Q: A chemical reaction has a change in enthalpy $$\Delta H = -100 kJ/$$mol, a change in entropy $$\Delta S = 0.2 kJ/($$mol\cdot K), and occurs at $$T = 300 K. $$What is the change in free energy $$\Delta G$$ for this reaction?

$$\Delta G = -100 - (300 \times 0.2) = -100 - 60 = -160 kJ/$$mol

Question 1

Which of the following best describes the difference between catabolic and anabolic pathways in metabolism?

Accepted Answer

Catabolic pathways release energy by breaking down complex molecules, while anabolic pathways consume energy to build complex molecules.

Question 2

A chemical reaction has a change in enthalpy $$\Delta H = -100 kJ/$$mol, a change in entropy $$\Delta S = 0.2 kJ/($$mol\cdot K), and occurs at $$T = 300 K. $$What is the change in free energy $$\Delta G$$ for this reaction?

Accepted Answer

$$\Delta G = -100 - (300 	imes 0.2) = -100 - 60 = -160 kJ/$$mol

Question 3

Which of the following statements about the first and second laws of thermodynamics is correct in the context of biological systems?

Accepted Answer

The first law states that energy can be transferred or transformed but not created or destroyed, and the second law states that every energy transfer increases the entropy of the universe.

Question 4

Which of the following best explains why ATP hydrolysis is used to drive endergonic reactions in cells?

Accepted Answer

ATP hydrolysis releases free energy, which can be coupled to endergonic reactions to make the overall process exergonic.

Question 5

A scientist is studying an enzyme-catalyzed reaction. She increases the temperature from 25°C to 60°C and observes that the reaction rate first increases, then sharply decreases. What is the most likely explanation for the decrease in reaction rate at higher temperature?

Accepted Answer

The enzyme is denatured at high temperatures, losing its functional shape.

Question 6

Which of the following is true regarding the effect of enzymes on chemical reactions?

Accepted Answer

Enzymes lower the activation energy ($$E_a) $$but do not change the $$\Delta G of $$the reaction.

Question 7

A metabolic pathway in a cell is regulated by feedback inhibition. Which of the following best describes this process?

Accepted Answer

The end product of the pathway binds to an enzyme early in the pathway, inhibiting its activity and thus slowing down the pathway.

Question 8

Which of the following is an example of a competitive inhibitor?

Accepted Answer

A molecule that binds to the active site of an enzyme, preventing the substrate from binding.

Question 9

A reaction has $$\Delta G = +30 kJ/$$mol. Which of the following statements is true about this reaction?

Accepted Answer

The reaction is endergonic and requires an input of energy to proceed.

Question 10

Which of the following best describes the role of allosteric regulation in enzyme activity?

Accepted Answer

A regulatory molecule binds to a site other than the active site, causing a conformational change that affects enzyme activity.

Question 11

Which of the following is a real-life example of energy transformation that illustrates both the first and second laws of thermodynamics?

Accepted Answer

A plant using sunlight to make organic molecules, releasing heat in the process.

Question 12

Which of the following statements about metabolic equilibrium in living cells is correct?

Accepted Answer

Cells never reach metabolic equilibrium because they are open systems with a constant flow of materials.

Question 13

A patient is diagnosed with a deficiency in a vitamin that acts as a coenzyme. Which of the following is the most likely effect on the patient's metabolism?

Accepted Answer

The patient will have decreased rates of enzyme-catalyzed reactions that require that coenzyme.

Question 14

Which of the following best explains why increasing substrate concentration can overcome the effects of a competitive inhibitor but not a noncompetitive inhibitor?

Accepted Answer

Competitive inhibitors bind to the active site, so more substrate can outcompete the inhibitor, while noncompetitive inhibitors bind elsewhere and change the enzyme's shape.

Question 15

Which of the following is NOT a way that enzymes lower the activation energy ($$E_a) of a $$reaction?

Accepted Answer

Increasing the free energy ($$\Delta G) of $$the reaction.

Question 16

A cell is observed to have a high concentration of ADP and a low concentration of ATP. Which of the following is most likely occurring in the cell?

Accepted Answer

The cell is actively synthesizing ATP from ADP using energy from catabolic reactions.

Question 17

Which of the following best describes the concept of energy coupling in cellular metabolism?

Accepted Answer

Using the energy released from an exergonic reaction to drive an endergonic reaction.

Question 18

A mutation causes an enzyme to lose its ability to bind its substrate. Which of the following is the most likely explanation?

Accepted Answer

The mutation altered the shape of the enzyme's active site, preventing substrate binding.

Question 19

Which of the following is an example of an exergonic reaction in a living cell?

Accepted Answer

The hydrolysis of ATP to ADP and inorganic phosphate.

Chapter 8: An Introduction to Metabolism – Study Notes

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