Receptor Quiz

Front 1

There are two important components in the hardware responsible for maintaining resting potential of a cell. One is the so-called Na+/K+ ATPase. What is the other component?

Back 1

K+ leak channels

Front 2

In general ligand-operated ion channels display less ion specificity than voltage-operated channels (i.e. which ion they allow to pass through the pore). This is because:

Back 2

Ligand-operated ion channels have more subunits, thus wider pores

Front 3

If a K+ leak channel opens in a cell that is at its resting potential, in which direction do the K+ ions flow:

Back 3

Out of the cell, causing a hyperpolarization

Front 4

The resting potential for a cell is generally in the range:

Back 4

-50 mV to -70 mV

Front 5

What determines the direction an ion will flow through an ion channel on the membrane of cells?

Back 5

The chemo-equlibrium point of the ion, which depends on both the concentration gradient of the ion and on the charge of the ion

Front 6

The four different subunit types of the nicotinic receptor are structurally very similar. This is because:

Back 6

Their genes are believed to have been derived from the same ancestral gene.

Front 7

Producing a hydropathy profile of a protein can be useful because:

Back 7

A. One can determine if the protein has potential membrane spanning regions
B. One can predict from the profile which end of the protein will be the N-terminal and which end will be the C-terminal.
C. One can use the profile to predict if the protein has evolved from an accessorial gene.
D. All of the above.

Front 8

The enzyme reverse transcriptase is used to produce a cDNA library. This enzyme:

Back 8

Transcribes RNA into DNA

Front 9

ite-directed mutagenesis is a method that is often used when molecular biologists are testing models of receptors (e.g. studying functional domains). In site-directed mutagenesis:

Back 9

A nucleotide within cDNA is altered (substituted for another) so there is an alteration in a codon within the cDNA and thus ultimately which amino acid will be found in the protein

Front 10

Orphan receptors are receptors that:

Back 10

Are predicted to be receptors from their structure but have no known ligand

Front 11

Which amino acid would you expect to find frequently in the ion pore domain of an ion channel?

Back 11

Serine

Front 12

Which amino acid would you expect to find in the ion filter domain of the GABAa receptor.

Back 12

Lysine

Front 13

The enzyme glutamic acid decarboxylase is an important enzyme because:

Back 13

It is responsible for producing an inhibitory neurotransmitter

Front 14

Serines and threonines on intracellular loops of receptors are often targets for:

Back 14

Kinases

Front 15

Benzodiazepines have a “calming” or sedative effect because:

Back 15

They potentiate the actions of GABA

Front 16

For most ion channel receptors, the transmembrane segments of all the subunits contribute in the formation of the ion pore. Glutamate ionotropic receptors are an exception to this. For these receptors the pore is formed from:

Back 16

Each subunit contributes a P-element, which pushes into the membrane to form a pore

Front 17

Among the glutamate ionotropic receptors the N-methyl D-aspartate (NMDA) receptor is considered somewhat unique because:

Back 17

It is highly permeable to Ca2+ and is therefore considered to be a ligand-operated Ca2+ channel

Front 18

The NMDA receptor has the amino acid glycine as a “co-agonist” but glutamate is generally considered to be the neurotransmitter responsible for activating the receptor. Why is glutamate and not glycine generally considered the neurotransmitter for regulating NMDA receptor activity?

Back 18

Because the extracellular concentration of glycine is sufficient to keep the glycine binding site occupied, thus making glutamate, and not glycine, the critical factor for activating the receptor

Front 19

The NMDA receptor is constructed from NR1 and NR2 subunits. Which subunit possesses the binding site for glutamate?

