The diagrams below represent the shapes of an enzyme molecule and its substrate - Scottish Highers Human Biology - Question 4 - 2016

To solve this question, we need to identify the shapes of inhibitors that can interact with the enzyme molecule.

1. Understanding Competitive Inhibitors:

   • Competitive inhibitors resemble the substrate and can bind to the active site of the enzyme, preventing the substrate from binding. Thus, a competitive inhibitor should have an overall shape that closely matches the substrate.

2. Understanding Non-Competitive Inhibitors:

   • Non-competitive inhibitors do not necessarily resemble the substrate and bind to a different site, which alters the enzyme's function regardless of substrate presence. Their shape can differ from both the substrate and the enzyme itself.

3. Analyzing the Given Options:

   • A: Circle and Triangle – The circle does not resemble the substrate shape closely enough.
   • B: Square and Rectangle – The square could match the enzyme's active site, making it a potential competitive inhibitor, while the rectangle does not resemble the substrate closely.
   • C: Rectangle and Circle – The rectangle could potentially act as a competitive inhibitor, but the circle does not match the substrate.
   • D: Triangle and Triangle – Both shapes do not closely resemble the active site or the substrate.

After evaluating the options, Row B showcases a possible competitive (Square) and non-competitive (Rectangle) inhibitors, as the square matches the shape of the enzyme's active site better than the others.