Question

1. Read the following:  
   • Erythrocytes (red blood cells) have no nuclei, mitochondria, or other organelles when they are mature. These organelles are ejected when the erythrocyte enters the bloodstream or shortly thereafter.
2. Post a paragraph that addresses the following:  
   • Should erythrocytes still be considered eukaryotic cells? Explain your rationale.
   • What do you predict would be the effects of having no nucleus? Explain.
   • In erythrocytes, the lack of mitochondria is an advantage. Why do you think this is true? Explain.

Answer 1

Red Blood Cells (RBCs) or erythrocytes are specialized cells present in our bloodstream for the transport of oxygen and carbon dioxide.  Mature erythrocytes  are biconcave disc-shaped cells, which lack nuclei and other organelles like mitochondria and golgi apparatus. The lack of organelles allows them to accommodate very large amounts of the protein haemoglobin, which is responsible for oxygen transport.

1. Mature RBCs develop in the bone marrow from haematopoetic stem cells. In the early stages of development, they contain all the organelles, which are responsible for the synthesis of all cellular proteins including haemoglobin. In the later stages of maturation, the organelles are removed by various processes such as autophagy, exosome- mediated removal , etc., to make more space for haemoglobin. Thus, even though mature erythrocytes lack organelles, they are still considered eukaryotic because they contain all eukaryotic organelles in their early stages of development.

2. Having no nucleus in the RBCs present several advantages:

a. It gives more space to accommodate larger amounts of haemoglobin.

b. It allows the cell to attain a biconcave shape which allows it to be more flexible.

c. Nucleus consumes a very large amount of energy. Hence, its removal also lessens the energy burden on the cell.

A disadvantage of not having a nucleus is that the cell cannot produce any new protein.

3. The lack of mitochondria is an advantage in erythrocytes for two reasons:

a.It provides space to accommodate more haemoglobin.

b. The lack of mitochondria ensures that the oxygen bound to the haemoglobin is not used up to produce energy in the cell. The energy requirements of the cell are met by the cytoplasmic process of glycolysis.