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Flashcards in Kapitel 15 Deck (116)

Adjustment of sensitivity following repeated stimulation. The mechanism that allows a cell to react to small changes in stimuli even against a high background level of stimulation.

adaptation (desensitization)


General term for a protein that functions solely to link two or more different proteins together in an intracellular signaling pathway or protein complex. (Figure 15–11)

adaptor protein - adaptor


Membrane-bound enzyme that catalyzes the formation of cyclic AMP from ATP. An important component of some intracellular signaling pathways.

adenylyl cyclase (adenylate cyclase)


Serine/threonine protein kinase that acts in the PI-3-kinase/Akt intracellular signaling pathway involved especially in signaling cells to grow and survive. Also called protein kinase B (PKB).



Member of a family of proteins that contributes to GPCR desensitization by preventing the activated receptor from interacting with G proteins and serving as an adaptor to couple the receptor to clathrin-dependent endocytosis. (Figure 15–42)



Plant hormone - commonly indole-3-acetic acid - with numerous roles in plant growth and development.



Multifunctional cytoplasmic protein involved in cadherin-mediated cell–cell adhesion - linking cadherins to the actin cytoskeleton. Can also act independently as a transcription regulatory protein. Has an important role in animal development as part of a Wnt signaling pathway.

beta-catenin (β-catenin)


Class of steroid signal molecules in plants that regulate the growth and differentiation of plants throughout their life cycle via binding to a cell-surface receptor kinase to initiate a signaling cascade.



Serine/threonine protein kinase that is activated by Ca2+/calmodulin. Indirectly mediates the effects of an increase in cytosolic Ca2+ by phosphorylating specific target proteins. (Figure 15–33)

Ca2+/calmodulin-dependent kinase (CaM-kinase)


Ubiquitous intracellular Ca2+-binding protein that undergoes a large conformation change when it binds Ca2+ - allowing it to regulate the activity of many target proteins. In its activated (Ca2+-bound) form - it is called Ca2+/calmodulin. (Figure 15–33)



Multifunctional Ca2+/calmodulin-dependent protein kinase that phosphorylates itself and various target proteins when activated. Found in most animal cells but is especially abundant at synapses in the brain - and is involved in some forms of synaptic plasticity in vertebrates. (Figure 15–34)

CaM-kinase II


Member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons - cell-cycle progression - gene transcription - and membrane transport.



Internal cyclical process that produces a particular change in a cell or organism with a period of around 24 hours - for example the sleep-wakefulness cycle in humans.

circadian clock


Photoreceptor cell in the vertebrate retina that is responsible for color vision in bright light.

cone photoreceptor (cone)


Form of intercellular signaling in which signal molecules remain bound to the surface of the signaling cell and influence only cells that contact it.

contact-dependent signaling


Transcription regulator that recognizes the cyclic AMP response element (CRE) in the regulatory region of genes activated by cAMP. On activation by PKA - phosphorylated CREB recruits a transcriptional coactivator (CREB-binding protein; CBP) to stimulate transcription of target genes.

CRE-binding (CREB) protein


Plant flavoprotein sensitive to blue light. Structurally related to blue-light-sensitive enzymes called photolyases (involved in the repair of ultraviolet-induced DNA damage) but do not have a role in DNA repair. Also found in animals - where they have an important role in circadian clocks.



Latent transcription regulator that mediates the effects of Hedgehog.

Cubitus interruptus (Ci)


Nucleotide that is generated from ATP by adenylyl cyclase in response to various extracellular signals. It acts as a small intracellular signaling molecule - mainly by activating cAMP-dependent protein kinase (PKA). It is hydrolyzed to AMP by a phosphodiesterase. (Figure 15–25)

cyclic AMP (cAMP)


Specific enzyme that rapidly and continuously destroys cyclic AMP - forming 5′-AMP. (Figure 15–25).

cyclic AMP phosphodiesterase


Enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP. (Figure 15–26)

cyclic AMP-dependent protein kinase (protein kinase A - PKA)


Nucleotide that is generated from GTP by guanylyl cyclase in response to various extracellular signals.

