Detecting Light Flashcards
Describe how bacteriorhodopsin works in archaea.
Bacteriorhodopsin are transmembrane proteins with a prosthetic group called retinal. Retinal absorbs energy from photons which is used to pump protons/hydrogen ions across the bacteriorhodopsin membrane, creating a proton gradient. The protons then diffuse back through the membrane through ATP synthase which generates ATP from ADP and phosphate which creates energy for the cell to use.
Describe how energy is created in plants through photosynthetic pigments in the chloroplasts.
Energy is absorbed by photosynthetic pigments in the chloroplast. This absorbed energy drives a flow of electrons along an electron transport chain and this electron flow is used to pump protons/hydrogen ions across the thyiakoid membrane into the stroma (aqueous fluid). The protons then diffuse back through the membrane through ATP synthase to generate ATP for the plant to use.
What are the two types of photoreceptors in the retina of the eye and what do they do?
Rod cells - Contain only one type of light-sensitive pigment and are sensitive to changes in light intesity.
Cone cells - Not as sensitive to light but are particularly sensitive to specific wavelengths of light (green, red, blue). Allows colour vision.
What is retinal and what does it do in humans?
Retinal is a light-sensitive molecule that captures light in rod and cone cells. It is a prosthetic group bound to opsin and this complex is found in the membranes of photoreceptor cells. Rod cells contain rhodopsin and cone cells contain photopsin.
Describe what happens in humans when a rhodopsin molecule in a rod cell is stimulated by photons.
When stimulated by photons, rhodopsin molecules become excited and this activates the G-proteins they are attached to. This then leads to activation of many enzyme molecules which causes ion channels to close by removing the ligand (cGMP) holding it open. This stops the inward movement of positive ions (calcium and sodium) and so the membrane potential increases. Hyperpolarisation is reached which stimulates a nerve impulse.
Describe how an impulse is generated in cone cells.
Each cone cell has one of three types of photopsin (red, green, blue) which has a maximal sensitivity to a specific wavelength of light. Different photopsins are made by combining retinal with different forms of opsin.
