1 DNA is a polymer. 2  Individual monomer units are called nucleotides. 3  The DNA polymer is composed of: 4  a backbone of molecules of the sugar deoxyribose (a 5 carbon sugar). 5  phosphate groups linking the deoxyribose sugar molecules together in a chain. The DNA polymer is composed of: 2  a backbone of molecules of the sugar deoxyribose (a 5 carbon sugar). 3  phosphate groups linking the deoxyribose sugar molecules together in a chain. 4  four principal bases (2 are pyrimidines and 2 are purines):
Rods and cones function as photoreceptors in the retina of the eye, turning visible light into neuronal signals, which are sent to the brain. This process is called transduction. Rods and cones perform at different wavelengths and sensitivities allowing detailed perception of light and color.
rods and cones. The photoreceptor cells of the retina. They are between the pigment epithelium and the bipolar layer of neurons. The rods contain rhodopsin, which is stimulated by light; the cones contain one of three other photopigments, which are stimulated by various wavelengths of visible light (colors).