Strictly speaking, what is the definition of cDNA? This confuses me, since usually it is said to refer to DNA that is complementary to mRNA. Is this correct? Is it restricted to mature mRNA?
I also find directionality very confusing. As I understand it, mRNA has a sequence equivalent (less introns, after splicing) to the so-called 'coding strand' of DNA. Does this mean that cDNA made from mRNA, at least before treated with a DNA polymerase, is also complementary to the original genomic DNA? Is this the better definition (I have seen this used as well, though the first definition seems far more common).
Lastly, as I understand it each chromosome has a forward and reverse strand, defined by convention, but that the 'coding' strand of a given gene is random. This seems counter-intuitive... is it just because both strands are equivalent? Does it introduce complications in terms of the cell 'knowing' which strand is the coding strand for a gene?
The most upvoted reply to this question (http://www.biostars.org/p/3423/) confused me even further. I feel the same way as 'Onefishtwofish' does, in the replies. Can anyone clarify?