6'2 2 H2O2 2 H2O O2 EA18 kcalmol

1
6.2 2 H2O2 2 H2O O2
EA18 kcal/mol ferric ions EA13
kcal/mol catalase EA 7 kcal/mol a)
what does the activation energy diagram mean?
catalase is a more efficient catalyst for this
reaction than ferric ions because it reduces the
activation energy by a larger amount. This makes
the reaction more likely to proceed at a lower
temperature.
uncatalyzed ferrous ions catalase
energy
2
6.2 continued
b) name 2 properties of catalase that makes in a
more suitable intracellular catalyst than
platinum.
Catalase is an enzyme and can be easily
synthesized by cells. because catalase is an
enzyme, the reaction can be made more specific
than possible with ferric ions. Lastly, catalase
is a better catalyst.
c) how else might the reaction be accelerated?
Temperature might be increased, but enzymes in
the cell do not enjoy being boiled.
d) why is it advantageous for peroxide and
catalase to be compartmentalized in peroxisomes?
Compartmentalization protects the rest of the
cell from the reactive peroxide molecule.
Further, because peroxide is restricted to a
smaller area than the whole cell, the peroxide
is increased so catalase can act on it more
efficiently.
3
6.6 lactose water glucose
galactose
b gal
a. why is it important to say that the product
is negligible? If the product becomes
significant, then the reverse reaction can occur.
lactose rate lactose consumption 1 10 2 16.7 4
25 8 33.3 16 40 32 44.4
b. Michaelis-Menton plot
Doubling the S doesn't double the rate because
the enzyme reaction takes a certain amount of
time, which eventually becomes limiting.
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6.6 cont
c. Lineweaver-Burk plot
1/lactose 1/rate 1 0.10 0.5
0.062 0.25 0.04 0.125
0.03 0.063 0.025 0.031 0.023
d) what are Km and Vmax from the double
reciprocal plot?
1/Vmax y intercept .02 so Vmax 50
mmol/min -1/Km x intercept -.25 so Km 4.0
mM
e) half as much enzyme will give half as much
product per unit time ie. reaction velocity is
linearly dependent upon the amount of enzyme
5
6.7 enzyme kinetics a) what is Km of
galactokinase? Km tells the affinity of the
enzyme for its substrate. from the graph, -1/Km
-20 mM-1 so Km 1/20 mM 50 mM
b) what is Vmax? Vmax represents the initial
reaction velocity at the maximal S y intercept
1/Vmax 1/Vmax .1 Vmax 10 mmol/min
6
6.7 continued c) if ATP is varied and
galactose is high, what happens to Vmax? Vmax is
a property of the enzyme that depends on both
substrate concentrations. At saturating
conditions, substrate concentrations are not an
issue so Vmax should not change. The Km,
however, would be different and represent the
affinity of the enzyme for ATP, not galactose.
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6.8 CO2 H2O HCO3- H is
catalyzed by carbonic anhydrase kcat 1x106 per
second and a molecular weight of 30 kD
a) with 2 mg of pure enzyme and optimal
conditions, how many mmoles/ second of CO2 is
consumed?
2x10-6g/30000 g/mol 6.67 x 10-11 moles catalase
molecules each consumes 1x106 CO2/
second 6.67x10-111x106 6.67x10-5 moles CO2/
second .067 mmoles/sec
b) assuming standard temperature (298) and
pressure (1 atm) how many mL of carbon dioxide is
consumed per second?
PVnRT (ideal gas law) R gas constant 0.0821
Latm/Kmol V nRT/P V .067.0821298/1 V
1.63 mL per second