Which of the following is INCORRECT for the lock-and-key model?

The binding of the substrate produces a conformational change in enzyme

The correct answer is option 2. The binding of the substrate produces a conformational change in enzyme.

The lock-and-key model is a conceptual model used to describe the specificity of enzyme-substrate interactions. Here's a detailed explanation of each statement and why the incorrect one is inaccurate:

1. It demonstrates enzyme-substrate complex:

The lock-and-key model indeed demonstrates the formation of an enzyme-substrate complex. In this model, the enzyme's active site is depicted as a rigid structure that perfectly matches the shape of the substrate, much like a lock (enzyme) and key (substrate) fitting together. So, the statement is correct.

2. The binding of the substrate produces a conformational change in the enzyme:

This statement is incorrect in the context of the lock-and-key model. According to this model, the enzyme's active site is preformed and complementary to the substrate's shape without requiring a conformational change. The substrate binds to the enzyme's active site like a key fitting into a lock, without inducing significant structural alterations in the enzyme.

In the lock-and-key model, the enzyme's active site is depicted as rigid and specific to the substrate. The model does not account for conformational changes in the enzyme upon substrate binding. However, this aspect is addressed by the induced fit model, where the binding of the substrate induces conformational changes in the enzyme to achieve a tighter fit.

3. The active site of the enzyme is complementary to the substrate:

This statement is a fundamental aspect of the lock-and-key model. It describes how the shape and chemical properties of the enzyme's active site precisely match those of the substrate, allowing for selective binding and catalysis. So, the statement is correct.

4. It is used to describe the binding process:

The lock-and-key model is indeed used to describe the binding process between enzymes and substrates. It provides a visual analogy of how enzymes interact with substrates based on their complementary shapes, much like a lock and key. So, the statement is correct.

In summary, the lock-and-key model accurately describes the enzyme-substrate complex formation and emphasizes the specificity of enzyme-substrate interactions. However, it does not account for conformational changes in the enzyme upon substrate binding, which is a feature addressed by the induced fit model.