Do Red Blood Cells have Nucleus and Mitochondria? And if not present, then why? Let’s Know!

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The nucleus is also known as the brain of the cell, and it is a membrane-bound organelle found in the eukaryotic cells only. It contains all the genetic material required to run the cell and its various molecular pathways. It is also the place where the proteins are produced.

In the other case, mitochondria are the powerhouse of the cell that produces the required cellular ATP energy needed to run the cell and carry out cellular respiration. It is the organelle inside the cell where Pyruvate oxidation, the Krebs cycle, and Oxidative Phosphorylation occur based on the cell type.

It is to be noted that Red Blood Cells are those types of cells that don’t have any nucleus and so they totally lack genetic materials. Also that, Red Blood Cells lack mitochondria as well and so they also lack mtDNA and are able to respire anaerobically to produce energy.

Red Blood Cells have adapted to various characteristics with the absence of nucleus and mitochondria for several reasons which also gives them their distinctive biconcave appearance.

We’ll learn more about these and will get most of your queries cleared. So, let’s get started…

Do Red Blood Cells have Nucleus?

Mammalian red blood cells do not have a nucleus, however, red blood cells of Chondrichthyes (cartilaginous fishes), Osteichthyes (bony fishes), Amphibians, Reptiles, and Birds do have a nucleus but its totally inactive.

However, there are some exceptions, like the Salamanders of the genus Batrachoseps, and fishes that fall under the genus Maurolicus do not contain a nucleus in their RBC.

It is to be noted here that the immature mammalian red blood cells do have the nucleus and the genomic contents in them.

But, as these immature cells grow and divide into daughter cells and start to synthesis their own hemoglobin, they also start to destroy their nucleus along with the genetic contents inside it.

So, when the red blood cells become fully mature with having the full presence of hemoglobin molecule inside it then they would have already destroyed their whole nuclear material.

This process of immature red blood cells destroying their own nucleus occurs in the liver cell of mammalian embryos, and in the bone marrow cells of adult mammals.

So, it is here in the liver of the embryo and the bone marrow of the adults where the immature RBCs get mature fully before being released into the bloodstream.

And so, here in the process they lose their nucleus and become mature by taking the enucleated disc-shaped flattened-concave center, which is also known as the biconcave shape of mature RBCs.

Only immature RBCs have the capability of cell division, while the mature RBCs cannot divide or replicate and make proteins at all. This is also due to their loss of DNA along with the nucleus, as the DNA only has the power to replicate leading to cell division and also to form proteins.

As the mature RBCs cannot divide and replicate because of having little to no cell repair capabilities due to the absence of a protein-producing system, so, it is also impossible for any kind of virus to target the mammalian red blood cells and replicate the viral copies in order to cause any kind of viral infection. Note this!


Do Red Blood Cells have Mitochondria?

Mammalian red blood cells do not have mitochondria, however, the red blood cells of lower vertebrates like fish, amphibians, reptiles, and aves (birds) do have functional mitochondria in them.

When the immature red blood cells develop and divide to produce mature number of daughter red blood cells then they do loss their mitochondria in the process as well along with the nucleus and other cell organelles like Golgi apparatus and Endoplasmic Reticulum.

All of these losings of mitochondria happens in the liver cells of embryos and in the bone marrow of adults. Only the amitochondriated RBCs enters into the bloodstream to match other mature RBCs.

So, the mature RBCs due to the absence of mitochondria and also the nucleus only possess a size of about 7.5 to 8.7 μm in diameter and 1.7 to 2.2 μm in thickness.

In the RBCs of lower vertebrates, the mitochondria remain relatively very less functional and so exhibit low content of respiratory enzymes and low respiratory activities in comparison to mammalian mitochondria.

And, as the RBCs do not actually need mitochondria they are able to survive for a very short timeperiod (approximately 120 days of lifespan) and respire without the need for oxygen.

RBCs rely solely on the cellular respiration process of anaerobic glycolysis in the cytoplasm (rather than oxidative phosphorylation carried out by mitochondria) for their energy metabolism. This is because anaerobic glycolysis doesn’t need oxygen while oxidative phosphorylation needs oxygen to carry out the cell respiration process.


