Question

___________ are always changed by participating in a reaction. (Choose all that are correct.) a. Enzymes b. Cofactors c. Reactants d. Coenzymes

Short answer

The correct answer is (c) Reactants.

Step-by-step solution

Understand the Components

In a chemical reaction, several components are involved. It is important to identify which components typically undergo change during a reaction. Reactants are always changed, while enzymes, cofactors, and coenzymes might not be modified.

Define Reactants

Reactants are substances that start a chemical reaction. In every reaction, reactants are consumed and transformed into products. Thus, they are always changed during the reaction.

Analyze Enzymes

Enzymes are proteins that act as catalysts to speed up chemical reactions. They are not consumed or permanently altered during the reaction, allowing them to act repeatedly.

Consider Cofactors

Cofactors are non-protein substances that assist enzymes during the catalysis of reactions. While they can be transiently associated with the enzyme or reactants, they are often regenerated in their original form.

Examine Coenzymes

Coenzymes are organic molecules that bind to enzymes and assist in catalysis. Unlike enzymes, they may undergo temporary changes during the reaction, but by the end of the catalytic cycle, they are usually regenerated.

Identify the Correct Options

Based on the analysis, the substance that is always changed by a chemical reaction is the reactant. Thus, the correct answer is (c) Reactants.

Key concepts

Reactants

In the realm of chemical reactions, reactants are the starting substances that undergo transformation during the reaction process. Imagine a recipe where ingredients are mixed to create a dish—in chemical reactions, reactants are these ingredients. When a reaction occurs, these reactants are consumed and changed into different substances known as products.

This transformation is fundamental. For instance, in the reaction between hydrogen and oxygen to form water, both hydrogen and oxygen are reactants. As the reaction proceeds, they transform into water, the product. It's essential to note that reactants are always changed in a chemical reaction, distinguishing them from other participants like enzymes or cofactors, which often remain unchanged.

Enzymes

Enzymes are remarkable proteins that serve as catalysts, making them crucial in speeding up chemical reactions without being consumed. Think of enzymes as your kitchen helpers that continually work to prepare meals without altering themselves. This catalytic nature is pivotal across many biological processes, as it allows reactions to occur at a much faster rate than they would in the enzyme's absence.

These proteins provide an alternative reaction pathway with a lower activation energy, essentially offering a shortcut that accelerates the reaction. While enzymes are not changed permanently by the reaction, they create an environment in which reactants can convert into products more efficiently. Nevertheless, once the reaction is complete, enzymes return to their original state, ready to catalyze another cycle. Thus, enzymes play a supportive, yet pivotal role in reactions without being permanently altered.

Cofactors

Cofactors are non-protein components that assist enzymes in their role as catalysts. Imagine cofactors as small assistants that make sure enzymes function correctly. Without these helpers, the enzyme might not work as effectively or may not work at all.

Cofactors can be metal ions like zinc or magnesium; they might bind to an enzyme to ensure its structure is perfect for catalysis. They can also help enzymes interact with reactants more effectively. Typically, cofactors are not changed permanently during a reaction. Instead, they help facilitate the process and are regenerated in their initial form after the reaction proceeds. In this way, cofactors play a critical but temporary role in ensuring that reactions happen smoothly.

Coenzymes

Coenzymes bear a similarity to cofactors but are distinct in their composition and function. They are organic molecules that bind to enzymes and play an essential role in the catalysis of reactions. Coenzymes can be compared to specialized tools that provide enzymes with atomic or group transfers necessary for the reaction.

For example, vitamins often act as coenzymes. They attach to enzymes, undergo small changes to help the enzyme act on a substrate, and then leave the enzyme once the reaction is complete, usually in their original form. However, during the reaction, coenzymes may become altered temporarily, but by the end of the catalytic cycle, they are generally regenerated, allowing them to assist in further reactions. Coenzymes are crucial for the proficiency of many types of enzymatic reactions, acting as vital facilitators in the complex orchestra of life’s chemistry.