very interesting question. it all has to do with DNA, which is a long strand of molecules. basically, only certain parts of the DNA, called genes, are used to in every cells. for instance, a bone cell will only use genes that allow it to build or break down bone
Proteins and phospholipids make up most of the membrane structure. The phospholipids make the basic bag, while the proteins are found around the holes and help move molecules in and out of the cell.
