Kaplan Nursing Entrance Practice Exam

What is true about enzymes in human cells?

1. They are carbohydrates

2. They are proteins that work best at pH 7.2

3. They are nucleic acids

4. They are lipids that catalyze reactions

The correct answer is: They are proteins that work best at pH 7.2

Enzymes in human cells are indeed proteins, which are essential for catalyzing biochemical reactions. They facilitate these reactions by lowering the activation energy required, thereby speeding up the processes necessary for life. While enzymes can function within a range of pH levels depending on their specific role and the environment, many enzymes in human cells do operate optimally around a neutral pH, approximately 7.2. This pH level aligns with the conditions found in most human tissues, where enzyme activity is crucial for metabolic processes. The other options incorrectly identify enzymes. Enzymes are not carbohydrates or nucleic acids; rather, they are primarily composed of amino acids, which form proteins. While lipids play important roles in cellular structures and energy storage, they do not function as catalysts in the same way enzymes do. Understanding the structural nature of enzymes as proteins is vital in appreciating their function and the importance of pH in their activity.