Recent comments in /f/askscience

CrateDane t1_j9267og wrote

Reply to comment by agate_ in Why does the thyroid use iodine ? by geistererscheinung

> > > > > What animals have a thyroid?

Vertebrates. Invertebrate chordates have an organ called the endostyle, which has some functional similarity and is very likely the evolutionary predecessor to the thyroid gland.

> Is iodine chemistry localized in a different organ in the ones that don’t?

Well... many aquatic invertebrates may rely mainly on exogenous thyroid hormones, so they don't need an organ for it. Other invertebrates may have their own endogenous production of thyroid hormones, but without a dedicated organ. Yet other invertebrates, particularly outside the bilaterians, may be less reliant on thyroid hormones in the first place, since they seem to lack an ortholog of the thyroid hormone receptor.

Here is an interesting review article about thyroid hormone signaling in invertebrates.

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isaacwoods_ t1_j925jbo wrote

Reply to comment by agate_ in Why does the thyroid use iodine ? by geistererscheinung

It’s precisely because elemental iodine is very reactive. The thyroid has follicles, where iodine is pumped into a gel in ion form, and then enzymatically converted into elemental iodine, where it then attacks thyroglobulin to create thyroid hormones. The final hormones are the only molecules allowed out of the follicular lumen back into the blood.

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Minothor t1_j925704 wrote

Reply to Will a sheet of paper go brown with age over the decades if kept in a dark waterproof container? by west_ozzie

It depends on the chemistry used in the process, amongst other things, but probably not.

Regarding the chemistry - older (and some sulphur based modern) methods of bleaching left mildly acidic residues in the page and these caused the paper to brown over time, accelerated slightly if the paper had been exposed to the fatty acids in sebum from people's skin.

Newer methods supplement bleaching with a filler material such as calcium carbonate, partly to reduce the wood pulp required, partly to reduce the amount of treatment required to achieve a white product at the end of the day.

Pages produced in this way have little, if any acid residues and should remain white for a much longer period of time, I doubt if it would do so indefinitely though - oxygen in the air, microbes on the surface or other factors could result in slow degradation and discolouration over time.

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agate_ t1_j921et4 wrote

Reply to comment by Bbrhuft in Why does the thyroid use iodine ? by geistererscheinung

This is a neat answer, but I hope someone will tackle what I think is the most interesting part of OP’s question: why is iodine biochemistry apparently localized in the thyroid? It’s not like we have specific organs for zinc or manganese chemistry. (Or do we?)

What animals have a thyroid? Is iodine chemistry localized in a different organ in the ones that don’t?

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Snoo-76025 t1_j91hbcl wrote

Reply to Why does the thyroid use iodine ? by geistererscheinung

Its just one of the trace elements (among cobalt, copper, zinc, chromium, flouride etc for various other specialised mechanisms) that the life forms on earth have evolved to utilise for specific purposes. Its very hard to 'exactly' trace back the evolutionary mechanisms for specific metabolic pathways in highly evolved creatures and be sure that a particular narrative is the only one.
I know it kinda doesn't answer you question exactly. Life just used and incorporated whatever chemicals (in roughly the same proportion) were available in the environment around them.

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Bbrhuft t1_j91bx8b wrote

Reply to Why does the thyroid use iodine ? by geistererscheinung

It's a bit of a mystery. However, the evolutionarily roots of iodine cell signalling is very acient, almost all all multicellular life uses iodine containing molecules, including plants.

A recent interesting hypothesis proposed that... Given that almost all multicellular life uses iodine containing cell signalling molecules, they must have evolved very early billions of years ago in early single celled organisms, and the development of multicellularity and iodine containing cell signalling molecules went hand in hand.

The reason why iodine was used, is that molecules that contain iodine are highly reactive and often powerful antioxidants, they are very useful.

Crockford, S.J., 2009. Evolutionary roots of iodine and thyroid hormones in cell–cell signaling. Integrative and comparative biology, 49(2), pp.155-166.

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grumble11 t1_j9188om wrote

Reply to Why does the thyroid use iodine ? by geistererscheinung

Iodine is in seawater so was part of the environment of early life. This meant that evolution incorporated it into its core chemistry - it was always around. As animals arose on land some areas were iodine deficient but the element was firmly in biology by then

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