This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Transducin is a protein found in 
Select and explain. 
A. Glomerulus, B. Retina, C. Skeletal muscle, D. Adrenal medulla
B: Retina
Answer: B: Retina 
Explanation: Transducin (Gt) is a protein naturally expressed in veebrate retina rods and cones and it is very impoant in veebrate phototransduction. It is a type of heterotrimeric G-protein with different a subunits in rod and cone photoreceptors. Light leads to conformational changes in rhodopsin, which in turn leads to the activation of transducin. Transducin activates phosphodiesterase, which results in the breakdown of cGMP. The intensity of the flash response is directly propoional to the number of transducin activated. Ref: guyton and hall textbook of medical physiology 12 edition page number: 742,743,744