[Guderian93]

I was browsing tv channels and I came upon a ridiculous history channel alien show, but they were actually talking about an interesting subject; panspermia. I take anything those shows say with a grain of salt but I can't seem to find any actual studies or mention of this.
The show said that Francis Crick, co-discoverer of the DNA, believed that life on Earth was designed by some higher power (aliens) because almost all strands of DNA rotate in only one direction (about the lengthwise axis of the strand) and thus they were engineered. Is this even true?

[Corribus]

No.

http://en.wikipedia.org/wiki/Z-DNA

(Well, it's not true that all DNA rotates in the same direction. Whether or not Crick believed in aliens, I have no idea. But we know a lot more about DNA now than Crick did then, so...)

[Arkcon]

Briefly, the alpha helix (http://en.wikipedia.org/wiki/Alpha_helix) is a common motif in proteins as well as in DNA.  Part of the chirality of important molecules feeds into this -- the (L) form of amino acids is necessary for alpha coils to form, which are in turn very important for biological structures.  So the "design" aspect isn't so important, but its not all a lucky coincidence:  the complexity we see is ironically caused by a certain selectivity of basic building blocks.

[Guderian93]

Yeah I knew from the minute I heard it that most DNA probably rotates a certain direction, but there's definitely a chemical and evolutionary reason for this being common.  They will use any bit of information that could possibly support them and then either distort it or exaggerate its meaning on those shows...it drives me crazy.

[Borek]

there's definitely a chemical and evolutionary reason for this being common

As Arkcon stated, the way large molecules rotate is - at least to some extent - caused by the shape of the building blocks. It happens that all these building blocks are homochiral.

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

[Yggdrasil]

Briefly, the alpha helix (http://en.wikipedia.org/wiki/Alpha_helix) is a common motif in proteins as well as in DNA.

While double-stranded DNA is helical in structure, it is incorrect to say that DNA forms alpha helices.  This term refers only to a specific helical structure formed by polypeptide chains (there are also other helical structures that polypeptides can adopt such as 3₁₀ helices, π helices, and polyproline helices).