cyclic GMP (cGMP)


Specific enzyme that rapidly hydrolyzes and degrades cyclic GMP.

cyclic GMP phosphodiesterase


Cell-surface receptor that binds a specific cytokine or hormone and acts through the JAK–STAT signaling pathway. (Figure 15–56)

cytokine receptor


Enzyme activated by certain cell-surface receptors (tyrosine-kinase-associated receptors) that transmits the receptor signal onward by phosphorylating target cytoplasmic proteins on tyrosine side chains.

cytoplasmic tyrosine kinase


Single-pass transmembrane signal protein displayed on the surface of cells that binds to the Notch receptor protein on a neighboring cell - activating a contact-dependent signaling mechanism.



see adaptation



Lipid produced by the cleavage of inositol phospholipids in response to extracellular signals. Composed of two fatty acid chains linked to glycerol - it serves as a small signaling molecule to help activate protein kinase C (PKC). (Figure 15–28)

diacylglycerol (DAG)


Scaffold protein recruited to the Frizzled family of cell-surface receptors upon their activation by Wnt binding that helps relay the signal to other signaling molecules.



Specialized animal cell that secretes a hormone into the blood. Usually part of a gland - such as the thyroid or pituitary gland.

endocrine cell


A major type of cell-surface receptor that has a cytoplasmic domain that either has enzymatic activity or is associated with an intracellular enzyme. In either case - the enzymatic activity is stimulated by an extracellular ligand binding to the receptor. (Figure 15–6)

enzyme-coupled receptor


One of a family of membrane-bound protein ligands for the Eph receptor tyrosine kinases (RTKs) that - among many other functions - stimulate repulsion or attraction responses that guide the migration of cells and nerve cell axons during animal development.



Small gas molecule that is a plant growth regulator influencing plant development in various way including promoting fruit ripening - leaf abscission - and plant senescence and functioning as a stress signal in response to wounding - infection - and flooding.



Any secreted or cell-surface chemical signal that binds to receptors and regulates the activity of the cell expressing the receptor.

extracellular signal molecule


Cytoplasmic tyrosine kinase present at cell–matrix junctions (focal adhesions) in association with the cytoplasmic tails of integrins.

focal adhesion kinase (FAK)


Family of cell-surface receptors that are seven-pass transmembrane proteins that resemble GPCRs in structure but do not generally work through the activation of G proteins. Activated by Wnt binding to recruit the scaffold protein Dishevelled - which helps relay the signal to other signaling molecules.



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 (trimeric GTP-binding protein)


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)

G-protein-coupled receptor (GPCR)


Member of a family of enzymes that phosphorylates multiple serines and threonines on a GPCR to produce receptor desensitization. (Figure 15–42)

GPCR kinase (GRK)


Class of G protein that couples GPCRs to phospholipase C-β to activate the inositol phospholipid signaling pathway.



Protein that binds to a GTPase and inhibits it by stimulating its GTPase activity - causing the enzyme to hydrolyze its bound GTP to GDP. (Figure 15–8)

GTPase-activating protein (GAP)


Protein that binds to a GTPase and activates it by stimulating it to release its tightly bound GDP - thereby allowing it to bind GTP in its place. (Figure 15–8)

guanine nucleotide exchange factor (GEF)


Secreted extracellular signal molecule that has many different roles controlling cell differentiation and gene expression in animal embryos and adult tissues. Excessive Hedgehog signaling can lead to cancer.

Hedgehog protein


Signal molecule secreted by an endocrine cell into the bloodstream - which can then carry the signal to distant target cells.



Inhibitory proteins that bind tightly to NFκB dimers and hold them in an inactive state within the cytoplasm of unstimulated cells.



Protein with four or five immunoglobulin-like domains and two or three fibronectin-type-III-like domains; located on the cell surface and thought to serve as co-receptors for Hedgehog proteins.



