Most vitamins and other necessary nutrients are actually pretty fundamental parts of metabolic pathways common to all life and go way back there. As mentioned, vitamin B12 is produced by cyanobacteria, which go back more than 3 billion years. It plays a role in DNA synthesis. Bacteria make most of these essential nutrients themselves; other life forms have lost the capacity.
Ok, that makes some sense. The more advanced organisms depended on the bacteria for the nutrients.
Higher organisms have lost the capacity to make these nutrients because they are expensive to make but also so easy to get from bacteria and other organisms. If you have anything like a natural diet you should get enough vitamins etc. It’s only when we are subject to highly unnatural diets that vitamin deficiencies start to show up.
If B12 is necessary for all organisms, why don’t plant foods contain significant levels of it?
How far back do you have to go before you start running the risk of organisms that have different amino acids or different DNA codes for amino acids than what life has now? Eventually aren’t you going to risk a world where the essential amino acids aren’t in existence?
Good point. I retract my statement that it is generally necessary. I don’t know why exactly animals need it but plants apparently don’t.
All life on Earth uses the same amino acids and the same DNA codes for them (with perhaps some minor exceptions). Therefore they will be present a least as far back as the origin of procaryotes (bacteria and archaea) about 3.8 billion years ago.
It’s conceivable that at some point there could have been life forms that used different amino acids and codes but no evidence of it has survived.
Of course, for purposes of us eating them, a different genetic code wouldn’t matter, just so long as they have the same aminos.
True. However mitochondria have a slightly different genetic code than other cellular organisms, and I’m wondering if you go far back enough are you in an age where amino acids that no longer exist were in use (that our body may substitute for the correct amino acids, causing deformed proteins), or the essential amino acids we can’t make ourselves and have to get from diet hadn’t become universal yet in life forms. That may be hypothetical, since there is no fossil record.
The OP said we’re assuming complete knowledge of the life available at the time we go to, and unlimited hunt/gather supplies including cooking apparatuses. So we’re not relying on being able to use our bare hands and teeth to rip apart/chew/digest raw ferns anymore than we chew up raw potatoes today. We’d know what kind of plants/animals are around, and have the means to process (cut up/cook) them at least crudely.
They have different metabolic pathways for the two reactions B12 (co-)catalyses.
Thank you. That clarifies the situation.
I’ve seen speculation (in Peter Douglas Ward’s Life As We Do Not Know It) that the earliest organisms may have had only a two-letter codon, based on clues in codon degeneracy (such as all GCs, CGs, GGs, CUs, CCs, UCs, ACs and GUs each coading for the same amino acid no matter what the third letter is.)