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:
circulatory hypoxia stagnant hypoxia. histotoxic hypoxia that due to impaired utilization of oxygen by tissues, as in cyanide poisoning. hypoxemic hypoxia (hypoxic hypoxia) that due to insufficient oxygen reaching the blood, as at the decreased barometric pressures of high altitudes.stagnant hypoxia that due to failure to transport sufficient oxygen because of inadequate blood flow, as in heart failure.ffinity hypoxia hypoxia resulting from failure of the hemoglobin to release oxygen to the tissues, as may occur with a left-shifted oxyhemoglobin dissociation curve.