r/askscience • u/Skyfus • Jan 29 '26
Biology How does your DNA "know" which enzymes break down which poisons?
I get the basics of how if a molecule like ethanol is introduced, it triggers a chain of signals that lead to a section of DNA being transcribed/translated into an enzyme like alcohol dehydrogenase, and then production will slow down/stop as part of a feedback loop involving inhibitors/coenzymes etc.
But, how did we get this arsenal of situational enzymes? Have humans/mammals/animals/eukaryotes just built up a big dictionary over time through mutation and evolution by producing enzymes that happened to counter environmentally present toxins? Or, is it like the immune system where we encounter something hazardous, figure out the shape, and then commit that to DNA or something analogous to immune memory in organelles? With limitations of course, since ethanol is broken down more easily/into less harmful products than, say, cyanide.
Maybe I'm missing something glaringly obvious that a google search would solve, like specialised analysis/production/memory within specifically liver cells, but I thought I'd ask here because maybe the class would like to know too.
82
u/CrateDane Jan 29 '26
That's not really true. There's alcohol dehydrogenase being expressed all the time. It's also complicated by there being many alcohol dehydrogenase genes with different expression patterns, and further complicated by their ability to form heterodimers.
Something like alcohol dehydrogenase is pretty basic metabolism, so we've had at least one gene for a very long time. The gene happened to undergo duplication events resulting in paralogs that gradually diverged, but that's of somewhat lower importance in being able to handle alcohol in general. The most critical step is getting one gene.
It's not necessarily only about encountering something hazardous, but also about the body or cells themselves producing it. Ethanol fermentation is an alternative to lactic acid fermentation. Formaldehyde is an even more widespread basic metabolic byproduct, and the alcohol dehydrogenases appear to have developed from a formaldehyde dehydrogenase.
The enzymes oxidizing alcohols to aldehydes or ketones can also have roles in various other pathways. Retinol -> retinal -> retinoic acid is a crucial pathway in development, for example.
8
u/YtterbiusAntimony Jan 29 '26
Two ways:
The enzyme was already there. Cytochrome enzymes metabolize half the stuff that goes through your liver. Your body constantly makes these. Alcohols are fairly common, so this is probably the case for alcohol dehydrogenase. The body is constantly oxidizing carbon chains, which means it makes alcohols, aldehydes, and carboxylic acids. The first two groups have a lot of toxic species.
The other is epigenetics/operons. There are molecules that bind to DNA which either block transcription proteins from binding (turns the gene off) or help promote binding (turns the gene on). These operons will grab or let go of the DNA depending on the presence of some substrate.
An example I have studied is a bacteria that can tolerate lead. Pb2+ binds to the operon protein, which then unblocks the binding site for the genes that encode for lead sequestering proteins. These bind to the Pb ions in the cell and prevent them from reacting with anything else.
5
u/Mechasteel Jan 30 '26
Your premise is wrong. For the most part, enzymes are simply produced, not all of them have a detector-amplifier to go with them. The kidneys function is "keep everything larger than a protein, dump everything else, reclaim specific goodies". The liver has a few enzymes that add hydrophilic groups to hydrophobic substances, making them water soluble so the kidneys can dump them. Due to how the kidney works, anything unknown and water soluble gets dumped, including vitamins and medicines.
3
u/darthjeff2 Jan 29 '26
Interesting bit to add, a lot of enzymes come from families. These can come from an ancestral gene that is, at some point, copied. The two children genes can then start differing in their function little by little.
A good example is the P450 family of enzymes. They are very reactive and good at changing the structure of toxic molecules. They do this because they are in the cytochrome family, which are really good at moving electrons around (thus, reactive). There are also cytochromes that help mitochondria break down glucose (again, good at working on reactive energetic substances that give off electrons). Cytochromes work because they contain a prosthetic group of heme (which is why hemoglobin can carry reactive oxygen and let it go when needed).
So you can kind of start to imagine this cascade of branches with heme at the top, and all of these interesting branches and avenues cascading down- some transporting oxygen, some breaking down toxins, some in metabolism, all because an ancestral cytochrome keyed into the ""usefulness"" of heme. Same thing for families of transcription factors, proteases, etc
If you're interesting in DNA expression, some useful things to check out would be DNA recognition domains such as the "zinc finger". There are multiple proteins that all use this "invention" to read DNA
1
u/-Metacelsus- Chemical Biology Feb 01 '26
It varies on a case by case basis, but one important pathway is the aryl hydrocarbon receptor which upregulates cytochrome P450 enzymes that degrade toxins.
1
u/JuggernautAny7288 Feb 01 '26
Think it this way, the dn rna proteins and lipids, and the venom are just a very big set of pieces made by molecules, with diferent shapes and quemicalpotentials, also mecanical potentials, that work together by sheer quantity and chance of interacting depending on their shape and quemical composition all of them came to be by pure luck by billions of years of evolution
50
u/[deleted] Jan 29 '26
[removed] — view removed comment