Motion and locomotion of cells and organisms depends on contractile proteins. The catalysis of all biochemical reactions is done by enzymes , which contain protein. The structure of cells, and the extracellular matrix in which they are embedded, is largely made of protein. The transport of materials in body fluids depends of proteins. The receptors for hormones and other signalling molecules are proteins.
Proteins are an essential nutrient for heterotrophs .
The transcription factors that turn genes on and off to guide the differentiation of the cell and its later responsiveness to signals reaching it are proteins. The protein represented here displays many of the features of proteins. Let's examine some of them as you scroll down the image. Because it is anchored in the plasma membrane of the cell, the heavy chain is called an integral membrane protein . To the right is the protein molecule called beta-2 microglobulin .