DNA, proteins, and eating

A few weeks back, we were watching a PBS show, probably Nova, about the Human Genome Project. It was stated that most people are very surprised to learn how much DNA humans share with the rest of the animals–I don’t remember the exact numbers, but it was about 99% for chimpanzees and 95% for mice. I do not find this information at all surprising myself, but it popped into my head at that moment that it would have to be that way, because if we didn’t have similar DNA, we wouldn’t make the same proteins or amino acids, and we wouldn’t be able to eat each other.

However, I’m not really all that knowledgeable about biology and DNA, so I put it to the Dopers: am I right in thinking that animals with different DNA might make different proteins and whatnot, and would thus be indigestible to humans (or tigers for that matter)? If so, why? And why don’t they ever mention that on Nova when talking about how much DNA we share with other species? I’ve read some books on these topics, and nothing has ever been said about it (maybe that just means I’m wrong).

And, if we went to other planets with different lifeforms made of different stuff, would they be poisonous or inedible?

All life as we know it makes its proteins mostly from the same set of twenty amino acids (some other amino acids do wind up in certain proteins, but they are minor components and are not required nutrients). Yet, contrary to what your supposition would require, DNA identity is not so high among all organisms. The plants that we eat, for example, have DNA that is way below 90% identical to ours.