Back 19

The NR2 subunit

Front 20

When a voltage-operated Ca2+ channel opens it forms a microdomain of Ca2+ inside the cell (rather than a massive, widely dispersed Ca2+ signal). This microdomain forms because:

Back 20

A. There are pumps on the membrane to immediately pump the Ca2+ out of the cell, thus not allowing a massive Ca2+ signal to develop
B. The Ca2+ is pumped into the lumen of the endoplasmic reticulum, thus not allowing a massive Ca2+ signal to develop
C. The Ca2+ binds to Ca2+ binding proteins in the cytoplasm, thus not allowing a massive Ca2+ signal to develop
D. All of the above

Front 21

The concentration of the ion Ca2+ is carefully regulated in a cell because:

Back 21

High Ca2+ is toxic to the cell

Front 22

Ca2+-induced Ca2+-release (CICR) is a process whereby:

Back 22

Ca2+ induces a mobilization of Ca2+ from intracellular Ca2+ stores

Front 23

The NMDA receptor is considered a “coincidence detector” because:

Back 23

It can detect the presence of extracellular glutamate, occurring (almost) simultaneously with a membrane depolarization

Front 24

Some neurons are capable of “back propagation” of the action potential (propagation into the dendrites). Such back propagation is important because it:

Back 24

Allows neurons to signal in both directions, adding to the efficiency of neuronal communication

Front 25

The subunits of voltage-operated channels (K+, Na+ and Ca2+) display a high degree of homology. The reason for this is believed to be:

Back 25

A. Because they are all derived from voltage operated Na+ channels (i.e. Na+ channels were the first to arise, giving rise to all other channel types)
B. Prokaryotic inward rectifier K+ channels gave rise to all voltage-operated channels
C. Primitive G protein-coupled receptors evolved into the voltage-operated channels
D. None of the above

Front 26

Post-synaptic density protein 95 (PSD95) is:

Back 26

An intracellular protein which anchors NMDA receptors within the synapse

Front 27

Which group, on the side chain of amino acids within proteins, does Protein kinases phosphorylate?

Back 27

The hydroxyl group

Front 28

The serine/threonine kinases are called serine/threonine because:

Back 28

There are many serines and threonines within the active (catalytic) site of these kinases

Front 29

Serine/threonine kinases are generally found in the cytoplasm of a cell, where they are often regulated by:

Back 29

Second messenger molecules generated by other enzymes

Front 30

Tyrosine kinase receptors are generally found:

Back 30

On the plasma membrane, where they can bind with extracellular ligands and phosphorylate intracellular proteins

Front 31

The ligand binding site of tyrosine kinase receptors often possess disulphide bridges. The purpose of these disulphide bridges is:

Back 31

To form a pocket for ligand binding

Front 32

Tyrosine kinase receptors possess only one transmembrane domain and yet they are quite stable within the membrane (i.e. they do not become detached very easily from the membrane). This is because:

Back 32

They possess positively charged amino acids near the membrane spanning region (transmembrane region) which hold them in place

Front 33

Tyrosine kinase receptors possess only one transmembrane domain and yet, with ligand binding, they are able to transducer a signal across the membrane. They can do this because:

Back 33

Ligand binding induces transmembrane regions of the receptors to fold, thus inducing a structural change in the catalytic domain of the receptor

Front 34

The intracellular domain of tyrosine kinase receptors possess a large number of tyrosines. The purpose of these tyrosines is:

Back 34

To act as a target for tyrosine kinases

Front 35

Substrates for tyrosine kinase receptors possess Src homology region 2 (SRC-2) domains. The purpose of these domains is:

Back 35

To target the substrate to tyrosine kinase receptors

Front 36

Viral Src (vSRC) is:

Back 36

An oncogene coding for a tyrosine kinase

Front 37

When a tyrosine kinase receptor is activated the first protein that it phosphorylates is:

Back 37

Another tyrosine kinase receptor molecule, thus producing substrate recognition sites within the kinase

Front 38

In phosphorylations catalyzed by tyrosine kinase receptors, the source of the phosphorous is:

Back 38

ATP

Front 39

The activation of GTPase activating protein (GAP) by tyrosine kinase receptors will in turn:

Back 39

Inactive G proteins, thus inhibiting G protein signaling

Front 40

Phospholipase C gamma (PLCγ) is an enzyme which:

Back 40

Catalyzes the breakdown of membrane phospholipids

Front 41

Diacylglycerol (DAG) is a lipid that:

Back 41

Can bind to and activate a kinase

Front 42

Protein kinase C (PKC) is a kinase that:

