The integumentary system (skin) has been called a membrane and an organ but, it is generally considered a system because it has organs that work together as a system. It is sometimes considered an organ because it contains several types of tissues and a membrane and it covers the body.
Structurally, DNA and RNA are nearly identical. As mentioned earlier, however, there are three fundamental differences that account for the very different functions of the two molecules. RNA has a ribose sugar instead of a deoxyribose sugar like DNA. RNA nucleotides have a uracil base instead of thymine.
