7.2 Proteins in the cell and on its surface receive signals from other cells. â¢ There are usually several amplifying steps betweenthe binding of a signal molecule to a cell surfacereceptor and the response of the cell.ecause these proteins may constituteless than 0.01% of the total mass of protein in a cell, puri-fying them is analogous to searching for a particular grainof sand in a sand dune! However, two recent techniqueshave enabled cell biologists to make rapid progress in thisarea. 7.1 Cells signal one another with chemicals.
A macromolecule is a very large molecule commonly created by polymerization of smaller subunits (monomers). They are typically composed of thousands or more atoms.
Macromolecules (also known as supermolecules) are commonly grouped into four major categories: proteins, nucleic acids, lipids and carbohydrates. These are mainly composed of polymers, long molecules made up of a large number of small, similar molecules, or monomers. Proteins are polymers of amino acids. Long amino acid chains are folded into complex shapes, the shape of each determining the function of the protein.