Picture yourself inside an ordinary cell in your body. I say ordinary, obviously all cells are special, but some do rather more specialist jobs, like neurons or macrophages. Anyway, find a quiet spot in the cytoplasm of the cell and slowly do a 360 degree turn to take in all the complex structures around you. Do you see them? The Golgi apparatus, the endoplasmic reticulum, the nuclear membrane? What do they all have in common - proteins!
Yes, cells are made of proteins, a few lipids, and quite a bit of nucleic acid. But proteins are everywhere. See the receptors on the cell surface, see the transport proteins moving into the nucleus, see the protein complexes called ribosomes on DNA, transcribing the genetic material. Once the code has been transcribed, proteins are built up from amino acids, each amino acid being translated from three bases of nuclear material.
And these proteins (imagine egg white!) do all sorts of jobs around the cell. For example, enzymes are proteins too. When you bite into a sandwich amylase is released into the saliva from cells in your mouth. An enzyme known as amylase breaks down the starch in the sandwich making it easier for digestion. Useful, don't you think?
The clever thing is that all these proteins, hormones, enzymes, chemical messengers and receptors exist in happy chaos in the milieu of the cell. They all 'know' their place and function and at the right time are ready to exert their actions. They become 'unmixed' and gloriously useful. Yeah for proteins.