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Biochem > Chapter 13.3 > Flashcards

Chapter 13.3 Flashcards

1
Q

G-protein-coupled receptors contain … and undergo … when a hormone binds

A

seven membrane-spanning helices; conformational changes

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2
Q

agonist binding to a G-protein-coupled receptor induces the alpha subunit of the associated heterotrimeric G protein to exchange … for … and dissociate from the beta and gamma subunits

A

GDP; GTP

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3
Q

… is activated to produce cAMP, which in turn activates protein kinase A

A

adenylate cyclase

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4
Q

signaling activity is limiting through the action of … that act on cAMP and cGMP

A

phosphodiesterases

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5
Q

…: proteins that are members of the superfamily of regulatory GTPases known as G proteins which bind the guanine nucleotides GTP and GDP and hydrolyze GTP

A

heterotrimeric G proteins

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6
Q

the monomeric G proteins are essential for:
…
…
the growth of …
… (as ribosomal accessory factors)
… (as components of the signal recognition particle and the SRP receptor)

A 
signal transduction 
vesicle trafficking
actin microfilaments
translation 
protein targeting
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7
Q

(components of heterotrimeric G proteins) …: transmembrane proteins that bind their corresponding agonist on their extracellular side, which induces a conformational change on their cytoplasmic side

A

G-protein-coupled-receptors

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8
Q

(components of heterotrimeric G proteins) heterotrimeric G proteins, which are anchored to the … side of the plasma membrane and which are activated by a GPCR when it binds its corresponding agonist

A

cytoplasmic

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9
Q

(components of heterotrimeric G proteins) …: a transmembrane enzyme that is activated (or in some cases inhibited) by activated heterotrimeric G proteins

A

adenylate cyclase

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10
Q

activated AC (adenylate cyclase) catalyzes the synthesis of … (…) from ATP

A

adenosine-3’-5’-cyclic monophosphate (cAMP)

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11
Q

cAMP is a …: that is, it intracellularly transmits the signal originated by the extracellular ligand

A

second messenger

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12
Q

GPCRs have essential … functions, constituting the olfactory and gustatory receptors, as well as the several light sensing proteins in the retina, which are known as …

A

sensory; rhodopsins

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13
Q

the GPCRs are all … membrane proteins with 7 transmembrane alpha helices of generally uniform size: 20-27 residues. their .. and … segments vary in length. these are the portions that participate in binding ligands and heterotrimeric G proteins

A

integral; N- and C- terminal segments

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14
Q

Many GPCRs are modified by n-glycosylation and/or by the palmitoylation of a cys residue, so they are also …

A

lipid-linked glycoproteins

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15
Q

by alternating between two discrete conformations, one with … bound and one without, the GPCR receptor can transmit an extracellular signal to the cell interior

A

agonist

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16
Q

…: G proteins that consist of an alpha, beta, and gamma subunit

A

heterotrimeric G proteins

17
Q

the large alpha subunit of the heterotrimeric G protein consists of two domains connected by polypeptide linkers:

  1. a highly conserved … domain structurally similar to those in monomeric G proteins such as Ras, and is known as a … domain
  2. a … domain unique to them
A

GTPase; Ras-like; helical

18
Q

the beta subunit of the heterotrimeric G proteins consists of an N-terminal helical domain and a C-terminal domain comprising 7 4-stranded antiparallel beta sheets, called a …

A

beta propeller

19
Q

in its unactivated state, a hetertrimeric G protein maintains its heterotrimeric state and its Galpha subunit binds GDP. however, the binding of a Galpha * GDP-Gbeta,gamma complex to its cognate GPCR in complex with an agonist induces the galpha subunit to exchange its bound … for …

A

GDP; GTP

20
Q

when gtp is bound to Galpha, its gamma phosphoryl group promotes conformational changes in three of Galpha’s so called …, causing Galpha to dissociate from Gbeta,gamma –> activation of the G protein
GTP hydrolysis reassembles the inactive form

A

switch regions

21
Q

one of the major targets of the heterotrimeric G protein system is the enzyme …, which the binding of GTP to Galpha activates.

A

adenylate cyclase

22
Q

…: stimulatory G protein

A

Gsalpha

23
Q

inhibitory G proteins:

A

Gialpha

24
Q

bc a single agonist-receptor interaction can activate more than one G protein, this step of the signal transduction pathway serves to … the original extracellular signal

A

amplify

25
Q

cells can adjust their … levels in response to a great variety of stimuli

A

cAMP

26
Q

cAMP is a polar, freely diffusing second messenger. in eukaryotic cells, its main target is … (PKA; also known as … or cAPK), an enzyme that phosphorylates specific Ser/Thr residues of numerous cellular proteins

A

protein kinase A; cAMP-dependent protein kinase

27
Q

the intracellular concentration of cAMP determines the fraction of PKA in its … form and thus the rate at which it .. its substrates

A

active; phosphorylates

28
Q

the phosphoryl group at PKA’s Thr 197 functions to … its active site residues

A

properly orient

29
Q

The R subunit of protein kinase A

A

competitively inhibits its C subunit

30
Q

The R subunit contains two homologus cAMP-binding domains, Ra and Rb, and a so-called …, which blocks substrate binding

A

autoinhibitory segment

31
Q

each step of a signal transduction pathway can potentially be regulated, so the nature and magnitude of the cellular response ultimately reflect the presence and degree of … or … of all the preceding components of the pathway

A

activation; inhibition

32
Q

many drugs and toxins exert their effects by modifying components of the … system

A

adenylate cyclase

33
Q

a hallmark of biological signaling systems is that they adapt to long-term stimuli by reducing their response to them, a process named … These signaling systems therefore respond to … levels rather than to their absolute values

A

desensitization; changes in stimulation

34
Q

active PKA phosphorylates …, which in turn, phosphorylates several intracellular Ser and Thr residues on the C-terminus of the hormone-receptor complex but not on the receptor alone. the phosphorylated receptor binds proteins known as … to form complexes that sterically block the formation of the receptor-Gs complex, resulting in desensitization

A

beta-adrenergic receptor kinase; beta-arrestins

35
Q

in any chemically based signaling system, the signal molecule must eventually be eliminated in order to control the .. and … off the signal and to prevent interference with the reception of ..

A

amplitude; duration; subsequent signals

36
Q

in the case of cAMP, this second messenger is hydrolyzed to AMP by enzymes known as …

A

cAMP-phosphodiesterases

37
Q

The PDE superfamily, which includes both cAMP-PDEs and … is encoded in mammals by at least 20 different genes grouped into 12 families

A

cGMP-PDEs

38
Q

PDEs may be activated by one/more of a variety of agents, including a calcium ion and phosphorylation by PKA and …

A

insulin-stimulated protein kinase

39
Q

PDEs provide a means for crosstalk between … and those using other types of signals

A

cAMP-based signaling systems

Biochem (23 decks)

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