Lecture 1 - Structure, function, thermodynamics, hydrophobic effect

How do structures give rise to biological properties?

Energy changes (thermodynamics)

K_eq =

[products]/[reactants]

Low K_eq means…

Reactants > Products; product formation favored

High K_eq means…

Reactants < Products; reactant formation favored

Equilibrium means..

Concentrations are steady (not equal)

What determines if a reaction will or won’t proceed?

Thermodynamics

ΔG is..

Gibbs Free Energy, driving force of reactions

ΔG =

ΔH - TΔS

ΔG < 0 means..

The forward reaction will proceed spontaneously

Exergonic Reaction

Spontaneous, ΔG < 0

ΔG = 0 means..

System is at equilibirum

ΔG > 0 means..

The reaction will not proceed spontaneously, needs energy

Endergonic Reaction

Non-spontaneous (requiring energy), ΔG > 0

ΔH

Enthalpy change (heat)

ΔS

Entropy change (disorder)

Diffusion is..

Driven by entropy; molecules move from high to low concentration (spreading out → more entropy)

When ΔS is large…

ΔG is small (favorable)

When ΔS is small…

ΔG is large (not favorable)

ΔG^o

• Free energy change at standard conditions:

  • 298 K

  • 1 M of each reactant and product

Thermodynamic Coupling

A thermodynamically favorable reaction is used to drive a thermodynamically unfavorable reaction (when ΔG > 0)

Key role of water

Driving force in all biochemical reactions (mostly aqueous, structure depend on H₂O)

Water Properties

• Bent, high polarity

  • Dipole due to EN of oxygen

• 4 places to interact

Hydrogen bond

Weak electrostatic, attractive force that contributes to favorable enthalpy (ΔH)

Transient network

Hydrogen bonds constantly forming and breaking between water molecules

Hydrophobic Effect

Tendency for non-polar substances to group together due to being hydrophobic, leading to greater entropy in water molecules.

ΔS is maximized when…

Nonpolar substances group together in water (hydrophobic effect)