NANP Board Practice Exam

Where is most creatine transported to and phosphorylated into phosphocreatine?

1. Heart muscle cells

2. Liver cells

3. Skeletal muscle cells

4. Stomach cells

The correct answer is: Skeletal muscle cells

Creatine plays a crucial role in energy production, particularly in high-intensity exercise or activities that require short bursts of energy. The majority of creatine in the body is transported to the skeletal muscle cells. Inside these cells, creatine is then phosphorylated to form phosphocreatine. This process is vital because phosphocreatine serves as a rapidly mobilizable reserve of high-energy phosphates, which can regenerate adenosine triphosphate (ATP), the primary energy carrier in cells. Skeletal muscle cells are particularly suited for this function due to their role in facilitating quick and explosive movements, making them the primary storage site for phosphocreatine. While other tissues, such as the heart and liver, may handle some creatine, their roles do not primarily center around the same rapid energy demands required during muscular contractions, especially in explosive activities like sprinting or heavy lifting. Therefore, the emphasis on skeletal muscle cells clarifies why this is the correct answer.