L I S T A 9
do wykładu dr. hab. inż. P. Dobryszyckiego
M e t a b o l i z m : p o d s t a w o w e p o j ę c i a i o r g a n i z a c j a
1. Which of the following is not a function or purpose of metabolism?
a) to extract chemical energy from substances obtained from the external environment b) to form and degrade the biomolecules of the cell
c) to convert exogenous foodstuffs into building blocks and precursors of macromolecules d) to equilibrate extracellular substances and the biomolecules of the cell e) to assemble the building-block molecules into macromolecules 2. If the ∆ G’ of the reaction A → B is –3.0 kcal/mol, which of the following statements are correct?
a) The reaction will proceed spontaneously from left to right at the given conditions.
b) The reaction will proceed spontaneously from right to left at standard conditions.
c) The equilibrium constant favors the formation of B over the formation of A.
d) The equilibrium constant could be calculated if the initial concentrations of A and B were known.
e) The value of standard free enthalpy change for this reaction is negative.
3. Glucose 1-phosphate is converted to fructose 6-phosphate in two successive reactions: Glucose-1-P → glucose-6-P
∆Gº′ = −1.7 kcal/mol
Glucose-6-P → fructose-6-P
∆Gº′ = −0.4 kcal/mol
What is ∆G°’ for the overall reaction?
a) −2.1 kcal/mol
b) −1.7 kcal/mol
c) −1.3 kcal/mol
d) 1.3 kcal/mol
e) 2.1 kcal/mol
4. The reaction:
phosphoenolpyruvate + ADP + H+ → pyruvate + ATP
has a ∆G°’ = −7.5 kcal/mol. Calculate ∆G°' for the hydrolysis of phosphoenolpyruvate.
5. Which of the following are ways by which two reactions can be coupled energetically to each other?
a) As common intracellular components of a compartment, two reactions become automatically coupled.
b) An ionic gradient across a membrane that is formed by one reaction can drive another reaction that uses the gradient to render it exergonic.
c) A shared, common intermediate can couple two reactions.
d) A protein that is activated by binding another molecule or by being covalently modified can provide energy to drive another reaction.
Lista 9 – M e t a b o l i z m : p o d s t a w o w e p o j ę c i a i o r g a n i z a c j a
- 1 z 2 -
6. ATP falls in the middle of the list of compounds having high phosphate group-transfer potentials.
Explain why this is advantageous for energy coupling during metabolism.
7. Under standard conditions, the free energy of hydrolysis of L-glycerol phosphate is −2.2 kcal/mol, and for ATP hydrolysis it is −7.3 kcal/mol. Show that when ATP is used as a phosphoryl donor for the formation of L-glycerol phosphate, the value of the equilibrium constant is altered by a factor of over 105.
8. Match the four cofactors in the left column with the appropriate structural features and properties from the right column.
a) ATP
(1)
nicotinamide ring
b) FAD
(2)
adenine group
c) NAD+
(3)
phosphoanydride bond
d) CoA
(4)
sulfur atom
e)
(5)
isoalloxazine ring
(6)
ribose group
(7)
acyl group transfer
(8)
electron transfer
(9)
phosphate transfer
9. ATP and NADH release large amounts of free energy upon the transfer of the phosphate group to H2O and electrons to O2, respectively. However, both molecules are relatively stable in the presence of H2O or O2. Explain why.
10. Which of the following are reasons the biochemical pathway for the catabolism of a molecule is almost never the same as the pathway for the biosynthesis of that molecule?
a) It would be extremely difficult to regulate the pathway if it served both functions.
b) The free-energy change would be unfavorable in one direction.
c) The reactions never take place in the same type of cell.
d) Enzyme-catalyzed reactions are irreversible.
e) Biochemical systems are usually at equilibrium.
11. Which of the following are ways by which metabolism is regulated?
a) accessibility of substrates
b) pressure fluxes
c) amounts of enzymes
d) control of enzyme activities
e) temperature cycles
Lista 9 – M e t a b o l i z m : p o d s t a w o w e p o j ę c i a i o r g a n i z a c j a
- 2 z 2 -