Trimeric G protein that can regulate ion channels and inhibit the enzyme adenylyl cyclase in the plasma membrane. (Table 15–3 - p. 846)

inhibitory G protein (Gi)


Small intracellular signaling molecule produced during activation of the inositol phospholipid signaling pathway. Acts to release Ca2+ from the endoplasmic reticulum. (Figures 15–28 and 15–29)

inositol 1 -4 -5-trisphosphate (IP3)


Intracellular signaling pathway that starts with the activation of phospholipase C and the generation of IP3 and diacylglycerol (DAG) from inositol phospholipids in the plasma membrane. The DAG helps to activate protein kinase C. (Figures 15–28 and 15–29)

inositol phospholipid signaling pathway


Compact protein module - found in many intracellular signaling proteins - that binds to a particular structural motif (e.g. - a short peptide sequence - a covalent modification - or another protein domain) in another protein or lipid.

interaction domain


Ion channel found at chemical synapses in the postsynaptic plasma membranes of nerve and muscle cells. Opens only in response to the binding of a specific extracellular neurotransmitter. The resulting inflow of ions leads to the generation of a local electrical signal in the postsynaptic cell. (Figures 15–6 and 11–35)

ion-channel-coupled receptor (transmitter-gated ion channel - ionotropic receptor)


Gated Ca2+ channel in the ER membrane that opens on binding cytosolic IP3 - releasing stored Ca2+ into the cytosol. (Figure 15–29)

IP3-gated Ca2+-release channel (IP3 receptor)


Signaling pathway activated by cytokines and some hormones - providing a rapid route from the plasma membrane to the nucleus to alter gene transcription. Involves cytoplasmic Janus kinases (JAKs) - and signal transducers and activators of transcription (STATs).

JAK–STAT signaling pathway


Cytoplasmic tyrosine kinases associated with cytokine receptors - which phosphorylate and activate transcription regulators called STATs.

Janus kinases (JAKs)


Intracellular signaling pathway in which one protein kinase - activated by phosphorylation - phosphorylates the next protein kinase in the sequence - and so on - relaying the signal onward.

kinase cascade


Co-receptor bound by Wnt proteins in the regulation of β-catenin proteolysis.

LDL-receptor-related protein (LRP)


Common type of receptor serine/threonine kinase in plants that contains a tandem array of leucine-rich repeat sequences in its extracellular portion.

leucine-rich repeat (LRR) receptor kinases


Extracellular signal molecule that acts on neighboring cells.

local mediator


An intracellular signaling module composed of three protein kinases - acting in sequence - with MAP kinase as the third. Typically activated by a Ras protein in response to extracellular signals. (Figure 15–49)

MAP kinase module (mitogen-activated protein kinase module)


A single-subunit enzyme that converts GTP to GDP (also called small monomeric GTP-binding proteins). Cycles between an active GTP-bound form and an inactive GDP-bound form and frequently acts as a molecular switch in intracellular signaling pathways.

monomeric GTPase


The TOR of mammalian cells - which exists in two functionally distinct multiprotein complexes.



Latent transcription regulator that is activated by various intracellular signaling pathways when cells are stimulated during immune - inflammatory - or stress responses. Also has important roles in animal development. (Figure 15–62)

NFκB protein


Gaseous signal molecule that is widely used in cell–cell communication in both animals and plants. (Figure 15–40)

nitric oxide (NO)


Enzyme that synthesizes nitric oxide (NO) by the deamination of arginine. (Figure 15–40B)

NO synthase (NOS)


Transmembrane receptor protein (and latent transcription regulator) involved in many cell-fate choices in animal development - for example in the specification of nerve cells from ectodermal epithelium. Its ligands are cell-surface proteins such as Delta and Serrate. (Figure 15–59)



Intracellular receptors for hydrophobic signal molecules such as steroid and thyroid hormones and retinoic acid. The receptor-ligand complex acts as a transcription factor in the nucleus. (Figure 15–65)

nuclear receptor superfamily


G-protein-coupled receptors on the modified cilia of olfactory receptor neurons that recognize odors. The receptors activate adenylyl cyclase via an olfactory-specific G protein (Golf) and resultant increases in cAMP open cyclic-AMP-gated cation channels - allowing Na+ influx and depolarization and initiation of a nerve impulse.

olfactory receptors


Short-range cell–cell communication via secreted signal molecules that act on neighboring cells. (Figure 15–2)

paracrine signaling


Transmembrane protein predicted to cross the plasma membrane 12 times; much is in intracellular vesicles and some is on the cell surface where it binds the Hedgehog protein.



