comparative studies of mitochondrial DNA
	comparative studies of ribosomal RNA
	the fossil record
	the study of protein receptors embedded in the nuclear membrane
	the similarity of the mechanisms in organisms that have a very distant common ancestor

	neurotransmitter
	transcription factor
	protein kinase
	local regulator
	G protein

	the signal molecule combined directly with a cytosolic enzyme to form an active quaternary structure
	the signal molecule worked equally well with intact or disrupted cells
	the signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated
	the cell-signaling pathway involves two separate steps: transduction and response
	epinephrine is involved in response to stress

	kill other yeast cells nearby, which may be competing for access to food
	kill bacteria nearby, which may be competing for access to food
	stimulate an α yeast cell to grow toward the α cell
	attract other yeast cells of the same mating type to assemble
	enzymatically process food into a form that can be easily absorbed

	numerous cells can receive and respond to a signal produced in their vicinity
	the signal can be directed to a very specific target because a narrow space separates the target cell from the transmitting cell
	a concentration gradient between the signaling cell and its target cells is established, causing cells along the gradient to respond in different ways
	specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected
	special molecules are passed through cell junctions

	Nontarget cells possess enzymes that immediately degrade the molecules as they enter the cell.
	Nontarget cells lack the inactive enzymes that the signal molecules activate.
	Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus.
	The signal molecules diffuse from the cell before an effective concentration can be achieved.
	In nontarget cells these signal molecules cross the membranes of the endoplasmic reticulum and are captured by vesicles.

	are not an example of signaling molecules
	do not bind to receptors
	directly bind to DNA
	do not initiate cell signaling by interacting with a receptor in the plasma membrane.
	act by phosphorylating DNA

	α protein
	ligand
	protein kinase
	competitive inhibitor
	DAG

	all work via protein kinases
	are never found in the nucleus of a cell
	can be found as part of the plasma membrane or found within the cytoplasm
	all work by opening ion channels
	are only found associated with the plasma membrane

	testosterone cannot cross the plasma membrane
	not all cells in the body have membrane receptors for testosterone
	it is a local regulator
	it affects only cells that have ion-channel receptors
	not all cells have cytoplasmic receptors for testosterone

	act by phosphorylating a protein ... open an ion channel when bound to a signal molecule
	are transmembrane proteins ... are found only on the cytoplasmic side of the plasma membrane
	are not enzymes ... have enzymatic function
	form a dimer when activated ... catalyze the transfer of a phosphate group from ATP to an amino acid
	phosphorylate the amino acid guanine ... phosphorylate the amino acid threonine

	ion-channel receptors
	protein phosphatase receptors
	G-protein-linked receptors
	adenylyl cyclase receptors
	tyrosine-kinase receptors

	phosphorylates an amino acid
	results in the formation of a dimer
	promotes the binding of a steroid hormone to its receptor in the cytoplasm
	alters the expression of genes, especially in neurons
	affects the membrane potential

	enters the cell via a protein channel
	acts by directly binding to DNA
	binds to both membrane receptors and cytoplasm receptors
	is a gas
	activates proteins by removing phosphate

	GDP replaces GTP
	it is bound by its ligand and transported to the nucleus
	GTP is bound to it
	it is phosphorylated by protein kinase
	Ca2+ binds to a G-protein-linked receptor

	ion-channel
	G-protein
	tyrosine-kinase
	adenylyl cyclase
	calmodulin

	the inactivation of ligand-gated ion channels
	the inactivation of G-protein-linked signaling pathways
	that the activated G proteins would remain locked in the "on" position, transmitting signal even in the absence of signaling molecule
	the inhibition of pathways stimulated by tyrosine-kinase receptors
	receptor tyrosine kinases would be stimulated by the additional phosphate groups present in the modified GTP

	hydrolysis of GTP to GDP
	hydrolysis of GDP to GTP
	phosphorylation of GDP to GTP
	replacement of GDP with GTP
	phosphorylation of GTP to GDP

	inhibits the enzyme that normally breaks down cAMP
	prevents G-protein inactivation, which leads to the continuous production of cAMP
	inhibits adenylyl cyclase, preventing the cell from producing cAMP
	blocks the receptor site for cAMP
	phosphorylates the cAMP, producing ADP

	the synthesis of mRNA
	the activation of an inactive enzyme
	alteration of the cytoskeleton
	a change in the chemical composition of the cytosolic environment
	the activation of a metabolic pathway

