Signal Transduction Pathways - Chapter 13

Question 1

What are the key steps to signal-transduction pathways?

Answer 1

1. Release of the primary messenger
2. Reception of the primary messenger; membrane receptors transfer information from the environment to the cell’s interior
3. Relay of information by the second messenger concentration change
4. Activation of effectors that alter the physiological response
5. Termination of the signal

Question 2

What are second messengers? How do they relay information?

Answer 2

Second messengers are small molecules used to relay information from the receptor-ligand complex. Their concentration changes.

They can diffuse to other parts of the cell and influence other processes. They can also amplify the signal in response to a low concentration of signal molecules.

Question 3

What happens if signals are not terminated?

Answer 3

Cells lose their responsiveness to new signals; also increases vulnerability to uncontrolled cell growth and cancer.

Question 4

What does the structure of cyclic AMP or cyclic GMP look like?

Answer 4

Question 5

What structure is this?

Answer 5

Cyclic AMP/Cyclic GMP

Question 6

What structure is this?

Answer 6

Calcium ion

Question 7

What does the structure of calcium look like?

Answer 7

Question 8

What does the structure of inositol 1,4,5-triphosphate (IP3) look like?

Answer 8

Question 9

What structure is this?

Answer 9

Inositol 1, 4, 5-triphosphate (IP3)

Question 10

What structure is this?

Answer 10

Diacylglycerol (DAG)

Question 11

What does the structure of diacylglycerol (DAG) look like?

Answer 11

Question 12

What do Seven-Transmembrane-Helix receptors do in response to ligand binding?

Answer 12

Change conformation and activate G proteins

Question 13

What kind of receptor is the B-adrenergic receptor? What does it bind?

Answer 13

7TM (seven-transmembrane-helix)/G protein complex receptor
Binds epinephrine (adrenaline)

Question 14

Which hormone is responsible for the fight-or-flight response? Which receptor binds it?

Answer 14

Epinephrine and the B-adrenergic receptor

Question 15

Describe the process of ligand binding to 7TM/GPCR receptors.

Answer 15

1. Ligand binds to the receptor
2. Conformational change in the7TM receptor
3. Activation of G proteins

Question 16

What is a G protein?

Answer 16

A GTP-binding protein
When activated, it stimulates adenylate cyclase, which then increases the concentration of cAMP

Question 17

What does adenylate cyclase do? How is it activated?

Answer 17

Adenylate cyclase is an enzyme that increases the concentration of the second messenger cAMP by forming it from ATP. It is stimulated by an activated G protein.

Question 18

Which guanyl nucleotide is bound to the G protein in its unactivated state? Describe its structure.

Answer 18

GDP
G protein exists as a heterotrimer with alpha, beta, and gamma subunits. The alpha subunit binds the nucleotide; the alpha and gamma subunits are anchored to the membrane by covalently attaching fatty acids.

Question 19

What catalyzes the exchange of bound GDP for GTP?

Answer 19

ligand-bound receptor interacts with heterotrimeric G protein and opens the nucleotide bindng site so GDP can leave and GTP can bind; the alpha subunit dissociates from the beta-gamma dimer and transmit signal that receptor has bound its ligand

Question 20

What transmits the signal the 7TM receptor bound its ligand?

Answer 20

Dissociation of the G-protein heterotrimer into G-alpha and G-beta-gamma

Question 21

What does protein kinase A do?

Answer 21

Kinases phosphorylate a substrate at the expense of a molecule of ATP. It mediates the impact of cAMP in eukaryotic cells.

Question 22

Describe the structure of PKA and how it responds to cAMP.

Answer 22

2 regulatory subunits and 2 catalytic subunits

Binding of cAMP to the regulatory subunits releases the catalytic subunits, which are enzymatically active alone. Then, specific serine and threonine residues in targets are phosphorylated.

Question 23

Which residues are phosphorylated by PKA in the presence of cAMP?

Answer 23

serine and threonine

Question 24

What does cAMP phosphodiesterase do?

Answer 24

Turns off the cAMP cascade by converting cAMP into AMP, which cannot activate PKA

Question 25

What converts cAMP to AMP?

Answer 25

cAMP phosphodiesterase

Question 26

How is the signaling pathway started by 7TM receptors turned off?

Answer 26

G-alpha subunits have GPTAse activitiy and can hydrolyze bound GTP to GDP and Pi, deactivating itself.

It acts as a built in clock that resets the G-alpha subunit after a short time period.

Question 27

What influences the likelihood that a receptor will remain unbounded?

Answer 27

concentration of ligand in the environment