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)

phosphatidylinositol 4 -5-bisphosphate [PI(4 -5)P2 - PIP2]


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)



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)

phosphoinositide 3-kinase (PI 3-kinase)


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)

phospholipase C (PLC)


Reaction in which a phosphate group is covalently coupled to another molecule.



Photoprotein associated with the plant plasma membrane that senses blue light and is partly responsible for phototropism.



Plant photoprotein that senses light via a covalently attached light-absorbing chromophore - which changes its shape in response to light and then induces a change in the protein’s conformation. Plant phytochromes are dimeric - cytoplasmic serine/threonine kinases - which respond differentially and reversibly to red and far-red light to alter cell behavior.



Intracellular signaling pathway that stimulates animal cells to survive and grow. (Figure 15–53)

PI-3-kinase–Akt pathway


Signal molecule that helps coordinate growth and development. Examples are ethylene - auxins - gibberellins - cytokinins - abscisic acid - and the brassinosteroids.

plant growth regulator (plant hormone)


Protein domain found in some intracellular signaling proteins. Some PH domains in intracellular signaling proteins bind to phosphatidylinositol 3 -4 -5-trisphosphate produced by PI 3-kinase - bringing the signaling protein to the plasma membrane when PI 3-kinase is activated.

pleckstrin homology domain (PH domain)


Short - single - nonmotile cilium lacking dynein that arises from a centriole and projects from the surface of many animal cell types. Some signaling proteins are concentrated in the primary cilium. (Figure 15–38)

primary cilium


Ca2+-dependent protein kinase that - when activated by diacylglycerol and an increase in the concentration of cytosolic Ca2+ - phosphorylates target proteins on specific serine and threonine residues. (Figure 15–29)

protein kinase C (PKC)


Enzyme that catalyzes phosphate removal from amino acids of a target protein.

protein phosphatase


Enzyme that removes phosphate groups from phosphorylated tyrosine residues on proteins.

protein tyrosine phosphatase


Member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons - cell-cycle progression - gene transcription - and membrane transport.



Monomeric GTPase of the Ras superfamily that helps to relay signals from cell-surface receptor tyrosine kinase receptors to the nucleus - frequently in response to signals that stimulate cell division. Named for the ras gene - first identified in viruses that cause rat sarcomas. (Figure 3–67)

Ras (Ras protein)


Large superfamily of monomeric GTPases (also called small GTP-binding proteins) of which Ras is the prototypical member. (Table 15–5 - p. 854)

Ras superfamily


Ras GTPase-activating proteins; increase the rate of hydrolysis of bound GTP by Ras - thereby inactivating Ras.



Ras guanine nucleotide exchange factors; stimulate the dissociation of GDP and the subsequent uptake of GTP from the cytosol - thereby activating Ras.



Intracellular signaling pathway that relays signals from activated receptor tyrosine kinases to effector proteins in the cell including transcription regulators in the nucleus.

Ras–MAP-kinase signaling pathway


Any protein that binds a specific signal molecule (ligand) and initiates a response in the cell. Some are on the cell surface - while others are inside the cell. (Figure 15–3)



Cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on serine or threonine residues in response to ligand binding. The TGFβ receptor is an example. (Figure 15–57)

receptor serine/threonine kinase


Cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on tyrosine residues in response to ligand binding. (Figure 15–43 and Table 15–4 - p. 850)

receptor tyrosine kinase (RTK)


A GAP protein that binds to a trimeric G protein and enhances its GTPase activity - thus helping to limit G-protein-mediated signaling. (Figure 15–8)

regulator of G protein signaling (RGS)


A monomeric Ras-related GTPase that in its active form (Rheb-GTP) activates mTOR - which promotes cell growth.



