cAMP has several different functions. It acts as a key regulator of cellular function in a wide range of organisms including humans, plants, and amoebas. Processes such as memory, gene regulation, immune function, and metabolism are all regulated by cAMP.  cAMP plays a key role as a second messenger for signal transduction at the molecular level. Specifically, it conveys the cAMP-dependent pathway and is used in transferring glucagon and adrenaline into cells. These hormones are unable to pass through the plasma membrane of target cells and need cAMP as a second messenger to do so. cAMP also functions by binding to the regulatory subunits of protein kinase A and activating it. Activated PKA may phosphorylate specific proteins bound to the promoter regions of DNA and thus enhance transcription. cAMP also has a role in the regulation of the passage of calcium ions through ion channels. Its activation of calcium channels allows for the formation of a minor pathway which modulates the release of growth hormones. In bacteria, cAMP is involved in the regulation of bacterial lac operon in relation with the culture medium used for bacterial growth.