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PBD > Receptors and Second Messengers > Flashcards

Receptors and Second Messengers Flashcards

1
Q

What is a signaling molecule?

A

A compound produced in one cell, and used to transmit a message to one (or many) other cells

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2
Q

What is a receptor?

A

A specific protein that is the site for binding of a signaling molecule

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3
Q

What is an effector?

A

The protein or mechanism that is ultimately activated by a receptor

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4
Q

What is a second messenger?

A

A small intracellularly diffusible signaling molecule. In G protein signaling systems, second messengers are modulated by primary effectors

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5
Q

What is a ligand?

A

A compound that binds to a specific site on a protein. A subtype of signaling molecule.

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6
Q

What is an agonist?

A

A ligand that binds to a receptor and activates the effector

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7
Q

What is an antagonist?

A

A ligand that binds to a receptor but does not activate effector. Prevents agonists from binding to receptor.

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8
Q

What is a full agonist?

A

Binds to receptor and fully activates effector

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9
Q

What is a partial agonist?

A

Binds to a receptor but only partially activates effector

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10
Q

What is an inverse agonist?

A

Binds to receptor and inactivates (turns off) effector (produces the opposite effect as an agonist)

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11
Q

What is a competitive antagonist?

A

Competes with an agonist for the same binding site on a receptor

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12
Q

What is a non-competitive antagonist?

A

Binds to a receptor at a discrete site and changes the maximal response without altering the potency

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13
Q

What is the difference between an inverse agonist and an antagonist?

A

Inverse agonist still does something to the effector. Antagonist does not.

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14
Q

What are the four types of signaling between cells?

A

Contact dependent, paracrine, synaptic, and endocrine

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15
Q

Describe contact dependent signaling

A

Signaling molecule is NOT diffusible. Cells must be in direct contact. Important during development and for some types of immune function.

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16
Q

Describe paracrine signaling

A

Signaling molecules are released into the extracellular space, where they may act on cells that express receptors for the signaling molecule. Paracrine signals may be terminated by cells that take up and/or enzymes that break down the signaling molecule.
ACTS LOCALLY

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17
Q

Describe synaptic signaling

A

Allows very specific and very RAPID delivery of HIGHLY concentrated signaling molecules at large distances from the cell soma. The primary signaling molecules released from synaptic terminals are neurotransmitters.

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18
Q

Describe endocrine signaling

A

Allows relatively SLOW and non-specific delivery at LOW concentrations via the BLOODstream. The signaling molecules released from endocrine cells are HORMONES.

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19
Q

What are the two major classes of receptors?

A

Cell surface receptors (exist on/in the plasma membrane) and cytosolic/nuclear receptors (found inside the cell)

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20
Q

What are the three classes of cell surface receptors? Which two are the most important?

A

Ion linked, G-protein linked, and Enzyme linked

Ion and G-Protein linked are the most important

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21
Q

Ion channel linked receptors are also known as…

A

ligand gated ion channels and ionotropic receptors

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22
Q

Ligand gated ion channels are gated by a small number of ligands called…

A

Neurotransmitters (e.g. glutamate, GABA, glycine, acetylcholine, serotonin, etc)

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23
Q

True or False: Ligand gated ion channels are selective for certain ions.

A

True and False…can be selective, can be non-selective

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24
Q

When ligand gated ion channels open, the ions will flow (with/against) their concentration gradient

A

With

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25
Q

What are the four mechanism types described for ion channels?

A

Voltage-gated, Ligand-gated (ionotropic), membrane de-limited metabortropic (binds to a receptor, receptor tells protein, protein tells channel), and diffusible second messenger metabotropic (binds to receptor, receptor tells protein, protein tells enzyme, enzyme tells second messenger, second messenger tells channel)

26
Q

STRUCTURE: Most ligand gated ion channels are _______, meaming they are constructed from _____ distinct subunits. Some subunits are ____, others are _____.

A

Pentameters; five; structural; ligand binding

27
Q

Why is there so many variations of ligand gated ion channels?

A
  • Most receptors are composed of 5 subunits, but there are often more than 5 types of subunits that could be used to make that receptor
  • There are multiple versions of each type of subunit
  • Multiple combinations of subunits may combine to make functional receptors
28
Q

Nicotine binds to _________ in the ___.

A

Nicotinic acetylcholine receptors; CNS

29
Q

Barbiturates and tranquilizers bind to ______ and potentiate their function by _______ sensitivity of the receptor to ______.

A

GABA receptors, increasing, GABA

30
Q

________ compounds lower blood pressure, relieve chest pain, correct irregular heartbeats, and prevent migraines

A

β-andrenergic compounds

31
Q

Prozac is a _________ inhibitor.

A

Secretion reuptake

32
Q

What proteins form the largest family of all cell-surface receptors and are found in all eukaryotes?

