Wikipedia:Reference desk/Archives/Science/2019 June 1

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June 1

Great fire of Umea

In the Umea city fire, how was it possible for a line of birch trees to have stopped the spread of the fire (as opposed to propagating it)? 69.181.230.243 (talk) 01:31, 1 June 2019 (UTC)

Unless I'm missing it, that article doesn't say the birch stopped the fire. It just says more were planted after the fire. Is there a source you're getting this information from? --47.146.63.87 (talk) 02:00, 1 June 2019 (UTC)

Birch#Culture. 2601:646:8A00:A0B3:1C3:741A:FF1C:6A88 (talk) 05:24, 1 June 2019 (UTC)

It was the wide avenues that were designed to stop the fire. The birches were just decorative. I don't know how the theory arose that birch trees stop fire. I've modified the article. Should we remove or modify the "supposedly" statement in Birch#Culture? Dbfirs 08:04, 1 June 2019 (UTC)

Thanks for the clarification! 2601:646:8A00:A0B3:1C3:741A:FF1C:6A88 (talk) 01:24, 2 June 2019 (UTC)

Fission (biology)

According to that article, once chromosomes replicate "The replicated DNA copies then move to opposite poles of the cell in an energy-dependent process." How exactly is this accomplished ? What prevents, say, both copies of one chromosome from ending up in one of the cells and both copies of another chromosome from ending up in the other cell ? SinisterLefty (talk) 15:45, 1 June 2019 (UTC)

Because Microtubule of the Spindle apparatus are one-way lanes created out of each original chromosome, so each copied chromosome must move in opposite direction from the "minus" end to a "plus" end, Gem fr (talk) 17:53, 1 June 2019 (UTC)

Thanks, but what actually causes the chromosomes to move ? SinisterLefty (talk) 19:03, 1 June 2019 (UTC)

Check Intracellular transport and follow links in the article (Dynein etc.) Gem fr (talk) 19:40, 1 June 2019 (UTC)

Thanks. The molecular motor link seems to be what I needed. SinisterLefty (talk) 13:08, 2 June 2019 (UTC)

The spindle apparatus is only present in eukaryotic cells. The question is about prokaryotic fission. --47.146.63.87 (talk) 04:36, 2 June 2019 (UTC)

oups. my bad

however, previous answer still apply: the chromosome split along an axis, new copy move to opposite side in bacteria (this consume some energy, meaning: transport), then Cytokinesis occurs in some plane more or less perpendicilar to the said axis, for some reason.

Gem fr (talk) 06:04, 2 June 2019 (UTC)

Well, for one thing, the most common type of fission in biology (as opposed to the more complex mitotic division) occurs in prokaryotic organisms that only have one chromosome. So if the chromosomes don't separate one cell will have two and one will have none. The one with none is obviously not viable and the one with two probably isn't either. Thus, the problem doesn't spread. It gets even more complex in eukaryotic cells with multiple chromosomes. --Khajidha (talk) 00:39, 2 June 2019 (UTC)

I'm not sure the daughter cell with two chromosomes is nonviable. It might just divide again. Prokaryotes tend to be much less sensitive to gene dosage since, well, they're single cells: no multicellular structures to worry about. --47.146.63.87 (talk) 04:36, 2 June 2019 (UTC)

It would have to live and grow before it would be large enough to divide again. I'm not sure how much the double dosage of DNA would affect a prokaryote, but I've never heard of it being observed so I am reasonably comfortable with the idea that it would be less than optimally functional. --Khajidha (talk) 04:56, 2 June 2019 (UTC)

Quite likely! It might also give rise to interesting mutations. --47.146.63.87 (talk) 05:09, 3 June 2019 (UTC)

Most prokaryotes only have one circular chromosome. If both chromosomes wind up in one daughter cell, the other will have no DNA and just die. This presumably happens sometimes, as nothing in biology is foolproof: the eukaryotic equivalent is chromosomal nondisjunction, responsible for many chromosomal defects. As to the question of what in the cell is responsible for separating the chromosomes, good question! The article says, unsourced: The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane. Further down, it says: The replicated DNA copies then move to opposite poles of the cell in an energy-dependent process, citing [1], but that article appears not to be talking about DNA replication at all. It's talking about bacteria sequestering protein aggregates during division. This source I found from a Web search mentions FtsZ, which we happen to have an article about, but that's involved in forming the ring structure that splits the cytoplasm, not in moving the DNA. --47.146.63.87 (talk) 04:36, 2 June 2019 (UTC)

to ensure that each new cell has a copy, the fission (new cell wall building) just need to occur somewhere between the two chromosome (or their attach point to the membrane, in case of prokariotes), which is easy and quite natural even without any special apparatus. Gem fr (talk) 06:31, 2 June 2019 (UTC)

Cells don't rely on just sitting and waiting for things to randomly float around. The interior of a cell is quite crowded and busy. Model drawings that show cells as just a big blob of cytoplasm are omitting most of the cell's contents. --47.146.63.87 (talk) 05:09, 3 June 2019 (UTC)

Our article on chromosome segregation addresses the topic here, but is primarily focused toward eukaryotes. (Note that fission (biology) addresses both prokaryotes and eukaryotes, and I'm not sure which you want. Their citation on prokaryotes, though, is very interesting: this article talks about the separation of the dividing DNA into "protonucleoids" while the DNA is still only partially divided, in the sense that the process begins at an origin of replication and continues throughout the entire circular bacterial chromosome. Note though that bacteria replicate so fast that the daughter pronucleoids can have begun their DNA replication before the parent cell is finished! I don't know this story, so I should shut up and read the paper. Wnt (talk) 20:39, 2 June 2019 (UTC)

Reminds me of Tribbles, since, according to Leonard McCoy, "They're apparently born pregnant, which seems to be quite a time-saver". :-) SinisterLefty (talk) 04:47, 3 June 2019 (UTC)

This actually happens in some animals. Mother Nature can get pretty gnarly. --47.146.63.87 (talk) 05:09, 3 June 2019 (UTC)