Why Red Blood Cells do not have Nucleus?

Reasons why Red Blood Cells do not have Nucleus:

1. This is a type of natural adaptation of the red blood cells to accommodate a greater amount of hemoglobin in the cells. As hemoglobin protein is very important for carrying oxygen molecules by the cell, so allowing more free space within the compact body of the RBC by removing the nucleus is too beneficial to the cell.

2. It does not allow the cell to cause cell division as without nucleus and DNA contents RBC cannot conduct DNA replication, transcription, and translation, and so it is also not being able to synthesize new proteins.

3. Most of the major functions of the red blood cells are displayed in the cytoplasm where the hemoglobin is present. Not nuclear contents but hemoglobin is the major molecule here that occupies 95% of the dry weight of the red blood cell. If the hemoglobin level is lower than normal, it means you have a low red blood cell count and the absence of nuclear doesn’t allow this to happen.

4. As the immature red blood cells start to get mature, a ring of actin filaments forms around the cell that gradually contracts, gets inside the cell, and pinches off a segment of the cell that contains the nucleus, and so as a result the macrophages destroy the nucleus totally. The tension that was caused by the actin filaments while pinching and removing the nuclear contents also created tension in the cell membrane, and then that tension maintains the biconcave shape of the RBC. This shows that the lack of a nucleus is also the reason for the biconcave shape of RBC.

5. Another reason is that the mammalian RBC have a short life span of about 120 days because they are anucleated cells i.e. cells do not have a nucleus. It’s because there is no nuclear DNA inside to transcribe new RNA, and so, whatever RNA is left behind when the cell had DNA during its immature phase will only help in its future protein enzyme synthesis. And within 120 days or so, whatever enzymes are there will slowly decay leading to the death of the RBC in the spleen.


Why do Red Blood Cells do not have Mitochondria?

Reasons why Red Blood Cells do not have Mitochondria:

1. Presence of Mitochondria causes aerobic respiration. And that the red blood cells don’t actually need to respire aerobically i.e. they respire in the absence of oxygen. And, RBC’s role is to transport oxygen to all other cells of the body, and so if it had its own mitochondria then it would have used a great portion of the oxygen and would have wasted it rather than transporting it to the other parts of the body.

2. Anaerobic glycolysis happens within the cytoplasm of the cell in order to produce the required energy needed to conduct the oxygen transporting function of the RBC. This Anaerobic glycolysis occurs when glucose is broken down without the presence of oxygen.

3. In RBCs, which lack mitochondria and oxidative metabolism of cell respiration, pyruvate is reduced to lactic acid, a three-carbon hydroxyacid which is the product of anaerobic glycolysis.

4. The end product of anaerobic glycolysis is the synthesis of ATP and 2,3 DPG. ATP aids in oxygen delivery to the body tissues in a process to pump out the extra sodium and water from the red blood cells. This maintains the biconcave shape of RBCs and allows them to bend and flow smoothly through the body’s capillaries while facilitating the best of the oxygen transport process in the whole body. This shows that the lack of mitochondria is also the reason for the biconcave shape of RBC.

5. Also that, due to the removal of mitochondria and a few other cell organelles, the RBC gets enough room for the hemoglobin molecule to fit inside the compact cell and transport oxygen very easily. Because Mitochondria are absent and so oxygen is not utilized by the RBC to perform aerobic respiration so as a result, all oxygen gets transported to target body areas.

6. Also that, since RBC does not have a genome and so it may not support mitochondrial survival. It’s because only about 0.80% to 0.87% of proteins, which is around 13 proteins out of the 1300 different proteins present and used in mitochondria are actually produced by mtDNA and mitoribosomes, while the rest of the remaining 1287 proteins are produced by the nuclear DNA and nuclear ribosomes. And, as the nuclear DNA is absent the existence of mitochondria is also not possible in RBC.

7. It is also to be noted that the nuclear and mitochondrial removal out of the RBC may also help them to better adapt to high-sugar and high-heme conditions by limiting ROS generation. It’s because Reactive Oxygen Species (ROS) serve as cell signaling molecules, but sometimes high ROS generation can be damaging to the cell and its various other organelles, thus disrupting the normal cell physiology. So, this ROS generation needs to be limited and balanced in the RBC and the absence of mitochondria plays an important role in it.


