Chapter 13: Signal Transduction Pathways

Question 1

Most signal molecules:

Answer 1

bind to membrane receptors and transmit information across a membrane without traversing the membrane.

Question 2

Examples of second messengers include:

Answer 2

1. cAMP
2. Calcium ion
3. Diacyl Glycerol

Question 3

Advantages of second messengers include that:

Answer 3

1. the signal can be amplified by making many second messengers.
2. second messengers can freely diffuse to other sites within the cell.
3. a few common second messengers can be used in multiple signaling pathways.

Question 4

Which of the following amino acids can be phosphorylated?

Answer 4

tyrosine, serine, threonine

Question 5

Which form of the guanyl nucleotide is bound in the unactivated state?

Answer 5

GDP

Question 6

The mechanism by which insulin-signaling processes might be terminated include:

Answer 6

Protein dephosphorylation by phosphatases.

Question 7

How does the binding of a hormone to receptor activate a G-protein?

Answer 7

It causes an exchange of GTP for bound GDP.

Question 8

Example(s) of disease(s) caused by altered G-protein activity include:

Answer 8

whooping cough and cholera

Question 9

When insulin binds to its receptor, which of the following occurs?

Answer 9

A PIP2-dependent kinase is activated.

Question 10

Define: Primary Messenger

Answer 10

Message received by the cell

Question 11

Define: Second Messenger

Answer 11

Intracellular chemical that relays message from ligand receptor complex

Question 12

Define: G-Protein coupled receptor

Answer 12

Composed of seven transmembrane helices

Question 13

Define: Heterotrimeric G-Protein

Answer 13

Activated by 7TM Receptor

Question 14

Define: G(as)

Answer 14

Activates adenylate cyclase

Question 15

Define: Protein kinase A

Answer 15

Stimulated by cAMP

Question 16

Define: cAMP Phosphodiesterase

Answer 16

Results in the inactivation of protein kinase A

Question 17

Define: GTPase activity

Answer 17

Results in the reassociation of G(alpha) and G(beta theta).

Question 18

Define: Cholera

Answer 18

Due to persistent stimulation of G(as)

Question 19

Define: Pertussis

Answer 19

Results from G(as) inhibition

Question 20

Define: Phospholipase C

Answer 20

Generates two second messengers

Question 21

Define: G(aq)

Answer 21

Activates phospholipase C

Question 22

Define: Inositol Trisphosphate

Answer 22

Activates Ca2+ channel

Question 23

Define: Protein Kinase C

Answer 23

Activated by diacylglycerol

Question 24

What are the three major classes of membrane receptors?

Answer 24

1. G-Protein coupled Receptors
2. Receptors that dimerize on ligand binding and recruit tyrosine kinases
3. Receptors that dimerize on ligand binding that are tyrosine kinases

Question 25

Explain how a small number of hormones binding to the extracellular surface of a cell can have a large biochemical effect inside the cell.

Answer 25

The initial signal, the binding of the hormone by a receptor, is amplified by enzymes and channels.

Question 26

What are some of the structural features common to all membrane-bound receptors?

Answer 26

The receptor must have a site on the extracellular side of the membrane to which the signal molecule can bind and must have an intracellular domain. Binding of the signal to the receptor must induce structural changes on the intracellular domain so that the signal can be transmitted.

Question 27

Why is the GTPase activity of G proteins crucial to the proper functioning of a cell?

Answer 27

The GTPase activity terminates the signal. Without such acitivity, after a pathway has been activated, it remains activated and is unresponsive to changes in the initial signal.

Question 28

In an experiment on the nature of receptor tyrosine kinase signaling, a gene was synthesized that encoded a chimeric receptor - the extracellular part came from the insulin receptor, and the membrane-spanning and cytoplasmic parts came from the EGF receptor. The striking result was that the binding of insulin induced tyrosine kinase activity, as evidenced by rapid autophosphorylation.

What does this result tell you about the signaling mechanisms of the EGF and insulin receptors?

Answer 28

The insulin receptor and the EGF receptor employ a common mechanism of signal transmission across the plasma membrane.

Question 29

A mutated form of the alpha-sub-unit of the heterotrimeric G protein has been identified; this form readily exchanges GDP for GTP even in the absence of an activated receptor.

What would be the effect on signaling pathway containing the mutated alpha-sub-unit.

Answer 29

The mutated alpha-sub-unit would always be in the GTP form and, hence, in the active form, which would stimulate its signaling pathway.

Question 30

Glucose is mobilized for ATP generation in muscle in response to epinephrine, which activates G(as). Cyclic AMP phosphodiesterase is an enzyme that converts cAMP into AMP.

How would inhibitors of cAMP phosphodiesterase affect glucose mobilization in muscle?

Answer 30

G(as) stimulates adenylate cyclase, leading to the generation of cAMP. This signal then leads to glucose mobilization. If cAMP phosphodiesterase were inhibited, then cAMP levels would remain high even after the termination of the epinephrine signal, and glucose mobilization would continue.