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:
Some individuals can experience oxygen levels which are decreased because of deformities or hemoglobin deficiency. This condition is also known as carbon monoxide poisoning as well as hypemic hypoxia. Smoking is also a common cause of hypoxia as it is a common cause of many problems with the body. No matter what illness you read about, you will almost always find smoking as a contributing cause.