Cell Bio: Chapter 5- Energy and Reactions

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Equilibrium

Rate of the forward reaction = Rate of the reverse reaction

Progress of Reaction

Reaction typically dominate in 1 direction

Ex: If initially more products are being produced when reaction reaches equilibrium there will be a higher concentration of products than reactants

K_eq (equilibrium constant)

The ratio of the concentration of product to the concentration of reactant

K_eq >1 then products are favored

0< K_eq <1 then reactants are favored

Equilibrium is determined by the laws of ___. What are the 1st and 2nd law

Thermodynamics

1st law: No energy is neither created nor destroyed but converted from one form to another

2nd law: With each reaction there is less energy available to do work and more energy is converted to less useful forms (law of entropy)

Gibb’s free energy equation

ΔG = ΔH - TΔS

ΔH = enthalpy

T = temperature (kelvin)

ΔS = entropy

ΔG =

G_products - G_reactants

If ΔG is negative then

• G_reactants > G_products

• Spontaneous

• Exergonic (energy is released)

• Ex: hydrolysis

If ΔG is positive then

• G_reactants < G_products

• Not Spontaneous

• Endergonic (energy is absorbed)

ΔG°’ = ΔG at what conditions

ΔG @ 1M R, 1M P, standard temperature and pressure, pH 7.0

What is the equation of G

G_R” = G_R°’ + RTln[R] & G_P” = G_P°’ + RTln[P]

To calculate ΔG then subtrate G_P and G_R = ΔG’ = ΔG°’ + RTln(Q)

What is the equation for ΔG°’

ΔG°’ = -RTlnK

__&___ directly impact ΔG

Concentration of products and concentrations of reactants

Most reactions are endergonic (+ΔG°’), how do cells overcome this?

• Regulate concentrations of R and P

  • Increasing conc of reactants and decreasing products, makes reaction spontaneous

• Input Energy

  • Coupling multiple reactions together can make reaction spontaenous