How many atoms are part of your body forever?

[Touring Mars]

Despite the best efforts of a couple of colleagues of mine to answer this question in the pub last night, I wasn't totally convinced that it had been answered fully. Simple question really, but approx. what percentage of atoms in your body are part of your body for your whole life? (By 'whole life' I mean from birth to death at an average age, i.e. about 70 years old.)

My friend was trying to convince me that everything in the body regenerates at different rates... but I was trying to explain why things like tattoos can and do stay on your skin forever, or (in my case) the stain left by a graphite pencil when I accidentally stabbed myself in the hand while checking my Dad's football coupon one Saturday afternoon when I was a kid... I can still see the mark in the middle of my hand, leading me to surmise that those atoms that go to make up that spot on my hand are the same atoms that were in my hand when I was a child, or is that completely wrong...?

 

[niky]

I have the same graphite stain stuck under my skin from a similar childhood incident, although time has leached much of the carbon out of that stain.

I think we can safely say that much of the atoms in your bones and teeth will stay with you forever. Not sure about everything else. Say about 50% of your bone material is permanent... though most of it is not from birth, since our bones calcify as we age, we can count that out. Atoms in hair are permanent, but the hair itself isn't.

Neurons don't regenerate after a certain age, so most of the neurons you have when you leave college will stay with you till you die... but how much of their component atoms will stay with you forever? 30%? 50? I think the DNA in the nucleus of neurons is permanent (hence, permanent atoms), as it's unrepairable.

At birth, we weigh something like 3-5% of what we do when we're 20. So the answer can't be greater than 5%. The most you can say is that a newborn's cells are permanently part of your body, but that their component atoms may change over time and damage... I'd say maybe 1-3% of your death weight will be atoms that have been with you from birth.

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RE: the atoms that make up that spot on your hand. The Cells are continually regenerating at the surface, but subdermally, and in the muscle tissue, the process is slow, and many of those cells will be there till you die. Tattoos do fade over time... The atoms in the DNA fragments that are transferred from cell to cell should be permanent, as part of aging is DNA-decay (I believe).

 

[Danoff]

I agree that the percentage is probably quite low given that very little of your eventual self exists at birth. But if you were to ask "how many atoms from your body at age 20 will be with you until you die", the percentage would go much higher.

 

[skip0110]

The atoms in the DNA fragments that are transferred from cell to cell should be permanent, as part of aging is DNA-decay (I believe).

In a new cell, isn't the DNA manufactured from other atoms in food you ate?

When a cell duplicates (mitosis), each cell gets 1/2 a DNA helix from the original cell, and the other half is assembled from free nucleic acids in the cell. DNA decay happens when the copying process has errors that compound over time. (I think)

 

[Famine]

I have the same graphite stain stuck under my skin from a similar childhood incident, although time has leached much of the carbon out of that stain.

I think we can safely say that much of the atoms in your bones and teeth will stay with you forever. Not sure about everything else. Say about 50% of your bone material is permanent... though most of it is not from birth, since our bones calcify as we age, we can count that out. Atoms in hair are permanent, but the hair itself isn't.

Neurons don't regenerate after a certain age, so most of the neurons you have when you leave college will stay with you till you die... but how much of their component atoms will stay with you forever? 30%? 50? I think the DNA in the nucleus of neurons is permanent (hence, permanent atoms), as it's unrepairable.

At birth, we weigh something like 3-5% of what we do when we're 20. So the answer can't be greater than 5%. The most you can say is that a newborn's cells are permanently part of your body, but that their component atoms may change over time and damage... I'd say maybe 1-3% of your death weight will be atoms that have been with you from birth.

----

RE: the atoms that make up that spot on your hand. The Cells are continually regenerating at the surface, but subdermally, and in the muscle tissue, the process is slow, and many of those cells will be there till you die. Tattoos do fade over time... The atoms in the DNA fragments that are transferred from cell to cell should be permanent, as part of aging is DNA-decay (I believe).

I think you're muddying the definitions of cells, molecules and atoms.

A neuron is a cell. DNA is a molecule. Carbon is an atom.

While a neuron may be fixed at a certain age, the molecules that make it up are continually changing and being refreshed - the proteins in it continually form and denature, the lipids in the cell walls break down, are absorbed and reformed, the DNA in the nucleus is continually transcribed and translated into RNA and recombined by DNA polymerase...

The question is whether an carbon atom which forms, say, part of a lipid molecule in the cell wall of a retinoblast cell is the same carbon atom now as it is when you die.

And the answer is a resounding "no".


It's basically a matter of "Do we eat?" and "Do we excrete?". We take in carbon, hydrogen, oxygen, iron, sodium, potassium, lithium, calcium, sulphur and trace amounts of a few other things and poop out the same. These atoms - primarily the first three - provide us with energy and stuff to build with. Eat a carbon atom and it might spend a few weeks as glycogen, a few more as ATP, get sequestered into acetyl choline, spend a bit of time as a mycin molecule, attach itself to a T4-phage, get gobbled up by a lymphocyte, stamped into urea and then weed right out of your body.

