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:
Damage from hypoxia is often seen in the hippocampus, the area of the brain that creates memories. Some toxic chemicals can attach onto the body's oxygen and cause brain damage from lack of oxygen, depending on the duration of the exposure and the level of chemical one is exposed to.