NADH is the primary electron and oxygen is the terminal electron acceptor in the aerobic

membrane bound electron transport chain. The overall electron transfer reactions can be

described by the reaction

2 NADH + 2H+ + O2 --> 2 NAD+ + 2 H2O

If the above reaction takes place in an aqueous solution at pH 7.6, at 25o C, with the

following steady state product and substrate concentrations: [NAD+] = 20.0 mM, [NADH]

= 10.0 mM, and oxygen at a partial pressure of 100.0 torr, calculate the free-energy change

for this oxidation of NADH by oxygen. The standard state for a gas is a pressure of 1 atm

or 760 torr. The biochemical standard state for hydrogen ion is pH 7, or 10-7 M. The

universal gas constant is 8.314472 J K-1mol-1. Standard Gibbs free energy change at pH 7.6

and 25 o C for the above reaction is -220.3 kJ mol-1. Zero degrees Celsius is equivalent to

273.15 degrees Kelvin.

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Question 2 on next page

Question 2. [10 marks]

A new strain of yeast is being considered for biomass production in a chemostat reactor.

2a) Sketch a typical chemostat reactor, and by using a simple material balance on the

limiting substrate in the absence of endogenous metabolism given as;

, prove that

where is the maintenance coefficient based on substrate S, is the

apparent yield, while is a constant.

2b) The following data were obtained using the reactor and the proven equation in (a)

above. An influent substrate concentration of 800 mg/L and an excess of oxygen were

used at a pH of 5.5 and T = 350C. Using the following data, calculate m, Ks, M

X S Y / , kd, and

ms, assuming d

net k

K S









Dilution

rate (h-1)

Carbon substrate

concentration (mg/L)

Cell concentration

(mg/L)

0.1 16.7 366

0.2 33.5 407

0.3 59.4 408

0.4 101 404

0.5 169 371

0.6 298 299

0.7 702 59

V q X

FS FS V X R

P S

M R P

X S

R g    

/ /

1 1



Y Y

X S

 

/ /

1 1

X S

s Y

 AP

X S Y /

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