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Author Topic: Do red blood cells (erythrocytes) contain mitochondria?  (Read 38251 times)

Offline chris

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I was asked an interesting question on the radio the other day: "Red blood cells lack a nucleus, but do they also lack mitochondria?"


 

Offline RD

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Do red blood cells (erythrocytes) contain mitochondria?
« Reply #1 on: 02/12/2009 23:19:51 »
According to wikipedia ...

Quote
In mammals, erythrocytes also lose all other cellular organelles such as their mitochondria, golgi apparatus and endoplasmic reticulum. As a result of not containing mitochondria, these cells use none of the oxygen they transport; instead they produce the energy carrier ATP from glucose by a glycolysis pathway that ends with lactic acid production. Furthermore, red blood cells do not have an insulin receptor and thus their glucose uptake is not regulated by insulin. Because of the lack of nuclei and organelles, mature red blood cells do not contain DNA and cannot synthesize any RNA, and consequently cannot divide and have limited repair capabilities.
http://en.wikipedia.org/wiki/Red_blood_cell#Mammalian_erythrocytes
« Last Edit: 02/12/2009 23:23:36 by RD »
 

Offline chris

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Do red blood cells (erythrocytes) contain mitochondria?
« Reply #2 on: 03/12/2009 09:17:16 »
That's right; erythrocytes are the key oxygen carriers in the body and during their development they eject their nuclei (in mammals at least, but not birds and (scientists think) dinosaurs); they also lack mitochondria.

So how do they survive without mitochondria, which are the power-houses of most cells? Well, as has been pointed out above, red cells derive their energy via the process of glycolysis; glucose enters the cells freely, is phosphorylated - to glucose-6-phospate (6 carbons) - and then funnelled through the glycolysis pathway to make 2 molecules of pyruvate (3 carbons each), two molecules of reduced NAD (NADH) and some energy (ATP).

Normally the pyruvate is then converted to acetyl CoA, which is the 2 carbon substrate for the citric acid / Krebs Cycle, which takes place in the mitochondrial matrix space and the NADH donates the hydrogen (via the glycerol phosphate shuttle) to the electron transport chain to regenerate itself (to NAD).

However, as red cells lack mitochondria they have to find another way to regenerate their NAD and also to remove the pyruvate, which would other accumulate pathologically.

The solution is to use the enzyme lactate dehydrogenase to convert the pyruvate to lactic acid (the stuff that makes muscles feel tired after sustained exercise), driving the reaction with the NADH and regenerating the NAD in the process.

The lactate then exits the reb blood cell and travels via the bloodstream to the liver, which picks it up and turns it back into pyruvate which can then be converted back to glucose or burned to make more energy.

This is called the Cori cycle after the two scientists (called Cori!) who discovered it.

Chris
 

Offline glovesforfoxes

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Do red blood cells (erythrocytes) contain mitochondria?
« Reply #3 on: 04/12/2009 01:25:28 »
Are RBCs technically alive?

By the way chris - I believe the lactic acid hypothesis of muscle tiring has been disproved - I think the mechanism is now thought to be something to do with calcium ions & channels, but I can't remember exactly what that mechanism is. Perhaps you could search  some journals? I'm not entirely sure about this, but I remember questioning my biology teacher on it and she researched it for me.
« Last Edit: 04/12/2009 01:28:27 by glovesforfoxes »
 

Offline chris

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Do red blood cells (erythrocytes) contain mitochondria?
« Reply #4 on: 05/12/2009 22:41:24 »
It's not unreasonable to suggest that the pain of muscle fatigue could be provoked by lactate and potassium ions, I don't think. I'll check though.

Chris
 


Offline chris

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Do red blood cells (erythrocytes) contain mitochondria?
« Reply #6 on: 06/12/2009 09:32:32 »
Thanks for this; but these references refer to muscle fatigue, which is not what I meant. I was referring to the pain / burning sensation that develops in an acutely stressed muscle and which forces the movie bad guy to eventually let go of the rope from which he's been left dangling...

I think this acute discomfort is a combination of muscle mechanical stretch as well as the release of metabolites - potassium and lactate included - which trigger local nociceptors (pain sensors) to provoke the sensation of pain. For instance, when someone has a heart attack or angina they feel pain as the muscle begins to work anoxically. This cannot be down to calcium, otherwise people with chronic heart failure (as discussed in the NY times article) would be in pain perpetually.

It was specifically this pain to which I was referring.

However, thanks for these other references, which are really interesting in themselves.

Chris
 

Offline glovesforfoxes

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Do red blood cells (erythrocytes) contain mitochondria?
« Reply #7 on: 06/12/2009 13:10:54 »
Eh.. okay, but you did say:

Quote from: chris
lactic acid (the stuff that makes muscles feel tired after sustained exercise)

The pain felt afterwards (let's define it, in this context, as around 60 minutes after exercise has ended) is not due to lactic acid. There is nothing conclusive on the cause of it, but this article makes a good guess..

http://www.active.com/mountainbiking/Articles/It_s_not_about_the_lactic_acid__Why_you_re_still_sore_after_yesterday_s_ride.htm

The pain felt immediately afterwards is due to lactic acid, sure, but since it clears out in under an hour, it cannot be responsible for sustained pain. Is this what you meant?

 

Offline rebeccaspears

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Re: Do red blood cells (erythrocytes) contain mitochondria?
« Reply #8 on: 23/11/2015 11:02:53 »
In humans (and all mammals), red blood cells lack mitochondria and therefore has no functional TCA cycle. They metabolize glucose mainly via glycolysis, forming lactate which is released from the cells; this yields 2 ATP for each glucose molecule, much less than complete oxidation (ca 30 ATP), but enough to support the red blood cells' energy needs.
 

Offline puppypower

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Re: Do red blood cells (erythrocytes) contain mitochondria?
« Reply #9 on: 23/11/2015 12:12:28 »
What advantage does losing the nucleus and the mitochondria bring to the red blood cells? This would have been part of a selection process.
 

Offline RD

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Re: Do red blood cells (erythrocytes) contain mitochondria?
« Reply #10 on: 23/11/2015 18:34:48 »
What advantage does losing the nucleus and the mitochondria bring to the red blood cells? ...

Get rid of unnecessary components => more space for haemoglobin, and consequently able to carry more oxygen.
 

Offline chris

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Re: Do red blood cells (erythrocytes) contain mitochondria?
« Reply #11 on: 24/11/2015 07:56:04 »
What advantage does losing the nucleus and the mitochondria bring to the red blood cells?

The cells are post-mitotic and have a finite lifespan of 120 days; they do not rely on self-renewal (via cell division) but instead replacement from a supply of stem cells in the bone marrow. These requirements render the presence of the nucleus unnecessary, so I suspect that mammals evolved to eject the nucleus to make more space in the cells to make them better at squeezing through fine capillaries and hence oxygen delivery.
 

Offline puppypower

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Re: Do red blood cells (erythrocytes) contain mitochondria?
« Reply #12 on: 25/11/2015 12:49:42 »
If you get rid of the mitochondria, there is less potential for O2 to diffuse into the cell using a concentration gradient. The mitochondria use O2 as causes a concentration gradient to itself. If we get rid of the mitochondria this will keep the oxygen level higher and more even at the surface. The loss of the mitochondria also eliminates CO2 production so there is little internal driven exchange of CO2 at the surface. External interactions will more completely drive the CO2/O2 equilibrium.

 

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Re: Do red blood cells (erythrocytes) contain mitochondria?
« Reply #12 on: 25/11/2015 12:49:42 »

 

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