Back 42

Possesses a binding site for diacylglycerol (DAG)

Front 43

The activation of the IP3 Receptor can:

Back 43

Initiate Ca2+ induced Ca2+ release

Front 44

Phospholipase C-gamma (PLCγ) and PLCβ are:

Back 44

Two different lipases, one activated by tyrosine kinase receptors and the other activated by G protein-coupled receptors

Front 45

When tyrosine kinase receptors are activated by ligands they often undergo “clustering” on the membrane. Such clustering is followed by endocytosis. The function of this endocytosis may be:

Back 45

A. To down-regulate the receptor mechanism, whereby the receptor is send to lysosomes for destruction
B. To desensitize the receptor mechanism, whereby the receptors are temporarily internalized but eventually are returned to the membrane
C. To bring activated receptor into the cell to phosphorylate proteins inside the cell
D. All of the above.

Front 46

Posphatases are enzymes that dephosphorylate proteins. A characteristic of phosphatases is:

Back 46

That their activity, unlike the kinases, is unregulated

Front 47

Viral oncogenes are thought to be derived from the eukaryotic genome because:

Back 47

They possess an intron-exon structure

Front 48

Tropomyosin-receptor kinase (Trk) is a product of a viral oncogene. Proto-oncogenes of Trk represent:

Back 48

Receptors for neurotrophins

Front 49

As the name implies, neurotrophins stimulate neurons. The release of neurotrophins can be constitutive (i.e. via a Ca2+-independent pathway). One of the functions of this constitutive secretion of neurotrophin is:

Back 49

To signal to other brain areas that the neuron is active

Front 50

The source of Ca2+ for the regulated release of neurotransmitters is usually an influx through voltage-operated Ca2+ channels. For the regulated secretion of neurotrophins it would seem that the an important source of Ca2+ is:

Back 50

Ca2+ mobilized from intracellular Ca2+ stores

Front 51

The C-terminal region of Trk receptors can bind dynein, a retrograde transport protein. What possible significance might this finding have concerning Trk receptor signaling?

Back 51

Endosomes, containing activated receptors, could be transported to the cell body of the neuron

Front 52

The effectors proteins of G protein-coupled receptors produce the so-called second messenger molecules. What are the first messengers?

Back 52

Hormones and neurotransmitters that act, via their receptors, on the G proteins.

Front 53

G proteins can be involved in regulating ion channels. They can do this by:

Back 53

Activating effectors to produce second messengers which in turn activate kinases that phosphorylate the ion channel to change ion channel activity

Front 54

The mechanism of action of neuropeptides is:

Back 54

Through G protein-coupled receptors

Front 55

In the β-adrenergic receptor, the binding site for noradrenalin is:

Back 55

Deep within the receptor, within the transmembrane regions

Front 56

Which of the following interactions is not involved in noradrenalin binding to the β-adrenergic receptor?

Back 56

Covalent bonding

Front 57

The G protein binding domain of G protein-coupled receptors is found:

Back 57

Within intracellular loops of the receptor

Front 58

What is the significance for the fact that many serines and threonines are found within the intracellular loops of G protein-coupled receptors?

Back 58

These amino acids can ion pair with acetic amino acids of the transmembrane regions, thus making an mportant contribution to the tertiary structure of the receptor

Front 59

What does glutamate, GABA and Ca2+ have in common?

Back 59

They are all ligands for G protein-coupled receptors

Front 60

Large peptides or even proteins can be ligands for G protein-coupled receptors. In such cases the ligand-receptor interaction usually involves:

Back 60

Binding of the protein to a extracellular ligand-binding domain and then an interaction of a portion of the protein with the transmembrane region to effectuate signal transduction

Front 61

G proteins are called G proteins because:

Back 61

They are GTPases

Front 62

G protein-coupled receptors can be thought of as working like an enzyme because:

Back 62

Similar to enzymes, they are regulated by ligand binding

Front 63

The G protein of a G protein-coupled receptor becomes activated when:

Back 63

There is an exchange of GDP for GTP within the G protein, and the G protein complex dissociates

Front 64

The effector protein for the G protein αq is:

Back 64

Phospholipase-Cβ

Front 65

The effector protein for the G protein αi is

Back 65

Adenylyl cyclase

Front 66

Alpha subunits of G proteins possess:

Back 66

Higher target (effector) specificity than beta/gamma subunits

Front 67

Cone opsins are essentially light sensitive G protein-coupled receptors, activated by light (rather than by e.g. a neuropeptide). What gives the opsins their different light absorbing properties?

