DNA is notoriously stable. I’m not sure exactly, I’ve never tested it, but I’d say from personal experience that its good for at least several days, if not weeks (or, quite seriously, years. There’s a reason it came to hold our genetic information). It’s really not something to worry about.

Seeing as how body temperature is warmer than room temperature and it’s stable then, I don’t think you really don’t need to worry about DNA denaturing due to temperature. Or were you worried about degradation?

See, this is what confused me. I would have thought DNA would be okay to be left out in the lab, then again this is bacterial DNA, not human DNA. All my other friends said it’d denature over night. But you know, at work and in college it was always important to keep things in the freezer and I kept wondering but felt stupid to ask why.

Well, comparison to body temperature isn’t quite fair, since DNA in a living system has tons of proteins around it to make sure it stays well behaved. But still, DNA is quite stable. Bacterial DNA is no less stable then human (or any other) DNA, it’s the exact same molecule, just in a different order. Most is, to a degree, more stable, since it’s in plasmids (small circular DNA) instead of the linear chromosomal DNA we have. The length of the strands can change things, so small segments of a dozen bases or so won’t be as stable, but DNA stability actually maxes out around 20–30 bases, after that it’s already so stable you can’t really measure the stability differences anymore.

Also, I’ve left DNA, even shorter DNA, out overnight several times, it’s not an issue. Usually we keep stuff in freezers just to be safe (and to make sure it’s good for a very long time, should it be needed), but it’s not very necessary, especially over the short term.

Thousands of years. This article might give you an idea:

http://en.wikipedia.org/wiki/Neanderthal_genome_project

“The researchers recovered ancient DNA of Neanderthals by extracting the DNA from the femur bones of three 38,000-year-old female Neanderthal specimens from Vindija Cave, Croatia, and other bones found in Spain, Russia, and Germany. Only about half a gram of the bone samples was required for the sequencing, but the project faced many difficulties, including the contamination of the samples by the bacteria that had colonized the Neanderthal’s body and humans who handled the bones at the excavation site and at the laboratory.”

These answers are all true, DNA itself is very, very stable at a wide range of temperatures, however if your tube is dirty, or if your sample isn’t purified, you can run in to issues with nucleases chewing it up. It isn’t denaturation, it is actually cleavage/degradation of the strand itself. Just make sure you wear your gloves when you’re dealing with it, avoid areas of the lab where people are isolating RNA (usually use DNAse, which will destroy your stuff), and use a good purification protocol and you should be good.