July 01, 2007

Sperms: On Her Majesty's Service

sperm showing head, body and tailNo, I am not talking about a James Bond movie. But nonetheless, this agent I am referring to is no less smart than the fictional agent. Truth is stranger than fiction, sometimes!

Sperms, which originate from the testes, are tiny motile cells, which propel themselves up through the female genital tract, to meet the ovum. This journey is not dissimilar to that of a guided missile like the stinger missile, which twists and turns in its sojourn, following a trail of heat, left behind by its target. Sperms, likewise, latches onto odorant molecules liberated by the ovum, using its hi tech olfaction system, to chase the scent of a woman.

On its head it has a 'warhead' comprising of DNA, a vast storehouse of information, so miniaturized that even modern day data compression systems would marvel at it. It dictates the ovum about how the progeny (offspring) would look like- its ethnic characteristics, skin color, gender attribute, susceptibility to diseases like cancer, hypertension, diabetes and even AIDS.
Carrying this cornucopia of database, the sperms swim the 'gulf' with the agility of a swimmer.

The energy for this is provided by the plentiful ATP (adenosine tri phosphate molecule) prepared by mitochondria that are abundant in the sheath of the sperm. The sperms also produce a molecule, 'CatSper', which functions as a calcium ion channel, permitting calcium ions to enter the tail of the sperm. This protein is produced in the principal piece of the sperm and is responsible for the final push it needs to reach its goal (quite like the last stage booster of a rocket). It ('CatSper') is presently the target of contraceptive research, as disabling this molecule will also disable the molecular motors (there are 11 microtubules in the sperm which are crucial for its motility, and they are Ca+ dependent), thus freezing the sperm on its sojourn. New ideas about sperm motility are beginning to emerge.

Sperms supposedly contain a huge load of protons (H+, hydrogen ions). These positive charges are more likely to come out to an environment that has LESS positive charges, as the concentration and electrical gradient will be more favorable. The flow of protons will produce a current, and this current will boost pump the sperm motility. The sperms get a speed boost in the high pH (=low H+, high alkalinity) of the vagina and the fallopian tube. A channel, called Hv1 senses the voltage difference, and when open, causes the exodus of protons from inside the sperm. Zinc inhibits the channel and keeps it closed. In the female genital tract, zinc dissolves. This leads to un-guarding of the protons. Ganja (cannabis) smokers supposedly overuses this channel, which is sensitive to endocannabinoids, and thus burn the sperms. Infertility in marijuana smokers may thus be explained.

Regarding the chromosomes within the sperm it needs be mentioned that the number is exactly the half of that of autosomes. Thus they contain 23 chromosomes. This means that after combining with the ovum which also have 23 chromosomes, the total tally will be 46. The zygote that forms will thus have 46 chromosomes and by the process of mitosis the fetus will inherit 46 chromosomes: half from the sperm (father) and rest half from the ovum (mother).

The number of the chromosomes are cut into half by a reduction division called meiosis, which occur in the gonads (testis in male, ovary in female). During meiosis, not only there is halving of the number of the chromosomes, but also there is this much needed "re-assortment" of them by "chiasma formation". This genetic interchange (by chiasma formation) accounts for evolution, differences among siblings, propensity to different diseases and many others.

Thus it is not very hard to imagine why I call them the smartest cells. You may give your vote to the neurons or the cardiac pacemakers, but I have my own reasons, you see. By the way, the ovum is a close contender, but it can NOT move. At the same time, there's no denying the fact the way it (ovum) raises a firewall kind of stuff, once it has been fertilized by a sperm, so that another sperm do not penetrate it again.
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