Back 67

Each opsin possesses a slightly different light-absorbing retinal molecule, thus accounting for their different light absorbing spectrums

Front 68

The effector protein of rhodopsin is the enzyme phosphodiesterase. Activation of this enzyme leads to:

Back 68

Lower levels of cyclic GMP in the rods, leading to hyperpolariatation of the rods in response to light

Front 69

What is the function of cyclic GMP in sensory transduction by the rod cells of the retinal?

Back 69

It acts directly on cation channels on the membrane of the rod cells, leading to membrane depolarization

Front 70

Cholera toxin and pertussis toxin act on G protein-coupled receptor signaling systems to exert their toxic effects. In their mechanism of action these toxins:

Back 70

Act directly on the G proteins

Front 71

Cellular programs of cells reflect which enzymes are expressed by the cells. These enzymes often drive metabolic pathways. The role of hormones (and often neuropeptides) is to:

Back 71

Regulate the activity of the enzymes, thus regulating the direction and speed of the metabolic pathways

Front 72

There are many isoforms of the enzyme adenylyl cyclase, all of which can be activated by Gs. Some isoforms can are regulated by:

Back 72

Gi

Front 73

While Gi is usually associated with the inhibition of adenylyl cyclase, some forms of adenylyl cyclase are activated with the activation of Gi. This is because:

Back 73

Gi activates other effectors which then activate adenylyl cyclase in an indirect way

Front 74

Some isoforms of adenylyl cyclase can function as coincidence detectors. This coincidence detection can concern:

Back 74

Concurrent stimulation of the cell by two neurotransmitters, one generating activated αs subunits, the other generating a strong β/γ signal

Front 75

there are two forms of guanylyl cyclase, one the so-called soluble form and the other is called the particulate form. The soluble form is called soluble because:

Back 75

In an aqueous extraction of cells, it is found that following centrifugation the cyclase is in the soluble supernatant fraction

Front 76

Both Atrial Natriuretic Peptide (ANP) and nitric oxide (NO) cause vasodilation and a lowering of blood pressure. They do this by:

Back 76

Activating their receptors, which are guanylyl cyclases

Front 77

Nitric oxide synthase (NOS) is a component of a signaling cascade that regulates vasodilation. This enzyme is regulated by:

Back 77

Ca2+ calmodulin kinase II (caMKII)

Front 78

Phospholipase Cβ is a lipase which:

Back 78

Is the effector enzyme for the G protein Gq
B. Degrades the phospholipid phosphtidyinositol 4,5 P2
C. Generates two intracellular second messengers
D. All of the above

Front 79

It is important that second messenger molecules have short half-lives. For the second messenger cyclic AMP there are:

Back 79

Phosphodiesterases in the cytoplasm for the conversion of cyclic AMP to AMP

Front 80

It is important that second messenger molecules have short half-lives. For the second messenger inositol triphosphate (IP3) there are:

Back 80

Phosphatases in the cytoplasm for breaking down IP3

Front 81

In general protein kinase A (PKA) has a much greater working range that protein kinase G (PKG). This is because:

Back 81

The catalytic domains of PKA come free from the regulatory domains and are free to diffuse throughout the cell whereas for PKG the regulatory and catalytic domains are within one large (and thus less diffusible) protein

Front 82

Phosphatidyl serine (PtdSer), Ca2+ and diacylglycerol (DAG) all have binding sites in the regulatory domain of protein kinase C (PKC), but DAG is considered the physiological regulatory of the enzyme. This is because:

Back 82

PtdSer and Ca2+ are usually present at sufficiently high levels to support enzyme activity whereas DAG is not

