Cellular reproduction requires a nucleus and a mitochondria in order to perform mitosis, the process of cell division. Mature red blood cells do not contain a nucleus or mitochondria, making mitosis impossible.
Immature red blood cells contain a nucleus and mitochondria in order to acquire the necessary hemoglobin protein to develop into a mature red blood cell. Once an immature red blood cell produces the cell's maximum capacity of hemoglobin protein, the nucleus and mitochondria are broken down into different molecules for other processes. Red blood cell production rapidly takes place in bone marrow, producing approximately 7 trillion new cells each month.