text: Proteins have many different functions in a cell and the function may vary based on the polypeptides they interact with and their cellular environment. Chaperone proteins work to stabilize newly synthesized proteins. They ensure the new protein folds into its correct functional conformation in addition to making sure products do not aggregate in areas where they should not. Proteins can also function as enzymes, increasing the rate of various biochemical reactions and turning substrates into products. Products can be modified by attaching groups such as phosphate via an enzyme to specific amino acids in the primary sequence. Proteins can also be used to move molecules in the cell to where they are needed, these are called motor proteins. The shape of the cell is supported by proteins. Proteins such as actin, microtubules and intermediate filaments provide structure to the cell. Another class of proteins are found in plasma membranes. Membrane proteins can be associated with the plasma membrane in different ways, depending on their structure. These proteins allow the cell to import or export cell products, nutrients or signals to and from the extracellular space. Other proteins help the cell to perform regulatory functions. For example, transcription factors bind to DNA to help transcription of RNA.