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December 20

Control of mitochondrial gene expression

The mitochondrial genome is circular plasmid (prokaryotic in origin) while the eukaryotic genome is linear. Are there well-known mechanisms by which the eukaryotic nucleus turn individual mitochondrial genes on and off and exert transcriptional control on the circular mitochondrial genome? When cancer cells inhibit mitochondrial activity, would they for example, just repress the activity of POLRMT instead (on chromosome 19)? Yanping Nora Soong (talk) 02:09, 20 December 2023 (UTC)[reply]

Here is an article reviewing what is known. Summary: it is complicated. --Lambiam 20:19, 20 December 2023 (UTC)[reply]

Thank you so much! Saving this for further reading (after my exam). Yanping Nora Soong (talk) 20:39, 20 December 2023 (UTC)[reply]

Odd-indexed chemical element stability

Why does the chemical element with odd atomic number each have at most two stable isotopes? Because of the Mattauch isobar rule? Here the the term "stable isotopes" includes also the "observationally stable" ones, such as the only natural isotope of gold (¹⁹⁷Au, theoretically it should be able to decay through alpha emission). The case of potassium (₁₉K) is quite stunning as it's the only near-miss to this rule: despite that potassium-40 does decay (unlike two other natural isotopes of potassium), its half-life is very long (comparable to the Age of Earth, so long that any amount of primordial potassium-40 should have survived until now). 2402:800:63AD:E8CE:481:F5E6:57F9:5FDA (talk) 11:28, 20 December 2023 (UTC)[reply]

See Even_and_odd_atomic_nuclei. There are only 48 odd-even and 5 odd-odd isotopes overall for 41 chemical elements. So, as a rule there is only one stable isotopes for each odd numbered element. Ruslik_Zero 20:37, 20 December 2023 (UTC)[reply]

Only 40 chemical elements with odd atomic number have stable or near-stable isotopes (1 to 83, except 43 and 61), also, there may be one or two stable isotopes for each odd number of protons, the same holds for each odd number of neutrons. 2402:7500:916:185A:756A:B526:20F:B8D6 (talk) 03:24, 24 December 2023 (UTC)[reply]

It's pretty much the Mattauch isobar rule, I think. In almost all cases, odd-odd isotopes will not be anywhere near stable: the exceptions are either very light nuclides (where beta decay leads to a too lopsided proton-neutron ratio) or cases with bad spin mismatches. So if nearly all the odd-odd cases are ruled out immediately, that doesn't give you a whole lot of odd-even options; going beyond two takes you too far away from the valley of stability again. Potassium basically lucked out by having two stable odd-even isotopes ³⁹K and ⁴¹K at the middle of the valley, plus ⁴⁰K whose decay is inhibited by a spin mismatch.

When the Solar System was only a few million years old, though, Cl, Tc, La, and Bi would also have been examples, thanks to the quite stable (but not stable enough to be primordial) ³⁶Cl (note ³⁵Cl and ³⁷Cl are stable), ^97–99Tc, ¹³⁷La (¹³⁹La is stable and ¹³⁸La almost is), and ^208,210mBi (²⁰⁹Bi is almost stable). Double sharp (talk) 05:02, 24 December 2023 (UTC)[reply]

Fractions

Why fractions in unit values on Wikipedia articles cannot be used with metric units, unlike imperial units? Is a value e.g. 5 1⁄2 km unacceptable, and why? --40bus (talk) 20:19, 20 December 2023 (UTC)[reply]

That sounds like a Manual of Style issue, not a science issue? But I can easily see that because metric is intrinsically base-10, it is more self-consistent to use decimal values. DMacks (talk) 20:26, 20 December 2023 (UTC)[reply]

Because 51⁄2 km actually means 51⁄2 × 10³ m, which is a messy mixture of vulgar fraction and decimal exponential. It might work on road signs, but not in an encyclopaedia, please. -- Verbarson ^talk_edits 21:08, 20 December 2023 (UTC)[reply]

I've never heard fractions described as "vulgar" until now. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:12, 21 December 2023 (UTC)[reply]

Fuck yeah. DMacks (talk) 01:37, 21 December 2023 (UTC)[reply]

See Fraction § Simple, common, or vulgar fractions. -- Verbarson ^talk_edits 09:01, 21 December 2023 (UTC)[reply]

Vulgar fractions may be, but are not always, improper fractions.

It is more common to mix decimal exponents and fractions like this: 10^1⁄2, meaning the square root of ten. -- Verbarson ^talk_edits 09:12, 21 December 2023 (UTC)[reply]

MOS:FRAC has "Metric (SI) measurements generally use decimals, not fractions (5.25 mm, not 5 1⁄4 mm)." Guidance from NIST such as [1] uses examples with decimal points and provides guidelines for how to format decimal numbers with SI units. It does not have any examples or recommendations for using fractions with SI units (although it doesn't explicitly say anything against it either). It does have an item 7 which aims to avoid ambiguity between mathematical operations and other symbols, which could apply here. In general, the metric system is designed to be a consistently decimal-based system, where things are always grouped by tens or divided into tens. (Our article metric system begins "The metric system is a system of measurement that is a decimal system.") Mixing it with other common fractions somewhat defeats the purpose. --Amble (talk) 22:46, 20 December 2023 (UTC)[reply]