Five parallel intracellular signaling pathways activated by G-protein-linked receptors, receptor tyrosine kinases, or both In this schematic example, the five kinases (shaded yellow) at the end of each pathway phosphorylate target proteins (shaded red), some of which are phosphorylated by more than one of the kinases. The specific phospholipase C activated by the two types of receptors is different: G-protein-linked receptors activate PLC-β, whereas receptor tyrosine kinases activate PLC-γ (not shown). Molecular switches active- inactive form
Figure 15-79. When activated by light, the phytochrome, which is a dimer, phosphorylates itself and then moves into the nucleus, where it activates gene regulatory proteins to stimulate the transcription of specific genes. (Alberts et al., 2002)
Figure 1. Photomorphogenesis as a morphological and as a cellular process. The left photos show the change in form of an Arabidopsis thaliana seedling grown in darkness (top) or in white light. The right hand illustration shows the change in chloroplast structure and diagrams the progress of light signals through two receptor systems, cryptochrome and phytochrome. Adapted from Biochemistry and Molecular Biology of Plants, (c) American Society of Plant Biologists, with permission.