorable.

$$\Delta G = \Delta H - T \color{red}{\Delta S}$$

Hydrophobic effect

Causes molecules to cluster together to maximize $\Delta S$

What happens when you create an amphipathic molecule (has both hydrophobic and hydrophilic character)?

Big idea: making molecules that are both hydrophilic and hydrophobic can give large-scale order

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Summary

• Biomolecules are built (mostly) from CHNOPS
• These atoms participate in covalent, ionic, hydrogen-bond, and van der Waals interactions
• Water can change the net strength of these interactions
• The "hydrophobic effect" works to minimize the amount of solute surface interacting with water
• Most biomolecules are "amphipathic," leading to self-organization
• The four main molecular building blocks (sugars, nucleic acids, amino acids, and lipids) differ in these properties allowing them to fulfill different roles

Tiny Molecules with Large Effects

2017-09-29

Thinking about the pH scale makes me feel:

The pH scale was invented by Søren Peder Lauritz Sørensen working at Carlsberg Labs

Conceptual goals

• Understand that how pH is measured and treated by biochemists.
• Understand how proton concentration can link to other equilibria to bring about molecular change.

Skill goals

• Reason about equilibria.
• Manipulate the Henderson-Hasselbalch equation and reason about the charge state of macromolecules in different pH regimes.

PROTONATION STATE IS NOT THE SAME AS CHARGE STATE!

Summary

A few protons can have a huge effect in biochemistry by linking to other equilibria.

Summary (continued)

The $pK_{a}$ is the $pH$ at which a titratable group is half-protonated.