Q: A reaction has $$\Delta H = -100\ \mathrm{kJ}$$, $$\Delta S = +0.2\ \mathrm{kJ/K}$$, and occurs at $$T = 300\ \mathrm{K}. $$Calculate $$\Delta G$$ for this reaction.

$$\Delta G = -100\ \mathrm{kJ} - (300\ \mathrm{K} \times 0.2\ \mathrm{kJ/K}) = -100\ \mathrm{kJ} - 60\ \mathrm{kJ} = -160\ \mathrm{kJ}$$

Question 1

Which statement best describes the difference between anabolic and catabolic pathways in cellular metabolism?

Accepted Answer

Anabolic pathways build complex molecules from simpler ones, requiring energy input, while catabolic pathways break down complex molecules into simpler ones, releasing energy.

Question 2

According to the first law of thermodynamics, which of the following is true about energy in biological systems?

Accepted Answer

Energy can be transferred and transformed, but cannot be created or destroyed.

Question 3

A cell uses ATP hydrolysis to drive the endergonic synthesis of glutamine from glutamic acid and ammonia. If the hydrolysis of ATP releases $$\Delta G = -30.5\ \mathrm{kJ/mol}$$ and the synthesis of glutamine requires $$\Delta G = +14.2\ \mathrm{kJ/mol}$$, what is the overall $$\Delta G$$ for the coupled reaction?

Accepted Answer

$$\Delta G = -16.3\ \mathrm{kJ/mol}$$

Question 4

Which of the following best explains why enzymes are necessary for many biological reactions?

Accepted Answer

Enzymes lower the activation energy ($$E_a) $$required for a reaction to proceed.

Question 5

Which of the following is a correct application of the second law of thermodynamics to living organisms?

Accepted Answer

Every energy transfer in living organisms increases the entropy of their surroundings.

Question 6

A reaction has $$\Delta H = -100\ \mathrm{kJ}$$, $$\Delta S = +0.2\ \mathrm{kJ/K}$$, and occurs at $$T = 300\ \mathrm{K}. $$Calculate $$\Delta G$$ for this reaction.

Accepted Answer

$$\Delta G = -100\ \mathrm{kJ} - (300\ \mathrm{K} 	imes 0.2\ \mathrm{kJ/K}) = -100\ \mathrm{kJ} - 60\ \mathrm{kJ} = -160\ \mathrm{kJ}$$

Question 7

Which of the following statements about ATP is correct?

Accepted Answer

Energy is released from ATP when the terminal phosphate bond is broken by hydrolysis.

Question 8

Which scenario best illustrates energy coupling in a cell?

Accepted Answer

A cell uses the energy released from glucose breakdown to pump ions against their concentration gradient.

Question 9

Which of the following would most likely increase the rate of an enzyme-catalyzed reaction that is currently limited by substrate concentration?

Accepted Answer

Increasing the amount of enzyme present.

Question 10

A competitive inhibitor affects an enzyme by:

Accepted Answer

Competing with the substrate for binding at the active site.

Question 11

Which of the following is true about noncompetitive inhibition?

Accepted Answer

The inhibitor binds to a site other than the active site, altering enzyme function.

Question 12

Which of the following best describes feedback inhibition in metabolic pathways?

Accepted Answer

The end product of a pathway binds to an enzyme, decreasing its activity and thus regulating the pathway.

Question 13

Which of the following is an example of an open system in biology?

Accepted Answer

A living cell exchanging materials and energy with its environment.

Question 14

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

Accepted Answer

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

Question 15

Which of the following statements about enzyme specificity is correct?

Accepted Answer

Enzyme specificity is determined by the shape of the active site and the substrate.

Question 16

A cell is exposed to a toxin that irreversibly binds to the active site of an essential enzyme. What is the most likely outcome?

Accepted Answer

The enzyme will be permanently inactivated, stopping the metabolic pathway.

Question 17

Which of the following best explains why most enzymes are proteins?

Accepted Answer

Proteins can form complex three-dimensional shapes necessary for substrate specificity.

Question 18

Which of the following is a correct statement about the relationship between free energy ($$\Delta G) $$and equilibrium?

Accepted Answer

A process is spontaneous and can perform work only when it is moving toward equilibrium ($$\Delta G \u003c 0).$$

Question 19

Which of the following is an example of allosteric regulation?

Accepted Answer

A regulatory molecule binds to a site other than the active site, changing enzyme activity.

Chapter 8: An Introduction to Metabolism – Study Notes

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