Advanced Placement (AP) Biology Practice Exam

What is the primary function of enzymes in metabolic pathways?

1. To release energy continuously

2. To catalyze reactions selectively at the active site

3. To absorb energy from the surroundings

4. To increase the activation energy needed

The correct answer is: To catalyze reactions selectively at the active site

The primary function of enzymes in metabolic pathways is to catalyze reactions selectively at the active site. Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for those reactions to occur. This specificity is critical because it allows enzymes to facilitate only particular reactions, thereby helping to regulate and coordinate numerous metabolic pathways within the cell. Each enzyme has a unique active site that is tailored to fit a specific substrate, much like a lock and key, ensuring that only the intended reactions are accelerated. By providing an optimal environment for the reaction to take place, enzymes not only increase the rate of reaction but also enable the cell to perform complex functions in a controlled manner while maintaining homeostasis. This selective catalysis is key to cellular metabolism and overall organismal health.