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:
Occurs if the cell is unable to maintain homeostasis. Most common cause -hypoxia-lack of sufficient O2. Results from reduced amount of O2 in air, loss of hemoglobin or decreased efficacy of hemoglobin, decreased production of RBC, poisoning of the oxidative enzymes within cells.