Golgi apparatus (Golgi complex) Complex organelle in eukaryotic cells, centered on a stack of flattened, membrane-enclosed spaces, in which proteins and lipids transferred from the endoplasmic reticulum are modified and sorted. It is the site of synthesis of many cell wall polysaccharides in plants and extracellular matrix glycosaminoglycans in animal cells. (Figure 13–26)
GPCR kinase (GRK) Member of a family of enzymes that phosphorylates multiple serines and threonines on a GPCR to produce receptor desensitization. (Figure 15–42)
G protein (trimeric GTP-binding protein) A trimeric GTP-binding protein with intrinsic GTPase activity that couples GPCRs to enzymes or ion channels in the plasma membrane. (Table 15–3, p. 846)
G-protein-coupled receptor (GPCR) A seven-pass cell-surface receptor that, when activated by its extracellular ligand, activates a G protein, which in turn activates either an enzyme or ion channel in the plasma membrane. (Figures 15–6 and 15–21)
Gq   Class of G protein that couples GPCRs to phospholipase C-β to activate the inositol phospholipid signaling pathway.
Gram negative Description for bacteria that do not stain with Gram stain as a result of having a thinner peptidoglycan cell wall outside their inner (plasma) membrane, and on an additional outer membrane.
Gram positive Description for bacteria that stain positive with Gram stain due to a thick layer of peptidoglycan cell wall outside their inner (plasma) membrane.
Gram staining A technique for classifying bacteria based on differences in the structure of the bacterial cell wall and outer surface.
granulocyte Category of white blood cell distinguished by conspicuous cytoplasmic granules. Includes neutrophils, basophils, and eosinophils. Arises from a granulocyte/ macrophage (GM) progenitor cell. (Figure 22–27) granulocyte/macrophage (GM) progenitor cell Committed progenitor cell in the bone marrow that gives rise to neutrophils and macrophages. (Figure 22–31) green fluorescent protein (GFP) Fluorescent protein isolated from a jellyfish. Widely used as a marker in cell biology. (Figure 9–24) growth cone   Migrating motile tip of a growing nerve cell axon or dendrite. (Figure 21–72) growth factor   Extracellular signal protein that can stimulate a cell to grow. They often have other functions as well, including stimulating cells to survive or proliferate. Examples include epidermal growth factor (EGF) and platelet-derived growth factor (PDGF).
growth hormone (GH) Mammalian hormone secreted by the pituitary gland into the bloodstream that stimulates growth throughout the body.
GTP (guanosine 5′-triphosphate) Nucleoside triphosphate produced by the phosphorylation of GDP (guanosine diphosphate). Like ATP, it releases a large amount of free energy on hydrolysis of its terminal phosphate group. Has a special role in microtubule assembly, protein synthesis, and cell signaling. (Figure 2–58)
GTP-binding protein Also called GTPase; an enzyme that converts GTP to GDP.