Lock and Key Model. Each type of enzyme has a unique 3-D shape, including a surface groove called an active site, which fits its target substrate much like a key fits in a lock. Other substances that donât fit can't enter the active site and no reaction occurs.
Some of the many causes of hypoxia are the following: 1  Chemical or gas poisoning (for example cyanide, carbon monoxide) 2  Low or absent concentration of oxygen (for example, high altitudes reached without supplemental oxygen as seen in mountain climbing, and aviation, drowning or fires)  Lung problems, for example:
There are four types of HYPOXIA : 1. Hypoxic hypoxia is the most common and is caused by decreased oxygen in air or the inability to diffuse the oxygen across the lungs. If this happens, the person has less than 100% saturation of the blood in the arteries.. Hypoxic hypoxia is the most common and is caused by decreased oxygen in air or the inability to diffuse the oxygen across the lungs. If this happens, the person has less than 100% saturation of the blood in the arteries.