Deck 23: Mechanisms of Signal Transduction

Question 1

In the visual process, activated rhodopsin causes which of the following events to occur?

A)transducin binding to GTP
B)transducin binding to GDP
C)transducin binding to cGMP
D)transducin binding to GMP
E)none of the above

Answer 1

A

Question 2

InsP₃ binds to _______ channels in the endoplasmic reticulum while DAG activates ___________.

A)Na⁺; protein kinase A
B)Na⁺; protein kinase C
C)Ca²⁺; protein kinase A
D)Ca²⁺; protein kinase C
E)none of the above

Answer 2

D

Question 3

Which of the following signaling molecules activate the phosphoinositide second messenger system?

A)platelet-derived growth factor
B)acetylcholine
C)vasopressin
D)thyrotropin-releasing hormone
E)all of the above

Answer 3

E

Question 4

What happens when the GTPase activity of a G protein is blocked?

A)the $\alpha$ subunit associates only with the $\beta$ subunit, not the $\gamma$ subunit
B)GTP cyclizes to cGMP
C)binding to GAP occurs with very high affinity
D)adenylate cyclase remains active
E)none of the above

Question 5

Which second messenger is produced as a result of nitric oxide binding?

A)cAMP
B)cGMP
C)PIP₂
D)InsP₃
E)DAG

Question 6

In the presynaptic neuron, ______ influx causes neurotransmitter release while in the postsynaptic neuron, ______ enters the cell following opening of ion channels.

A)Na⁺; K⁺
B)K⁺; Na⁺
C)Ca²⁺; K⁺
D)Ca²⁺; Na⁺
E)Na⁺; Ca²⁺

Question 7

What is the primary target of releasing factors from the hypothalamus?

A)thyroid
B)adrenal medulla
C)adrenal cortex
D)posterior pituitary
E)anterior pituitary

Question 8

Amphetamine and mescaline are agonists of ____________, the neurotransmitter often considered a "pleasure agent."

A)serotonin
B) $\gamma$ -aminobutyric acid
C)N-methyl-D-aspartate
D)glutamate
E)dopamine

Question 9

The principle inhibitory neurotransmitter, __________, works by triggering an influx of ______ causing hyperpolarization of nerve cells.

A) $\gamma$ -aminobutyric acid; K⁺
B) $\gamma$ -aminobutyric acid; Cl^-
C)serotonin; K⁺
D)serotonin; Cl^-
E)none of the above

Question 10

A G protein is inactive when the _____ subunit is bound to __________.

A) $\alpha$ ; GMP
B) $\alpha$ ; GDP
C) $\beta$ ; GMP
D) $\beta$ ; GDP
E) $\beta$ / $\gamma$ ; GMP

Question 11

The complex of zinc and cysteine residues seen in the structure of steroid hormone receptors is referred to as a(an)______________ structural motif.

A)zinc loop
B)zinc helix
C)antiparallel zinc sheet
D)zinc finger
E)zinc turn

Question 12

What neurotransmitter is involved with cholinergic synapses?

A)serotonin
B)dopamine
C)acetylcholine
D)glutamate
E) $\gamma$ -aminobutyric acid

Question 13

Glucocorticoids are thought to function as anti-inflammatory agents since they are able to stimulate the synthesis of what protein?

A)tumor necrosis factor (TNF)
B)platelet-derived growth factor (PDGF)
C)transforming growth factor $\beta$ (TGF- $\beta$ )
D)nuclear factor-kappa B (NF- $\kappa$ B)
E)inhibitor-kappa B $\alpha$ (I $\kappa$ B $\alpha$ )

Question 14

Which of the following pathways correctly shows how glycogen synthase is activated in response to the activation of IRS-1 by insulin binding?

A)IRS-1 causes activation of protein kinase B which phosphorylates glycogen synthase kinase thus preventing phosphorylation of glycogen synthase
B)IRS-1 activates a cascade that ultimately phosphorylates ERK which then binds to glycogen synthase
C)IRS-1 activates phosphoinositide 3-kinase and the resulting PIP₃ is an allosteric activator of glycogen synthase
D)IRS-1 activates guanylate cyclase and the resulting cGMP binds to glycogen synthase kinase thus preventing phosphorylation of glycogen synthase
E)none of the above

Question 15

Like G proteins, the Ras protein binds _______ when in its active state which is hydrolyzed to ______ to convert the protein to its inactive state.

A)GTP; GDP
B)GTP; GMP
C)GMP; cGMP
D)cGMP; GMP
E)cGMP; GDP

Question 16

The structures of isoproterenol (left)and epinephrine are shown below. What is isoproterenol?

A)agonist
B)antagonist
C)inverse agonist
D)irreversible agonist
E)non-competitive antagonist

Question 17

When a nerve cell terminates at a muscle cell, the action potential causes opening of _____ channels that results in muscle contraction.

A)Na⁺
B)K⁺
C)Ca²⁺
D)Cl^-
E)none of the above

Question 18

The enkephalins, along with $\beta$ -endorphin, bind to the opioid receptor, so named because the opiate drugs such as __________ bind to it with high affinity

A)morphine
B)fluoxetine (Prozac)
C)phencyclidine
D)methyl phenidylacetate (Ritalin)
E)lysergic acid diethylamide (LSD)

Question 19

Most steroid hormones exert their effects by initial binding to which of the following receptors?

A)receptor in cell membrane
B)receptor in cytosol
C)receptor in nuclear membrane
D)receptor in nucleus
E)none of the above

Question 20

Which of the following hormones binds to a receptor tyrosine kinase?

A)thyroxine
B)epinephrine
C)epidermal growth factor
D)glucagon
E)cortisol

Question 21

Insulin activates glycogen synthase while glucagon inhibits glycogen synthase. Explain the intracellular mechanisms that are used to bring about this activity.

Question 22

Inside a cell, glucagon ultimately results in the phosphorylation of a wide variety of enzymes to control their activity. For each of the following enzymes that is phosphorylated in response to glucagon binding, explain what happens to its activity and why that is important (considering the pathway that the enzyme is in and the overall goal of glucagon).
Acetyl-CoA carboxylase:
Pyruvate kinase:
Glycogen phosphorylase:
Phosphofructokinase-2:

Question 23

Show the reaction of phospholipase C upon PIP₂ and give the names of the products.

Question 24

What amino acid is the source of carbon for the synthesis of ethylene in plants?

A)glycine
B)serine
C)aspartate
D)methionine
E)alanine