The endoplasmic reticulum (ER), is a network of tubes and vesicles, or transporting molecules, inside an animal cell next to the nucleus. The main functions of the endoplasmic reticulum include synthesizing protein molecules; synthesizing lipids and fats, like cholesterol; and the metabolism of drugs and medicines. Since there are two different types of endoplsmic reticulum — rough and smooth ER — each type focuses on different functions. The functions of the endoplasmic reticulum also include the transport of protein molecules, which are moved along the cytoskeleton toward their appropriate place inside the cell, through tiny transporting systems called vesicles.
The rough endoplasmic reticulum is commonly associated with the function of synthesizing proteins and transporting protein molecules to different parts of the cell. The membrane of the rough ER is studded with ribosomes, which are components that produce proteins from their building blocks, amino acids. Once the protein is synthesized through the rough ER, it is then secreted out of the nuclear envelope of the organelle and into the vesicles. These vesicles are small compartments that move the protein molecules down the cytoskeleton of the cell, which is composed of cytoplasm and acts to move molecules through the cell to their desired destination.
Connected to the nuclear envelope of the cell, the smooth endoplasmic reticulum synthesizes steroid hormones, like cholesterol, among other things. Other functions of the smooth endoplasmic reticulum include the making of lipids, or fats, which is important for the stability of the cell membrane. The smooth ER also helps metabolize carbohydrates, a macronutrient present in foods and used as an energy source for the body. The smooth endoplasmic reticulum can be distinguished from the rough by its smooth texture and the absence of studded ribosomes.
The endoplasmic reticulum also functions to metabolize drugs and medicines by modifying certain enzymes. The ER is important for detoxifying the body of certain compounds, and this is where the endoplasmic reticulum in liver cells comes into play. The functions of the endoplasmic reticulum are not only important because they help break down certain compounds, but because they help produce protein and fats that are important for the stability of cell membranes and the communication between cells. These components also act as energy sources for the body as well as facilitating metabolic changes inside the cell.