Member of the Rho family of monomeric GTPases that regulate the actin and microtubule cytoskeletons - cell-cycle progression - gene transcription - and membrane transport.



Family of monomeric GTPases within the Ras superfamily involved in signaling the rearrangement of the cytoskeleton. Includes Rho - Rac - and Cdc42. (Table 15–5 - p. 854)

Rho family


Seven-span membrane protein of the GPCR family that acts as a light sensor in rod photoreceptor cells in the vertebrate retina. Contains the light-sensitive prosthetic group retinol. (Figure 15–39)



Photoreceptor cell in the vertebrate retina that is responsible for noncolor vision in dim light.

rod photoreceptor (rod)


A regulated Ca2+ channel in the ER membrane that opens in response to rising Ca2+ levels and thus amplifies the Ca2+ signal.

ryanodine receptor


Small intracellular signaling molecule that is formed or released for action in response to an extracellular signal and helps to relay the signal within the cell. Examples include cyclic AMP - cyclic GMP - IP3 - Ca2+ - and diacylglycerol.

second messenger (small intracellular mediator)


Enzyme that phosphorylates specific proteins on serine or threonines.

serine/threonine kinase


Src homology region 2 - a protein domain present in many signaling proteins. Binds a short amino acid sequence containing a phosphotyrosine. (Panel 3–2 - pp. 142–143)

SH2 domain


Latent transcription regulators that are phosphorylated and activated by receptor serine/threonine kinases and carry the signal from the cell surface to the nucleus. (Figure 15–57)

Smad family


Seven-pass transmembrane protein with a structure very similar to a GPCR but does not seem to act as a Hedgehog receptor or as an activator of G proteins; it is controlled by the Patched and iHog proteins.



Family of cytoplasmic tyrosine kinases (pronounced “sark”) that associate with the cytoplasmic domains of some enzyme-linked cell-surface receptors (for example - the T cell antigen receptor) that lack intrinsic tyrosine kinase activity. They transmit a signal onward by phosphorylating the receptor itself and specific intracellular signaling proteins on tyrosines. (Figure 3–10)

Src (Src protein family)


Latent transcription regulator that is activated by phosphorylation by Janus kinases (JAKs) and enters the nucleus in response to signaling from receptors of the cytokine receptor family. (Figure 15–56)

STAT (signal transducer and activator of transcription)


Hormones - including cortisol - estrogen - and testosterone - that are hydrophobic lipid molecules derived from cholesterol that activate intracellular nuclear receptors.

steroid hormones


G protein that - when activated - activates the enzyme adenylyl cyclase and thus stimulates the production of cyclic AMP. (Table 15–3 - p. 846)

stimulatory G protein (Gs)


Intercellular signaling performed by neurons that transmit signals electrically along their axons and release neurotransmitters at synapses - which are often located far away from the neuronal cell body.

synaptic signaling


Large - serine/threonine protein kinase that is activated by the PI-3-kinase–Akt signaling pathway and promotes cell growth.



Large family of structurally related secreted proteins that act as hormones and local mediators to control a wide range of functions in animals - including during development. It includes the TGFβ/activin and bone morphogenetic protein (BMP) subfamilies. (Figure 15–57)

transforming growth factor-β superfamily (TGFβ superfamily)


see G protein

trimeric GTP-binding protein


Enzyme that phosphorylates specific proteins on tyrosines.

tyrosine kinase


Cell-surface receptor that functions similarly to RTKs - except that the kinase domain is encoded by a separate gene and is noncovalently associated with the receptor polypeptide chain.

tyrosine-kinase-associated receptor


Member of a family of secreted signal proteins that have many different roles in controlling cell differentiation - proliferation - and gene expression in animal embryos and adult tissues.

Wnt protein


Signaling pathway activated by binding of a Wnt protein to its cell-surface receptors. The pathway has several branches. In the major (canonical) branch - activation causes increased amounts of β-catenin to enter the nucleus - where it regulates the transcription of genes controlling cell differentiation and proliferation. Overactivation of the Wnt/β-catenin pathway can lead to cancer. (Figure 15–60)

Wnt/β-catenin pathway