The chemoattractant and chemorepellent can be defined as any organic or inorganic substance that possess the properties that lead to the inducement of chemotaxis in certain motile cells. These are chemotactic ligands that tend to create a particular chemical concentration of molecular gradients that the organisms, both eukaryotic and prokaryotic, tend to move towards or away from respectively. The effects seen by the chemoattractants can actually be properly elicited via the different chemoreceptors like the methyl-accepting chemotaxis proteins or MCP. The MCPs that are present in the E. coli bacteria include Tsr, Tar, Tap, and Trg. The chemorepellents as well as the chemoattractants tend to bind these MCPs at the extracellular domain.