A

G-proteins

33
Q

In mice, ~____ g-protein coupled receptors are involved in the sense of smell alone

A

1000

34
Q

True or False: One ligand can often activate more than one type of G-protein coupled receptor

A

True (up to 15 are activated by serotonin)

35
Q

How many known drugs work through G-protein coupled receptors?

A

About half

36
Q

G-protein coupled receptors are single long _______ chains that have _ transmembrane spanning regions

A

Polypeptide; 7

37
Q

Describe the mechanism of generalized G-protein coupled receptor

A

Receptor binds to G-protein receptor
Receptor associates with inactive G protein
Activated receptor causes inactive G-protein to exchange GDP for GTP
G-protein breaks into 2 active units: alpha and beta+gamma
Active alpha subunit binds to target protein
GTP is hydrolyzed, causes dissociation from target protein
Inactive alpha reassembles with beta+gamma complex

38
Q

The g-protein coupled receptor stays active as long as…

A

Ligand is bound

39
Q

What is the primary effector and second messenger of Gs and Gi?

A

Primary effector: Adenylyl cyclase

Second messenger: Cyclic AMP

40
Q

What is the primary effector and second messenger of Gq?

A

Primary effector: Phospholipase C

Second messenger: Inositol triphosphate

41
Q

What is the primary effector and second messenger of Gi (beta+gamma subunit)?

A

Primary effector: Ion channels

Second messenger: Ions

42
Q

What is the primary effector and second messenger of Gt?

A

Primary effector: cGMP phosphodiesterase

Second messenger: cGMP

43
Q

Why is the cAMP g-protein pathway important?

A

Because cAMP can activate protein kinase A

44
Q

Cyclic AMP is synthesized from ATP by _________. It is broken down by _________.

A

Adenylyl cyclase; cyclic AMP phosphodiesterases

45
Q

What does Protein Kinase A do?

A

Transfers terminal phosphate from ATP to specific serine and threonine residues on target proteins, thereby regulating their function. The phosphates are removed by serine threonine phosphoprotein phosphatases.

46
Q

What does cAMP break down to?

A

adenosine 5’ monophosphate

47
Q

What does activated PKA do?

A

It activates CREB (cAMP response element binding protein) which binds to a CREB binding element on DNA, which increases or decreases transcription of the genes downstream

48
Q

Where is PKA activated? Where does activated PKA go?

A

PKA is activated in the cytosol. Activated PKA can go through nuclear pores into the nucleus, where it binds to CREB.

49
Q

Describe the phospholipase C g-protein pathway

A

Phospholipase C (PC) is activated by Gq
Activated PC breaks down phsphatidylinositol 4,5-bisphosphate into two active signaling molecules, IP3 and DAG
IP3 dissociates from the membrane and enters the cytosol where it binds to IP3 receptors on the smooth ER and causes a release of stored calcium
DAG stays associated with the membrane and activates protein kinase C. The Ca2+ released from IP3 also goes to protein kinase C, which activates it. (Needs both DAG and calcium to be activated)

50
Q

Why is IP3 a second messenger, but DAG isn’t?

A

Because IP3 becomes unbound from the membrane and enters the cytosol. DAG stays bound to the membrane.

51
Q

What does the beta+gamma Gi protein do?

A

Interacts with K+ channels in the cardiac cell plasma membrane, opening them. This makes it harder to depolarize (excite) the cell.

52
Q

Muscarinic acetylcholine receptors activate…

A

Gi

53
Q

The photosensitive cells of the retina are called…

A

Rods and cones

54
Q

Rods are highly sensitive to light and are good for night vision. Their rate of transmitter release is modulated by their __________. When light is low, high concentrations of ____ keep Na+ conductive channels open and promote transmitter release. When light levels go up, G-protein _____ is activated, which catalyzes _______. This leads to closing of Na+ channels.

A

Membrane potential; cGMP; transducin; breakdown of cGMP.

55
Q

Enzyme linked receptors are _______ proteins, with an _______ binding domain.

A

Transmembrane; extracellular

56
Q

Most enzyme linked receptors have _ transmembrane domains.

A

1

57
Q

The (cytosolic/extracellular) side of an enzyme linked receptor has enzymatic activity itself, or is directly associated with an enzyme

A

Cytosilic

58
Q

There are _ major classes of enzyme linked receptors, most are…

A

6

Receptor tyrosine kinases, tyrosine phosphatases, serine/threonine kinases, or guanylyl cyclases

59
Q

Cytosolic and nuclear receptors can be bound by _____ molecules. These include….

A

Small nonpolar; steroid hormones, thyroid hormones, and vitamin D

60
Q

When cytosolic and nuclear receptors are activated by signaling molecules, they bind to ______ and regulate ______.

A

DNA; transcription of specific genes

61
Q

Cytosolic/nuclear receptors are….

A

ligand activated gene regulatory proteins

PBD (7 decks)

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