Question

When most biological enzymes are heated, they lose their catalytic activity. This process is called denaturing. The change original enzyme \(\rightarrow\) new form that occurs on heating is endothermic and spontaneous. Is the structure of the original enzyme or its new form more ordered (has the smaller positional probability)? Explain.

Short answer

The structure of the original enzyme is more ordered (has a smaller positional probability) than its new form after the endothermic and spontaneous denaturing process. This is because the entropy of the system increases, implying a decrease in order, as the process proceeds.

Step-by-step solution

Understand the given information

We are given that the denaturing process of a biological enzyme is heating is endothermic and spontaneous. Endothermic means that the reaction absorbs heat from its surroundings, and spontaneous means that the reaction occurs naturally without any external input.

Define entropy and relate it to the spontaneity of a reaction

Entropy is a measure of the degree of disorder or randomness in a system. It is often represented by the symbol \(S\). In general, the entropy of a system increases with increasing disorder. A spontaneous reaction is characterized by an increase in entropy, which means that the system becomes more disordered after the reaction.

Consider entropy changes during denaturing process

During the denaturing process, the enzyme loses its catalytic activity, which means that its structure changes. Since the process is endothermic and spontaneous, it suggests that the entropy of the system has increased.

Determine the structure with a smaller positional probability

A smaller positional probability implies a higher degree of order in the system. Since the system's entropy has increased during the denaturing process, it means that the degree of order has decreased. Therefore, the original structure of the enzyme must have a smaller positional probability, indicating that it is more ordered compared to the new form after heating.

Conclusion

The structure of the original enzyme is more ordered (has a smaller positional probability) than its new form after the endothermic and spontaneous denaturing process. This conclusion is based on the relationship between entropy, spontaneity, and positional probability.

Key concepts

Entropy

Entropy is an essential concept in thermodynamics that measures the level of disorder or randomness in a system. Essentially, it reflects how energy is distributed in a system. When a reaction or change occurs, we often look at whether the entropy increases or decreases.

• A high entropy value indicates a disordered state; particles are spread out randomly.
• On the other hand, low entropy means a structured, ordered state where particles are less randomized.

In the context of enzyme denaturation, when the enzyme loses its catalytic structure, it signifies an increase in disorder. Therefore, the entropy increases because the enzyme's structured and ordered form unfolds into a less ordered and more random shape. This disordering of structure directly shows how entropy grows as the enzyme denatures.
Such an understanding helps us grasp why the original state of a biological molecule, like an enzyme, is typically more ordered than when it's denatured, which is a more chaotic state.

Spontaneous Reaction

A spontaneous reaction is a process that occurs without needing external energy input. This intrinsic ability to proceed refers directly to thermodynamic principles.

• In the case of enzyme denaturation, the reaction is labeled as spontaneous because it naturally occurs upon heating, driven by internal factors like changes in entropy.
• Generally, for a reaction to be spontaneous, the total entropy change of the system and surroundings is positive or favorable.

In the heating and unfolding of enzymes, the increase in the system's entropy due to unfolding means the process can proceed without extra energy input. Hence, it is spontaneous. Even though the reaction is endothermic, the entropy increase implies that the system becomes more disordered, enabling this natural progression to occur. Understanding spontaneous reactions in this context helps explain why enzymes lose function so easily with heat.

Endothermic Process

An endothermic process is one in which a system absorbs heat from its surroundings. Unlike exothermic processes that release heat, endothermic reactions require heat input to happen.

• The denaturation of enzymes is an endothermic process because it requires heat to unfold the protein structure.
• This heat absorption is vital to overcoming the stability of the enzyme's folded, functional form.

In biological terms, bringing the enzyme's tightly coiled structure into a more relaxed and random state needs external energy. Since this transformation absorbs heat, contributing to the system’s disorder as described by entropy, it fits into the broader picture of why these reactions are both endothermic and spontaneous.

Positional Probability

Positional probability is a concept that refers to the likelihood of a system or molecule being in a particular arrangement or position. In a more ordered system, particles or molecules are often in a specific, fixed arrangement.

• For an enzyme, the folded, active form has lower positional probability because its structure is quite specific and highly ordered.
• After heating and denaturing, the enzyme shifts to a form with a higher positional probability due to increased energy and disorder.

Understanding positional probability helps explain why the original structure of an enzyme, before denaturation, is more ordered and less probable than its denatured form. Essentially, as the enzyme moves from its structured to its less structured form, the positional probability increases with the heightened randomness and entropy, aligning perfectly with thermodynamic principles.