	Glucagon breaks down glycogen to glucose in liver cells.
	The hormone that breaks down glycogen into glucose enters the liver cell.
	The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell.
	Glucose is produced from glycogen when epinephrine binds to a cytoplasmic protein.
	A cytoplasmic receptor triggers the signal transduction pathway that produces glucose from glycogen.

	protein dehydrogenase
	protein phosphatase
	protein kinase
	peptidase
	protein cyclase

	always inactivates a protein
	activates G-protein-linked receptors
	can either activate or inactivate a protein
	is accomplished by protein phosphatases
	always activates a protein

	cAMP
	ATP
	protein kinase
	GTP
	protein phosphatase

	rapidly cross the plasma membrane
	rapidly move throughout the cell by diffusion
	pass quickly from cell to cell
	move from substrate to substrate during a phosphorylation cascade
	cross the nuclear membrane and interact with DNA

	phosphodiesterase
	receptor tyrosine kinases
	G proteins
	adenylyl cyclase
	protein kinase A

	are far more abundant in the cytoplasm compared to blood and other extracellular fluid
	are rapidly transported into the endoplasmic reticulum in response to G-protein-mediated signals
	are often concentrated within the endoplasmic reticulum
	are not very widely used as second messengers
	all of the above

	calcium—IP3
	cAMP—adenylyl cyclase
	cAMP—protein kinase A
	DAG—IP3
	all of the above

	is always present at high levels in the cytosol ... is present at low levels in the absence of a signal
	is synthesized by an enzyme in response to a signal ... released from intracellular stores
	is stored in the endoplasmic reticulum ... is never stored in the cell
	is tyrosine-kinase-receptor linked ... is G-protein-receptor linked
	enters the cell via a transmembrane protein channel ... enters the cell by diffusing across the plasma membrane

	protein kinase A activation
	Ca2+
	the cleavage of PIP2
	DAG
	phospholipase C

	activating cAMP
	phosphorylating signal receptors
	opening Ca2+ channels
	activating PIP2
	activating DAG

	blood
	extracellular fluid
	mitochondria
	endoplasmic reticulum
	lysosomes

	glycogen
	cyclic AMP
	tRNA
	epinephrine
	glucose

	binding of a growth factor to its receptor ® activation of transcription factor ® phosphorylation cascade ® transcription
	binding of a growth factor to its receptor ® phosphorylation cascade ® activation of transcription factor ® transcription
	G-protein activation ® phosphorylation cascade ® binding of a signaling molecule to its receptor ® activation of transcription factor ® transcription
	testosterone binds to its receptor ® G-protein activation ® adenylyl cyclase activation ® levels of cAMP in the cytoplasm rise
	binding of a signaling molecule to a receptor tyrosine kinase ® phosphorylation of G protein ® adenylyl cyclase activation ® levels of cAMP in the cytoplasm rise

	muscle cells lack the appropriate membrane receptor
	a multifunctional relay protein involved with the proliferation of immune cells is defective
	nerve cells lack the ability to produce cAMP
	G proteins are unable to phosphorylate GDP
	the endoplasmic reticulum is unable to store calcium

	the signal is reduced
	the number of molecules involved decreases
	the number of molecules involved remains constant
	the signal is amplified
	glycogenesis is stimulated

	there are differences in the proteins found in the two types of cells
	the GI tract does not have epinephrine receptors
	in cells of the GI tract epinephrine operates via a cytosolic receptor, whereas in cells of the heart epinephrine acts via a plasma membrane receptor
	the concentration of Ca2+ is lower in the cytosol of GI-tract cells than in the cytosol of heart cells
	cells of the GI tract lack cAMP