Lehninger Principles of Biochemistry- Chapter 12 Key Terms Questions Answered Correctly Graded A+ (Latest Update 2024)
signal transduction - Answers The process by which an extracellular signal (chemical, mechanical, or electrical) is amplified and converted to a cellular response.
specificity - ...
signal transduction - Answers The process by which an extracellular signal (chemical, mechanical, or
electrical) is amplified and converted to a cellular response.
specificity - Answers The ability of an enzyme or receptor to discriminate among competing substrates
or ligands.
cooperativity - Answers The characteristic of an enzyme or other protein in which binding of the first
molecule of a ligand changes the affinity for the second molecule. In positive cooperativity, the affinity
for the second ligand molecule increases; in negative cooperativity, it decreases.
amplification - Answers The action of making something more marked or intense.
enzyme cascade - Answers A series of reactions, often involved in regulatory events, in which one
enzyme activates another (often by phosphorylation), which activates a third, and so on. The effect of a
catalyst activating a catalyst is a large amplification of the signal that initiated the cascade.
modularity - Answers The degree to which a system's components may be separated and recombined,
often with the benefit of flexibility and variety in use.
scaffold proteins - Answers Noncatalytic proteins that nucleate formation of multienzyme complexes by
providing two or more specific binding sites for those proteins.
desensitization - Answers A universal process by which sensory mechanisms cease to respond after
prolonged exposure to the specific stimulus they detect.
integration - Answers The coordination of processes in a system.
response localization - Answers The process of making a biochemical response local in character or
restricting it to a particular place.
G protein-coupled receptors (GPCRs) - Answers A large family of membrane receptor proteins with
seven transmembrane helical segments, often associating with G proteins to transduce an extracellular
signal into a change in cellular metabolism.
guanosine nucleotide-binding proteins - Answers A large family of GTP-binding proteins that act in
intracellular signaling pathways and in membrane trafficking. Active when GTP is bound, they self-
inactivate by converting GTP to GDP. Also called G proteins.
G proteins - Answers A large family of GTP-binding proteins that act in intracellular signaling pathways
and in membrane trafficking. Active when GTP is bound, they self-inactivate by converting GTP to GDP.
Also called guanosine nucleotide-binding proteins.
second messenger - Answers An effector molecule synthesized in a cell in response to an external signal
(first messenger) such as a hormone.
, agonist - Answers A compound, typically a hormone or neurotransmitter, that elicits a physiological
response when it binds to its specific receptor.
antagonist - Answers A compound that interferes with the physiological action of another substance
(the agonist), usually at a hormone or neurotransmitter receptor.
β-adrenergic receptors - Answers A class of G protein-coupled receptors that are targets of many
catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the
body.
heptahelical receptors - Answers Also known as G protein-coupled receptors (GPCRs), a large protein
family of receptors that detect molecules outside the cell and activate internal signal transduction
pathways and, ultimately, cellular responses.
stimulatory G protein (Gₛ) - Answers A trimeric regulatory GTP-binding protein that, when activated by
an associated plasma membrane receptor, stimulates a neighboring membrane enzyme such as adenylyl
cyclase; its effects oppose those of Gᵢ.
adenylyl cyclase - Answers An enzyme which catalyzes the cyclization of adenosine triphosphate (ATP)
into cyclic adenosine monophosphate (cAMP) which requires the cleavage of pyrophosphate (PPᵢ).
cAMP-dependent protein kinase (protein kinase A; PKA) - Answers A family of enzymes whose activity is
dependent on cellular levels of cyclic AMP.
P loop - Answers A motif in proteins that is associated with phosphate binding.
GTPase activator protein (GAP) - Answers Regulatory proteins that bind activated G proteins and
stimulate their intrinsic GTPase activity, speeding their self-inactivation.
regulator of G protein signaling (RGS) - Answers A protein structural domain that stimulates the GTPase
activity of heterotrimeric G proteins.
guanosine nucleotide-exchange factor (GEF) - Answers Regulatory proteins that bind to and activate G
proteins by stimulating the exchange of bound GDP for GTP.
consensus sequence - Answers A DNA or amino acid sequence consisting of the residues that most
commonly occur at each position in a set of similar sequences.
β-arrestin (βarr; arrestin 2) - Answers Intracellular protein that participates in agonist-mediated
desensitization of G protein-coupled receptors and causes specific dampening of cellular responses to
stimuli such as hormones, neurotransmitters, or sensory signals, as well as having signalling roles in its
own right.
G protein-coupled receptor kinases (GRKs) - Answers A family of protein kinases that phosphorylate Ser
and Thr residues near the carboxyl terminus of G protein-coupled receptors, initiating their
internalization.
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