Wikipedia:Reference desk/Archives/Science/2018 December 23

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December 23

Most abundant molecule

What is the most abundant molecule in the Universe? DroneB (talk) 14:38, 23 December 2018 (UTC)

It doesn't say so outright at Hydrogen#Natural_occurrence, but hydrogen gas (H2) seems a good bet. Gråbergs Gråa Sång (talk) 16:19, 23 December 2018 (UTC)

We have an article called Abundance of the chemical elements, and broadly introduces the ideas that help us understand why hydrogen is so common. Elements in our universe can exist as molecules, individual atoms, or as ions; our article on the universe broadly introduces these concepts.

Broadly, hydrogen exists as ionized hydrogen, atomic hydrogen, molecular hydrogen, and hydrogen bonded to other chemical elements in larger molecules.

Most of the hydrogen in our universe is monoatomic or ionized.

For an authoritative reference, consider finding a copy of Planetary Sciences.

Nimur (talk) 16:37, 23 December 2018 (UTC)

Water is the most abundant triatomic molecule. Dihydrogen H₂ would beat it in number, but there is also dihydrogen cation H₂⁺, a common ion. Graeme Bartlett (talk) 12:03, 24 December 2018 (UTC)

How bout what's the most abundant compound in the world, rather than in the universe? For gases - N2 gas, and foe liquids, H2O. I don't think it's readily obvious are there more N2 molecules or H2O molecules? And what would be the 2nd most abundant liquid after water? Thanks. 67.175.224.138 (talk) 02:54, 26 December 2018 (UTC).

Consult our article: Abundance_of_the_chemical_elements#Earth.

The most abundant liquid on our planet is surely iron in the outer core. Iron makes up 30% of our planet, by mass; compared with about 0% of our planet that is water.

If this is a topic of interest, it's generally covered in great detail in any good textbook on geology or planetary science. Are you looking for such references? A good starting place is our article on Geology.

Nimur (talk) 16:40, 26 December 2018 (UTC)

The original questioner asked about the Universe. On Earth there would be far more water molecules than nitrogen. Just think of the difference in air pressure versus water pressure, and a water molecule is lighter than a dinitrogen! Also liquid iron is not in the form of molecules. Carbon monoxide is also common in the universe. The H₂ molecule is hard to detect as it is transparent to light, and as it has no dipole it is also very faint in microwaves. So carbon monoxide is often used as a proxy to explore molecular clouds. Stars can also contain molecules but our article is too basic yet to indicate what is the most common, but OH and CH are combinations of common elements. Graeme Bartlett (talk) 23:47, 26 December 2018 (UTC)

Is the action potential in the heart longer than the neuron because there are less ion channels, or because each ion channel is slower?

Try as I might to try to find an equivalent of a "catalytic efficiency" or even a kcat for hERG, Kv1.1, Nav1.1, I just get voltage clamp studies involving conductivity normalized for cell surface area but not the amount of protein. What keyword do I need to use differently? The total permeability of the hERG potassium in the ventricle is 340 pS/pF (Wilson and Marrion et al. 2016), whereas it is ~25000 pS/pF in the neuron -- is this due to decreased expression in the heart OR an intrinsic property of hERG? I don't get why so many studies don't address this obvious issue. Yanping Nora Soong (talk) 15:05, 23 December 2018 (UTC)

Solved this issue. For those interested in the answer, I compared single-channel current recordings for hERG (Vijayvergiya et al. 2015, Biomed Devices 17:12) and KCNA1 (Hao and Padilla et al. (2013) Neuron 77:899-914). hERG may have slower activation and deactivation kinetics than KCNA1 and also have lower peak permeability in the neuron but it is actually more efficient at passing potassium current channel for channel (1.1 pA / channel @ 0 mV for hERG versus 0.78 pA / channel @ mV for KCNA1). Neurons must just simply express a very very high amount of potassium channels. Yanping Nora Soong (talk) 16:57, 23 December 2018 (UTC)