Question

How would the structure of a fish's DNA compare with the structure of a lion's DNA?

Answer 1

The double helix is pretty ubiquitous in DNA. Lions have AGTC - so do we, so do fish. With AGTC, the double helix is the most stable arrangement for keeping the genome intact. The gene structures (which is to say, sequence), differ, as do promoters and such - but the structure of the DNA is the same.