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:
Types of Hypoxia. As noted above, there are different types of hypoxia, or reasons that there is not enough oxygen in the tissues of the body. Hypoxic hypoxia (hypoxemic hypoxia) â- In this type of hypoxia, the tissues do not have enough oxygen because there is a lack of oxygen in the blood flowing to the tissues.