How Do Cells Control the Rate of Cellular Respiration?

How Cellular Respiration Works

• Cell respiration is a complex process, with three different cycles. Glycolysis is responsible for breaking down glucose, and the electron transport chain takes electrons from the decomposition of glucose and uses them to generate adenosine tri-phosphate (ATP), which the cells use for energy. The Krebs cycle teams with glycolysis in glucose breakdown, but also stores the energy from that in ATP. In the absence of oxygen, cells may resort to anaerobic respiration, which is much less efficient but still provides fuel to the cell so it can function properly. Anaerobic respiration may begin when the body is working so hard that it cannot provide enough oxygen to produce the necessary energy--for example, during a race or a very intense workout.
  
  

Controlling Cellular Respiration

• The rate of cell respiration is determined by supply and demand, just like gas prices. If the body is working hard, cell respiration speeds up, and when demand is not so high (during sleep, for example), respiration is slowed. Within the cell, there is an intricate network of enzymes that serve as signals to the cell to speed up or slow down. The most significant enzyme is phosphofructokinase, which spurs an early step in the respiration cycle. If ATP accumulates in the cell, phosphofructokinase is inhibited, slowing the process of respiration. As ATP is consumed, phosphofructokinase becomes active again and the respiration rate increases. This enzyme is also inhibited by an excess of citrate, which is produced during the Krebs cycle, and therefore helps ensure that glycolysis and the Krebs cycle operate in sync.
  
  

Efficiency of Cell Respiration

• The sensitivity of the enzymes controlling cell respiration allows cells to be extremely economical in their production of energy. Cells regulate not only the overall rate of respiration, but also the production of individual amino acids during various steps of the respiration cycle. If carbohydrates are not available, the cell has multiple pathways for breaking down proteins or fats to use in the Krebs cycle. Cell respiration converts about 40 percent of the fuel consumed into usable energy, and the rest is lost as heat.