What if Red Blood Cells had a nucleus?

If Red Blood Cells had a nucleus then it would have been very hard for the cells to enable more oxygen-carrying capacity in the blood and boosting our metabolism.

There would have been a little place for the hemoglobin to carry oxygen transportation, and so the carbon dioxide removal sophisticated transportation system may also get disrupted, resulting in your body not getting enough oxygen.

So, there would have been the need for more red blood cells to fulfill the rate of the body’s oxygen requirements, along with the balance in the whole body’s various processes which may need a greater evolutionary time period to complete. Or else, the various diseases and deficiencies can arise leading to the death of the individual.

On average, adult humans have somewhere around 25 trillion RBCs in their bodies. This constitutes 80% of our total body cells in number, and these rough constitute only around 4 percent of our total body mass.

This near-to-close estimation of the RBC helps in maintaining the proper oxygen flow in the body.

And, if the nucleus is present in the RBC then it may lead to the self-division capability to the RBC leading to a massive disruption in the homeostasis of the body.

Also that there would have been little to no tension by the actin filaments in the cell membrane, and so due to this, the biconcave shape of the RBC cannot be well-maintained. This shows that the lack of a nucleus is also the reason for the biconcave shape of RBC.


What if Red Blood Cells had mitochondria?

Just like the nucleus, if mitochondria remain present inside the RBC then this can also lead to a lack of space for the hemoglobin molecule. Thus, if fewer hemoglobin molecules remain present then this can negatively impact the oxygen-carrying capacity of the cell.

Each human red blood cell contains approximately 270 million of these hemoglobin molecules. So, the presence of mitochondria inside can lead to a decrease in the count of hemoglobin molecules inside the RBC.

If mitochondrial remains present inside the RBC, then this can lead to the use of oxygen by the RBC itself for performing aerobic respiration thus leading to the waste of oxygen and less oxygen transportation to the other cells of the body. This can lead to massive homeostatic disruption and oxygen deficiency leading to the death of the body.

As we all know that over the period of evolution, cells adapt themselves to be more actively metabolized. And so, if mitochondria are present in the RBCs, then chances are there that the cells will shortly choose to be modified in order to make the best use of Cytoplasm for energy generation by Anaerobic Glycolysis. This can make the mitochondria non-functional in nature. This will again make a lack of Space to carry Hemoglobin inside RBCs.

Also as the nucleus remains absent, so the 99% of proteins that the mitochondria will need to function will not be formed due to the lack of nuclear DNA. And so if the mitochondria adapt to synthesize all of these proteins all by itself then it may function or else it will remain non-functional at all with little to no self-dividing functionality.


CLARIFIED: Red Blood Cells totally lack nuclear DNA (nDNA), and mitochondrial DNA (mtDNA)

Yes, mature red blood cells totally lack nuclear DNA (nDNA) and mitochondrial DNA (mtDNA). The answer is straightforward, as the mature RBC lacks a nucleus, there is no chance for the presence of DNA in the cell.

In the same way, as the mature RBC lacks mitochondria there is also no chance for the presence of mDNA in the cell as well.

However, the immature RBC do have the nucleus and mitochondria and so they lack the nDNA and the mtDNA as well.

The DNA contents are required for these immature RBCs to replicate and divide just in order to reach the stage of becoming mature RBC. And, once these immature RBCs become mature they do lose all of their DNA and mitochondria and so lose the nDNA and mtDNA as well.

Yes, it’s true that mtDNA is not present in RBC. To prove this you can take RBC cells lysed in alkaline EDTA, bound to nitrocellulose, and hybridized to a radioactive mtDNA probe, and compare it to standards of known mtDNA concentration. You will find that no detectable mtDNA can be seen in RBC after the experiment.

And that, we also know that RBC cannot synthesize any RNA, nor cause cell division, nor have enough cell repair capabilities. So, this is all because of the absence of a nucleus and its nDNA inside it.

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