Biochemistry : Thermodynamic Regulation

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #1 : Thermodynamic Regulation

Which of the following statements are incorrect?

Possible Answers:

A spontaneous reaction always happens quickly

A spontaneous reaction can still occur with a large decrease in entropy

A negative enthalpy is favorable for a spontaneous reaction

A spontaneous reaction proceeds in the forward direction with a negative Gibbs free energy value

A nonspontaneous reaction will proceed spontaneously when reversed

Correct answer:

A spontaneous reaction always happens quickly

Explanation:

 

The spontaneity of a reaction says nothing about the reaction's speed. For a spontaneous reaction, the change in Gibbs free energy is negative. In other words, the products have lower energy than the reactants. With low temperatures and negative enthalpy, a reaction can still proceed spontaneously if entropy decreases. 

Example Question #41 : Homeostasis And The Biological Environment

A reaction has a change in Gibbs free energy () of . This reaction is __________.

Possible Answers:

Not enough information given.

endergonic and spontaneous

endergonic and non-spontaneous

exergonic and spontaneous

exergonic and non-spontaneous

Correct answer:

exergonic and spontaneous

Explanation:

The Gibbs Free Energy ()of a reaction tells us whether or not the reaction is favorable. A favorable reaction is also known as spontaneous, and has a negative . A non-favorable reaction is non-spontaneous, and has a positive . The term exergonic (meaning energy exits the system) is also used for a reaction with a negative , while the term endergonic (meaning energy enters the system) is used for a reaction with a positive . Therefore, a reaction with  is both exergonic and spontaneous. 

Example Question #42 : Homeostasis And The Biological Environment

What can be said about the rate of a reaction with a  less than zero compared to the rate of a reaction with a  greater than zero?

Possible Answers:

Nothing can be said about reaction rate from the information given.

The rate is faster.

The rate of the reaction is only faster when the temperature is low.

The rate is slower.

The rates are equal.

Correct answer:

Nothing can be said about reaction rate from the information given.

Explanation:

Gibbs Free Energy () is a thermodynamic principle that tells us about only about the spontaneity of a reaction (whether or not the reaction will occur). On the other hand, the rate of a reaction can be described by chemical kinetics. The question gives no information about the kinetics of the reaction, and we therefore cannot draw any conclusions about the rates of the two reactions described.

Example Question #43 : Homeostasis And The Biological Environment

In humans, heat is generated by uncoupling oxidative phosphorylation from ATP production during which process?

Possible Answers:

ATP-hydrolyzing substrate cycles

ATP hydrolysis during muscle contraction

Vasodilation of blood vessels

Metabolism in brown fat cells 

Sweating

Correct answer:

Metabolism in brown fat cells 

Explanation:

The correct answer is "metabolism in brown fat cells." The mitochondria in brown fat have a protein called thermogenin that acts as a proton channel, which allows the dissipation of the proton gradient made by the electron transport chain. This allows oxidative phosphorylation to continue, and produce heat, without the production of ATP. Answers a and b, which both involve ATP hydrolysis, are also used by humans to produce heat but do not involve the uncoupling of oxidative phosphorylation from ATP production. Sweating and vasodilation of blood vessels are both ways that the human body loses heat.

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