Front 83

The protein calmodulin is:

Back 83

A. Present at high concentration in every cell
B. A Ca2+ binding protein that undergoes a structural change upon Ca2+ binding
C. Highly conserved

Front 84

Ca2+ calmodulin kinase II (CaMKII) is considered a kinase with a “memory” because:

Back 84

It can be transphosphorylated, thereby putting the enzyme in Ca2+ independent active state

Front 85

In a dopaminergic nerve terminal a Ca2+ microdomain can induce exocytosis and activate Ca2+ calmodulin kinase (CaMK). The CaMK can in turn:

Back 85

Phosphorylate the protein synapsin 1

Front 86

Ca2+ calmodulin kinase II (CaMKII) often occurs in a complex containing 12 CaMKII molecules. The functional importance of this complex formation is:

Back 86

To increase the probability of transmolecular phosphorylation, and thus aid the functioning of CaMKII as a “memory”molecule

Front 87

Ca2+ calmodulin kinase II (CaMKII) can exist as a monomer or as complex containing 12 CaMKII molecules. Which form a cell possesses depends on:

Back 87

Whether the CaMKII isoform expressed by the cell possesses the “self-association” domain or not

Front 88

G protein-coupled receptor mechanisms have been termed “metabotropic” because the phosphorylations they induce (via activation of kinases) can affect the metabolism of a cell. The consequences can last for many days (or even years) because:

Back 88

The proteins phosphorylated by G protein signaling cascades can be transcription factors which bring about changes in gene expression and thus long term changes to the cell

Front 89

A kinase anchoring proteins (AKAPs) can be involved in constructing supramolecular signaling complexes. They are called AKAPs because:

Back 89

They all bind PKA (and many can bind other proteins such as other kinases and/or phosphatases)

Front 90

The constraints of signaling domains on the membrane can add to the versatility of the G protein coupled receptor mechanisms to generate diverse signals. This is because:

Back 90

A. The cell, through the construction of domains with different receptors and G proteins, can control what its (unambiguous) response will be to activation by particular receptor mechanisms
B. The signaling domains allow a cell to keep phosphatases compartmentalized from kinases and thus avoids interactions between these two classes of signaling proteins
C. The signaling domains provide a site for downstream signaling components, such as the kinases, to insert themselves into the membrane, thus becoming part of the signaling complex

Front 91

The transcription factor CREB received its name for the fact that it can be activated by cyclic-AMP signaling pathways (Cyclic AMP Responsive Element Binding protein). This transcription factor:

Back 91

Acts directly on the transcriptional machinery following its binding to CRE

Front 92

DREAM is a transcription factor which suppresses gene expression. Its binding to its downstream responsive element is lifted through:

Back 92

Ca2+ binding directly to the factor

Front 93

C-fos is an immediate early gene. The “c-fos method” is based on the premise that:

Back 93

This immediate early gene come to expression in cells that were just activated and that this expression is transitory (thus showing a positive signal in cells that have just been activated)

Front 94

There are binding proteins in the blood for most steroid hormones. The function of these binding proteins might be to:

Back 94

Aid in the release of the hormone from the steroid producing endocrine cells

Front 95

The enzyme cholesterol ester hydrolase (CEH) is the rate-limiting enzyme for the production of steroid hormones. For glucocorticoid production in the adrenal gland this enzyme is regulated by:

Back 95

A signaling cascade involving protein kinase A (PKA) phosphorylation which activates CEH

Front 96

The glucocorticoid receptor is a transcription factor. This transcription factor can:

Back 96

A. Bind to glucocorticoid responsive elements (GRE) to promote gene expression
B. Bind to negative glucocorticoid responsive elements (nGRE) to repress gene gexpression
C. Bind to and interfere with other transcription factors to inhibit gene expression

Front 97

The synthesis and release of glucocorticoids, sex steroids and thyroxine are all regulated by factors (hormones) released from the pituitary gland. The production and release of the pituitary factors can be regulated by feedback loops. These feedback loops:

Back 97

Can be directed to the hypothalamus or to the pituitary gland (or to both)