phase-contrast microscope   Type of light microscope that exploits the interference effects that occur when light passes through material of different refractive indices. Used to view living cells. (Figure 9–7) phenotype The observable character (including both physical appearance and behavior) of a cell or organism. (Panel 8–2, p. 486) phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2, PIP2] Membrane inositol phospholipid (a phosphoinositide) that is cleaved by phospholipase C into IP3 and diacylglycerol at the beginning of the inositol phospholipid signaling pathway. It can also be phosphorylated by PI 3-kinase to produce PIP3 docking sites for signaling proteins in the PI-3-kinase–Akt signaling pathway. (Figures 15–28 and 15–53) phosphoglyceride   Phospholipid derived from glycerol, abundant in biomembranes. (Figures 10–2 and 10–3) phosphoinositide A lipid containing a phosphorylated inositol derivative. Minor component of the plasma membrane, but important in demarking different membranes and for intracellular signal transduction in eukaryotic cells. (Figure 15–52) phosphoinositide 3-kinase (PI 3-kinase) Membrane-bound enzyme that is a component of the PI-3-kinase–Akt intracellular signaling pathway. It phosphorylates phosphatidylinositol 4,5-bisphosphate at the 3 position on the inositol ring to produce PIP3 docking sites in the membrane for other intracellular signaling proteins. (Figure 15–53) phosphoinositides (PIPs; phosphatidylinositol phosphates) A lipid containing a phosphorylated inositol derivative. Minor component of the plasma membrane, but important in demarking different membranes and for intracellular signal transduction in eukaryotic cells. (Figure 13–10) phospholipase C (PLC) Membrane-bound enzyme that cleaves inositol phospholipids to produce IP3 and diacylglycerol in the inositol phospholipid signaling pathway. PLCβ is activated by GPCRs via specific G proteins, while PLCγ is activated by RTKs. (Figure 15–55) phospholipid The main category of lipids used to construct biomembranes. Generally composed of two fatty acids linked through glycerol (or sphingosine) phosphate to one of a variety of polar groups. (FIgure 10–3, and Panel 2–5, pp. 98–99) phosphorylation   Reaction in which a phosphate group is covalently coupled to another molecule.
photoactivation   Technique for studying intracellular processes in which an inactive form of a molecule of interest is introduced into the cell, and is then activated by a focused beam of light at a precise spot in the cell. (Figure 9–28) photochemical reaction center The part of a photosystem that converts light energy into chemical energy in photosynthesis. (Figure 14–44) photosynthetic electron-transfer reactions Light-driven reactions in photosynthesis in which electrons move along an electron-transport chain in a membrane, generating ATP and NADPH.
photosystem   Multiprotein complex involved in photosynthesis that captures the energy of sunlight and converts it to useful forms of energy: a reaction center plus an antenna (Figure 14–45) phototropin   Photoprotein associated with the plant plasma membrane that senses blue light and is partly responsible for phototropism.