They are characterized by highly conserved ATP binding domains. The first ABC transporter discovered was the product of the multidrug resistance gene that makes cancer cells resistant to a variety of drugs used in chemotherapy. They occur in lysosomes, secretory granules and plant cell vacuole membranes . The absorption of light energy by the retinal group induces a series of conformational changes in the protein that cause a proton to move from the retinal group, through a channel in the protein, to the cell exterior. The proton donated by the photo-exited retinal is replaced by another proton transferred to the proteins from the cytoplasm.
Electron transfer can provide energy.
Oxydation reduction reactions involve the transfer of electrons from one substance to another with release of free energy, a mechanism by which cells capture energy from food and sunlight. These reactions occur in PM, Mit . Coupling Active Transport to Existing Ion Gradients . Phagocytosis occurs when the material contained within the vesicles consists mainly of particulate matter. Phagocytosis permits the uptake and degradation of particles whose sizes approach that of the cell itself.