National League for Nursing (NLN) Science Practice Exam

The process by which an enzyme acts on its substrate is best described by which model?

1. Lock-and-key model

2. Enzyme-and-substrate model

3. Enzyme folding model

4. Catalytic model

The correct answer is: Lock-and-key model

The lock-and-key model is a widely accepted representation of how enzymes interact with their substrates. This model illustrates that enzymes have a specific active site, precisely shaped to fit a particular substrate, much like a key fits into a lock. When the correct substrate enters the active site of the enzyme, it forms an enzyme-substrate complex, enabling the reaction to proceed. The specificity implied by the lock-and-key model emphasizes that each enzyme is tailored to work with a specific substrate, underscoring the unique biochemical pathways that enzymes facilitate. This model effectively explains the high fidelity of enzyme-substrate interactions and the role enzymes play in catalyzing biochemical reactions. Other options may reference concepts related to enzyme function but do not convey the specificity and interaction dynamics illustrated by the lock-and-key model. For instance, the enzyme-and-substrate model, while it captures the essence of enzyme-substrate interactions, lacks the specificity detail that the lock-and-key model provides. The enzyme folding model focuses on the three-dimensional structure of the enzyme but is less about interaction. The catalytic model may emphasize the overall mechanism of action but does not encapsulate the fitting nature of how substrates interact with enzymes as effectively as the lock-and-key model does.