Chapter 6 - Enzyme kinetics and thermodynamics

Enzymes bind ___ with low-affinity and ___ with high-affinity

products, substrates

First law of thermodynamics

energy is neither created nor destroyed. It can be changed/transformed from one form to another i.e. chemical, electrical, motion, light, heat, etc.

Second law of thermodynamics

Gibb’s free energy (G), entropy (S), and enthalpy (H)

No energy transformation is 100% complete; some energy is always lost to disorder (entropy)

Equation for second law of thermodynamics (in any closed system)

Total energy (enthalpy) = usable/free energy (G) + unusable energy (entropy)

H = G + TS

(T = absolute temperature)

Exergonic reaction

releases free energy; -deltaG (deltaG < 0)

spontaneous

Endergonic reaction

requires free energy; +deltaG (deltaG > 0)

If deltaG = 0, the reaction is at ___

equilibrium

Coupling ___ to an endergonic reaction makes the total reaction favorable

ATP Hydrolysis

How do enzymes act?

reduce activation energy of rxn, speed up rate of rxn

What DON’T enzymes do?

change the free energy of a rxn, alter rxn equilibrium

How do enzymes lower the activation energy?

Brings substrate to binding site, stabilizes transition state (can temporarily add chemical groups to substrates, sometimes make/break covalent bonds in process)

Competitive inhibitor

reversible or irreversible inhibitor; prevents substrate binding by binding enzyme at active site

no catalysis

Allosteric inhibitor

binds enzyme at different site (not active site) → active site changes shape so substrate cannot bind

no catalysis

Allosteric activator

binds to allosteric site → active site is correct shape so substrate can bind it