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:
A severe asthma attack, or flare, can cause hypoxia in adults and kids. During an attack, your airways narrow, making it hard to get air into your lungs. Coughing to clear your lungs uses even more oxygen and can make symptoms worse. Hypoxia can also result from lung damage due to trauma.