Which correctly describes the lock and key model?
- A. Enzyme undergoes a change in shape to accommodate the substrate at the active site. No. In a lock and key model, the substrate and the active site of the enzyme need to be identical in terms of shape, so this wouldn't happen.
- Next, the enzyme irreversibly binds to the substrate to form products. Now here it doesn't matter which of the two models we follow, this is not going to happen. It can't be irreversibly binding. Remember, it needs to be a non-covalent bond between the substrate and the active site of the enzyme. In that way, the substrate can attach, get transformed into products, and then be released from the enzyme.
- C. Active site of enzyme has a fixed shape that perfectly matches the shape of the substrate. This is true. This is the lock and key model.
- D. The enzyme is able to interact with many different substrates. Now, here in lock and key model, the active site and the substrate need to be perfect. They need to be identical to one another. This greatly limits the types of substrates and the variety of substrates that can attach, so this would not be true. You wouldn't be able to get many different substrates attaching. You need a more flexible shape in terms of the active site, which is not the lock and key model.
So here, option C would be our only answer.