U1 - The Eye Flashcards
What is the retina?
The retina is the area within the eye that detects light
What are the two types of photoreceptor cells?
Rod cells and cone cells
What are Rods?
Rods function in dim light but do not allow colour preception
What are cones?
Cone cells are responsible for colour vision and only function in bright light.
What combination forms Photoreceptors in the eye?
The light-sensitive molecule Retinal and the memebrane protein Opsin.
The Retinal opsin complex is called Rhodopsin.
What happens when a retinal absorbs a photon of light
Rhodopsin changes conformation to photoexcited rhodopsin. A cascade of proteins then amplifies the signal.
What type of protein does photo excited Rhodopsin activate?
It activates a G-Protein called TRANSDUCIN, which activates the enzyme Phosphodiestrerase (PDE)
What can a single photoexcited molecule activate?
It can activate hundreds of molecules of G-Proteins and each activated G-Protein activates one molecule of PDE.
What does PDE do?
PDE catalyses the hydrolysis of a molecule called cyclin GMP (cGMP)
Whats does Active PDE do?
Each acive PDE molecule breaks down thousands of cGMP molecules per second.
What happens because of the reduction of cGMP?
The reduction on cGMP concentration as a result of it hydrolysis affects the function of ion channels in the membrane of rod cells.
What effect does the reduction of cGMP have on the effect of ion channels?
This results in the closure of ion channels in the membrane of rod cells, which triggers the nerve impluses on neurons in the retina.
What does a high degree of amplification result in for rod cells?
Results in rod cells being able to respond to low intensities of light
In cone cells, there is a different form on retinal. Each have a maximal sensitivity to what?
Specific wavelengths: red, blue, green or UV
