01:146:245 Lecture Notes - Lecture 2: Transducin, Opsin, Rhodopsin

• School: Rutgers University
• Department: Cell Biology and Neuroscience
• Course: 01:146:245
• Professor: Professor Wilhelms

Document Summary

~photoreceptors and bipolar cells have graded potentials, not action potentials. ~graded potentials means the rate of nt released is increased/reduced, not an all- or-none event. ~a photopigment is made of retinal (lipid) + some kind of opsin. ~opsins are specialized for certain wavelengths of light. ~retinal absorbs a photon, which causes activation of transducin (intracellular messenger), which activates enzymes that hydrolyze cgmp (turn it into gmp) ~in the dark, photoreceptors are depolarized to -40 mv. A lot of cyclic gmp in outer segment, keeps na+ and ca2+ channels open. Movement of na+ to inside the cell is called dark current. G-protein is activated, which activates enzymes that decrease amount of cgmp (2nd messenger) Less cyclic gmp (bc converted to gmp), keeps na+ and ca2+ channels closed. Fewer ca2+ channels open means less nt released. ~there is a lot of signal amplification in this cascade. ~light rays bend as they refract, and go slower in denser mediums (cornea and humor)