The ribosomes function to synthesize polypeptides, the first step in the production of proteins. The polypeptides are excreted into the ER, which modifies them and carries them to the next organelle in the pathway. Because the surface of the smooth ER does not have any ribosomes, it appears smooth under the microscope. The membrane of the smooth ER is the site of lipid and carbohydrate synthesis. The smooth ER also plays a role in detoxifying substances that are harmful to the cell, including some drugs and alcohol. If you examine the liver cells of a person who abuses alcohol, you will find that they contain more smooth ER than the cells of someone who does not abuse alcohol. That is because the smooth ER proliferates in response to the increased need for detoxification.