Or burned up and breathed out.

That notwithstanding, atoms are subject to change themselves - one stray neutrino strike and a carbon-12 becomes a nitrogen-12, knackering up the molecule it was in at the time. About 3 million neutrinos pass through each of us every second.


So I'd say that about almost-none of the atoms in your body were there when you were born and remain there until you die.



Tattoos confuse me, because I just don't get skin cells. Your whole skin is changed once a month - so why do tattoos and moles stay behind?

 

[daan]

The question is whether an carbon atom which forms, say, part of a lipid molecule in the cell wall of a retinoblast cell is the same carbon atom now as it is when you die.

Strangely, I was just going to ask that very same question.

 

[Famine]

On the tip of your tongue...

Oooh. Electrons. Atoms chop and change electrons all over the shop - bonding and becoming ions. Is a carbon atom with 6 completely different electrons still the same carbon atom?

 

[Danoff]

Tattoos confuse me, because I just don't get skin cells. Your whole skin is changed once a month - so why do tattoos and moles stay behind?

Your body certainly isn't replenishing the ink in the tattoo, so it must be the same atoms in the tattoo.

 

[Famine]

Your body certainly isn't replenishing the ink in the tattoo, so it must be the same atoms in the tattoo.

And moles?

Moles confuse me.

 

[Danoff]

And moles?

Moles confuse me.

Maybe the moles are replenished... hey I don't know. Are tumor cells replenished? They must receive nutrients or they'd die.

 

[Sage]

And moles?

Moles confuse me.

Oh dear, I’ve been studying Chem too much – I thought you saying you were confused by 6.022×10^23.

 

[daan]

On the tip of your tongue...

Was I part of a joke there?

Your body certainly isn't replenishing the ink in the tattoo, so it must be the same atoms in the tattoo.

Maybe they're chameleonic atoms that take on the same pigment as the atom it replaces. 💡

 

[Famine]

Maybe the moles are replenished... hey I don't know. Are tumor cells replenished? They must receive nutrients or they'd die.

Yes/no.

Tumours less than the magic 2cm don't receive nutrients directly. Tumours more than 2cm have already subverted the blood supply for their own needs (otherwise the cells in the middle will start to necrose) and will receive nutrients and shed cells.

 

[UnoMOTO]

When you look at a person's tattoo, you're seeing the ink through the epidermis, or the outer layer of skin. The ink is actually in the dermis, which is the second layer of the skin. The cells of the dermis are far more stable than the cells of the epidermis, so the tattoo's ink will stay in place, with minor fading and dispersion, for a person's entire life.

linky

 

[Barracuda]

I don't know half of the stuff you guys are talking about ( im only in biology ) but what about the atoms in the cells that make up your heart and other essential internal organs?

 

[Famine]

I don't know half of the stuff you guys are talking about ( im only in biology ) but what about the atoms in the cells that make up your heart and other essential internal organs?

They're replaced too.

Not wholesale, obviously...

 

[Dave A]

Unless you get a heart transplant 💡.

 

[niky]

Oh, so if DNA is continually being re-transcribed, it can't be permanent. I wasn't trying to muddy it up, but I was trying to figure out if any structures in the atoms were permanent (carried over over time), then it might be possible for the atoms that compose them to carry over... apparently not... 👍

I guess nothing from birth is permanent, or the percentage is so small as to be insignificant.

But from twenty, there's lots... calcified bones, teeth... got to count for something, right?

 

[Famine]

Oh, so if DNA is continually being re-transcribed, it can't be permanent. I wasn't trying to muddy it up, but I was trying to figure out if any structures in the atoms were permanent (carried over over time), then it might be possible for the atoms that compose them to carry over... apparently not... 👍

I guess nothing from birth is permanent, or the percentage is so small as to be insignificant.

But from twenty, there's lots... calcified bones, teeth... got to count for something, right?

The structures are permanent and, in some cases, the cells are too, but the molecules that make up the cells are in constant flux and the atoms that make up the molecules even more so.

 

[Touring Mars]

And the answer is a resounding "no".

Tattoos confuse me, because I just don't get skin cells. Your whole skin is changed once a month - so why do tattoos and moles stay behind?

Nice explanation 👍 and this is pretty much what my mate was saying the other night, but we still got stuck on the tattoo bit as well... I reckon there must be some types of structures, like moles, and some types of molecules (like foreign bodies, tattoo ink etc.) which are highly stable and remain in the body forever once they are there, but that begs the question, what other types of structures hold on to their basic building blocks as well, like bones, teeth etc.?

Although, there is the additional point that even if everything is in a constant state of flux and renewal, even if a tiny percentage of atoms happen to survive every time, there is still going to be a very large amount of individual atoms that never leave your body (simply by chance). Even the amount of atoms in a single strand of DNA from your mother and father may still account for some of the atoms in your body right now too... (although I'm not so sure about that, but it is possible)

 

[kennythebomb]

This is a really fascinating discussion! I wish I could contribute more than just saying I enjoyed reading it.