Fürkész

An Electronic Clue In The Mystery of DNA Repair

Source: http://www.technologyreview.com/blog/arxiv/24420/

“DNA repair machines may home in on the electrical signals created by mutations.

DNA is regularly damaged by ordinary wear and tear and the constant buffeting of ionising radiation. However, cells possess an extraordinary collection of molecular machines such as repair enzymes that rapidly identify the defects and repair them.

The puzzle is how they do it. One idea is that repair enzymes simply float about for long enough and eventually find damaged regions. But the numbers just don’t stack up. Genes are usually between 1000 and 1,000,000 base pairs long. By contrast, a typical mutation usually involves just a handful of base pairs. That’s just too small to find using a random walk with any reliability. Some other form of active location finding must be going on.

One theory is that mutations change the electrical characteristics of a stretch of DNA and that this creates a signal that repair enzymes can home in on, like electricians locating a break in a circuit. The trouble is that DNA doesn’t conduct electricity like a power cable and so it isn’t clear how this would work.

Now Arkady Krokhin at the University of North Texas and few buddies have worked out how DNA may do it. The key turns out to be that different regions of DNA have different electrical characteristics. The group has calculated from first principles the way in which charge flows in different regions. They say that in exons—the information carrying parts of genes—the energy spectrum of the molecule allows delocalised electrons to exist. In these areas, charge can flow.

However the energy spectrum of the regions that do not carry information—the introns—does not allow for delocalised electrons. So introns are effectively insulators.

That sets up well defined regions within DNA that can be identified electronically.It also means that any change in electronic properties caused by a mutation would be largely confined too. That immediately suggests a way that repair enzymes can home in on damage.

Of course, this work is just one step towards a coherent theory that explains DNA repair (which actually involves many different processes).

But the beauty of this approach is that it could also explain why some damage goes unrepaired, leading to cell death and even cancer.

The thinking is that certain mutations cause less of an electrical change than others. These mutations are “electronically masked” and so go undetected by repair enzymes. There is even experimental evidence for this from resistance measurements done on DNA with cancer-causing mutations.

If this theory is true, one important question is how might it be possible to exploit DNA’s electrical characteristics to detect and even prevent cancer in future?”

Ref: arxiv.org/abs/0911.2953: Inhomogeneous DNA: Conducting Exons And Insulating Introns

Did you know that fruit bats are the only non-primate to engage in oral sex?

Source: PLoS ONE: Fellatio by Fruit Bats Prolongs Copulation Time

Oral sex is widely used in human foreplay, but rarely documented in other animals. Fellatio has been recorded in bonobos Pan paniscus, but even then functions largely as play behaviour among juvenile males. The short-nosed fruit bat Cynopterus sphinx exhibits resource defence polygyny and one sexually active male often roosts with groups of females in tents made from leaves. Female bats often lick their mate’s penis during dorsoventral copulation. The female lowers her head to lick the shaft or the base of the male’s penis but does not lick the glans penis which has already penetrated the vagina. Males never withdrew their penis when it was licked by the mating partner. A positive relationship exists between the length of time that the female licked the male’s penis during copulation and the duration of copulation. Furthermore, mating pairs spent significantly more time in copulation if the female licked her mate’s penis than if fellatio was absent. Males also show postcopulatory genital grooming after intromission. At present, we do not know why genital licking occurs, and we present four non-mutually exclusive hypotheses that may explain the function of fellatio in C. sphinx.

http://sciencenow.sciencemag.org/cgi/content/full/2009/1030/2 :

“Zhang and colleagues have a few theories as to why the females would want to increase the length of intercourse. One idea is that it may facilitate sperm transport. Or it could keep males occupied—and thus away from rival females.

Fellatio may also offer protection against sexually transmitted diseases, based on the antimicrobial properties of saliva. Many male animals, including short-nosed fruit bats, lick their genitals after copulation, and in some species this has been shown to reduce the incidence of such diseases.

“The finding of fellatio in bats is exciting news,” says Frans de Waal, a primatologist at Emory University in Atlanta who has worked extensively with bonobos. He says that although the behavior is likely rare, it may be more common than we think. “Part of the reason fellatio is rarely mentioned is shyness about this issue.” The observation provides a unique opportunity to test some theories about the evolutionary role of fellatio, adds Paul Vasey, a behavioral scientist at the University of Lethbridge in Alberta, Canada. Although it’s possible, he says, that bats are just being sexually playful, like their human and bonobo counterparts.”