Spermine (DNA Packing Material)
15th June 2006
One thing they touch on in biology class but never really get into is the fact that DNA is wound up into a tight little structure in the nucleus of eukaryotic cells, as well as sperm. Just how the cell gets the DNA to cooperate isn’t really explained. DNA is a polyanion - that is, it has a repeating negative charge.
Since it has all these negative charges, it’s a bit difficult to coil DNA up into a tight structure (since, you’ll remember, like charges repel). Cations can help with this. Metals can do it; without the salts in your cells, your DNA wouldn’t stick together as well. Today, though, I want to talk about sperm, and sperm use the aptly named oligoamine “spermine” as well as another, “spermidine”:
At physiologic pH, spermine is protonated (the lower form shown above, maybe one proton less). These cations interact with the negative charges along DNA and can help them pack nicely. Spermine is a pretty low molecular weight amine. These all tend to stink pretty badly. Here are some of the more common (and colorfully named) low-MW amines:
Putrescine and cadaverine are products of decomposition, and, I am told, smell of rotting flesh. As you might image, spermine and spermidine smell like, well, essence d’semen. Also (perhaps more) relevant to DNA packing in sperm are the protamines, a series of proteins. In chromatin, the corresponding proteins are the histones. Unsurprisingly, these proteins are also rich in positive charges. DNA in sperm and non-germ cell nuclei is wound about these proteins. The spermine et al no doubt contribute to the concentration of cations present, which helps DNA pack more nicely, but they have also been invoked as a sort of endogenous biological buffer. The vaginal environment, you see, is a bit acidic (less than pH 5, or more than a hundred times the proton concentration in blood), and it’s suggested amine-based buffering gives the poor swimmers a chance. In its parsimonious way, though, nature never gives a free ride, and it’s been suggested that some yeast infections are caused by the basic species present in semen. This putative pH disruption allows unfavorable yeasts to predominate over the natural (favorable!) bacteria present.
That’s it for today, see you tomorrow!
June 15th, 2006 at 10:38 pm
Hehehehe. Sperm.
I’m not a biologist, but you’ve explained this in a way that I can understand. Thanks
June 18th, 2006 at 10:26 pm
very interesting..
June 27th, 2006 at 10:56 am
The thrust of this comports with what I have found in my reading. I also take it that spermine and spermidine are loads of olfactory fun in the lab. Thanks for giving the public a chemist’s penetrating insight in a lay-accessible explanation. I shall most probably swallow the bait and blog this myself rather soon; looking ahead further, this area is fertile ground for research by a science-lover cum sex-scholar such as I.
Analogously, I have also been looking to find information on the divers interesting compounds in vaginal fluid—particularly what gifts it with its physical, biochemical, and aromatic properties[*]. Wikipedia yields the following list: “water, pyridine, squalene, urea, acetic acid, lactic acid, complex alcohols and glycols, ketones, and aldehydes” Without further elaboration or appropriate citations, I take it with a crystal of sodium chloride.
Nonetheless, I’d really like to know what “complex alcohols and glycols” they are talking about, as those (along with squalene) are where I’d look first for the slippery magic. Might the likes of glycerol or propylene glycol perhaps be involved? IIRC, those are both ingredients in Astroglide (c.f. K-Y Jelly, which as you covered the other day, contains carboxymethylcellulose—probably glycerol too, from its taste). As for pyridine, if that is correct, I hypothesize we have found the source of many puerile jokes.
I have also heard that vaginal secreta may contain compounds which interact with spermatozoa in interesting ways less obvious than the hydrogen activity effects mentioned above. However, I shan’t speculate before I hit the books and read up. Search “human sperm competition” for details.
[*] Aromatic as in scent, and aromatic in the benzene-chemistry sense, per pyridine and the like. Sweet and sour!