May 14, 2016 at 01:47AM

Yesterday I Learned: 1) Old thermal cyclers are huge because they're basically little refrigerators! Refrigeration means a pump, and some kind of effective form of heat dissipation. That means size. (Also, in case you didn't know, modern thermal cyclers use Peltier coolers, which are AMAZING devices that transfer heat the way a refrigerator does, but does it by applying electric current through a relatively small metal block. I honestly don't understand how the physics works, but the upshot is that they're small, light, and have no moving parts. The disadvantages are that they're expensive and not very power efficient.) 2) There's a eukaryote without any trace of mitochondria! It's called Monocercomonoides sp. PA203, and it's a single-celled, flagellated parasite, and by all rights, it really ought to have mitochondria. But it doesn't. Firstly, it's interesting how we know they don't have mitochondria -- we don't think they have mitochondria because they don't have any of the usual genes associated with them. That's a kind of odd way of telling if there are mitochondria... but it also is probably the most definitive way of doing so. If you look at them under a microscope, it's really hard to tell mitochondria apart from other organelles (and if you use a mitochondria-specific dye to mark the mitochondria and you don't see anything, it's hard to know if they actually don't have mitochondria or if they just don't stain the usual way). How does Monocercomonoides survive without mitochondria? Well, firstly, it doesn't seem to breathe oxygen -- all of the usual genes for aerobic respiration are missing, and it has an expanded set of anaerobic metabolic enzymes. That's the big thing that makes mitochondria necessary, but not the only thing -- apparently mitochondria are also critical for forming the iron-sulfur complexes used in iron-sulfur proteins... which are mostly used for aerobic respiration anyway, but apparently are necessary even without a mitochondria? Anyway, Monocercomonoides gets by using a set of four *bacterial* iron-sulfur complex formation genes. This isn't the first time this particular set of genes has been seen in a eukaryote, and the genes have introns in them, so they're not just bacterial contamination. Some of you out there have heard me claim that there really isn't gene transfer between bacteria and eukaryotes -- this is where I eat my shoe. Another important point the authors make is that this is likely the result of a *loss* of mitochondria at some point in the organism's past (which is awesome and strange) rather than a eukaryote that never had mitochondria in the first place (which would immediately make it one of the most important evolutionary findings of the modern era). How do they know? Well, they don't, but it's HIGHLY suggestive that a) every single one of this species' close relatives has mitochondria and b) all of those species (including PA203 itself) are parasites of animals. It's not particularly plausible that the only living eukaryote descended from pre-mitochondrial eukaryotes happened to evolve animal parasitism in parallel with all of its once-close relatives.... One question I have -- can these critters apoptose? As single-celled parasites, they may not need to, but I'm curious to know if they've evolved another way to do it. Now, bear in mind that all of the above comes from a hot-off-the-press Cell article, which in and of itself means it's more likely to be awesome (check) and more likely to be falsified in the next year (time will tell) than your average publication-in-a-decent-journal. So we'll see. Thanks to Asher Rubin for alerting me to this story! 3) Circadian rythems are more strongly affected by external purturbations at some points in their cycles than others. Unfortunately, the only data I've seen on this so far is from a cyanobacteria, so I have no idea how to apply this to human sleep cycles. (Another good fact to know -- most circadian rythems function normally for about 24 hours without any external signal before they fall apart.)