Structural biology is a branch of biology, biochemistry, and biophysics involved in the nature of macromolecules of living organisms (mainly proteins, which are made up of amino acids, RNA or DNA, made of nucleotides, membranes, made of lipids) how they get the composition they have, and how their conversion affects their performance. This subject is of great interest to biologists because macromolecules perform many functions of cells, and it is only by combining them into complex three-dimensional structures that they are able to perform these functions. This construction, the "tertiary structure" of molecules, moves in a complex way to the basic structure of each molecule, or "elemental structure." Hemoglobin, the oxygen-transporting protein found in the red blood cells of the Biomolecule, is too small to see in detail even with light microscopes. The methods scientists use to determine gene structures often include measuring the number of identical molecules at a time.