Gram-positive bacteria have a cell wall that is made primarily of peptidoglycan. In the peptidoglycan cell wall, there are acidic molecules called teichoic acids. The teichoic acids are partially responsible for the negative charge of the gram-positive bacteria cell and the transport of Ca2+ and Mg2+. Some teichoic acids are covelentley bound to membrane lipids and they are called lipoteichoic acids. Due to the majority peptidoglycan cell wall, gram positive bacteria retain the violet dye of the test.