For a chemical reaction, K_eq = 0.73. Which of the following can you conclude ab

Question

For a chemical reaction, K_eq = 0.73. Which of the following can you conclude about this reaction? Do not use any formulas or calculations to determine your answer. (Select all that apply) a. Delta G degree' = 0 _____ b. The reaction is exergonic _____ c. The value of Delta G degree' is positive _____ d. This reaction could not go in the forward direction under physiologic conditions _____ e. This reaction could go in the forward direction under physiologic conditions _____ Answer the following true of false questions about regulation of enzyme activity. a. The binding of an allosteric effector to an enzyme is reversible. T or F b. Regulation of enzyme activity by covalent modification is reversible. T or F c. Allosteric regulation may increase or decrease enzyme activity. T or F d. Regulation of enzyme activity by covalent modification may increase or decrease enzyme activity. T or F e. Allosteric regulation requires the activity of another, "regulatory" enzyme. T or F f. Regulation by covalent modification requires the activity of another, "regulatory" enzyme. T or F

Explanation / Answer

Ans. #3.          dG0’ = - RT lnK        - equation 1

            Where,

                        dG0’ = Standard Gibb's free energy

                        R = Universal gas constant = 0.008315 kJ mol-1 K-1

T = Temperature in kelvin

K = Equilibrium constant

Note than the value of (ln Keq) is always a negative value if keq is less than 1. Or, because the value of (ln X) is always negative for X = less than 1.

So, ln Keq = ln (0.73) = - 0.314

If we put the value of lnK in equation 1,

            dG0’ = - RT (- 0.314) = + 0.314 RT

Therefore, if Keq is smaller than 1, then dG0’ will become Positive. A reaction with positive dG0’ value is non-spontaneous under standard physiological conditions. Note that a reaction with negative dG0’ value is spontaneous.

Thus, correct options are: C. The value of dG0’ is positive.

            D. The reaction could NOT go …

Note that spontaneity of a reaction can’t directly be correlated with enthalpy (endergonic or exergonic nature) of reaction. So, option B can’t be correlated.

#3. A. True. All allosteric modulators, for example ATP for phosphofructokinase I (PFK I) enzyme of glycolysis, bind reversibly to the enzyme.

#B. True. Covalent modifications, like phosphorylation and dephosphorylation, are generally reversible.

#C. True. It depends on the relative concentration of allosteric modulators.

For example, a high ATP/ AMP ratio decreases the activity of PFK1. A high AMP/ ATP ratio increases activity of PFKI.

#D. True. Depending on the type of allosteric modulators. See #C.

#E. False. Allosteric enzymes have one or more regulatory sites distinctly different from the substrate-catalysis (binding or active site) site. Binding of the modulator at allosteric site affects binding of substrate to the active site of enzyme. Therefore, the activity of same enzyme is regulated by allosteric modulators without requiring another regulatory enzyme.

#F. True. Many proteins/enzymes involved in cell-cycle are selectively phosphorylated or dephosphorylated by CDK (cyclin dependent kinases) in order to regulate the specific events in cell cycle. In this process, the target enzyme is itself phosphorylated/ dephosphorylated (covalently modified) so regulate the event catalyzed by the target enzyme.       

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.