Re: cDNA
Text to speech already exists, so prior art would invalidate your speaking machine patent. Similarly, speech to text also already exists so ditto on that.
Reading a work aloud is considered a "performance" of the work. A recording of said performance could be copyrighted separately from the original work, even if the original work is in the Public Domain. (This is how Disney owns the copyright on a number of works that are derived entirely from Public Domain fairy tales.) Should the original source material NOT be Public Domain then unless you obtained the performance rights, your derived work would violate copyright.
A better analogy might be carving a baseball bat out of a log. Nature made the tree branch the log came from, but you made the baseball bat by carving away the wood you didn't want. Arguably a baseball bat would be patentable if you were the first to come up with the idea.
It's also important to note that cDNA is merely patent *eligible* which means (in theory) that it still needs to be novel and useful before a patent is awarded. (I know, I know, US Patent office, etc... You can all stop sniggering now.)