Cell signaling II (Sept. 11 -Simmons)

Question 1

What is PIP(4,5)P2

Answer 1

Phophoinositol bis-phospate. Synthesized from PI, with additional phosphates on 4,5 -OH residues of inositol sugar

Question 2

How is PIP2 (shorthand) attached to the plasma membrane

Answer 2

Attached to the inner leaflet. There are 2 fatty acids embedded in the PM that are attached to the inositol sugar at 1’-OH via a glycerol molecule

Question 3

We learned the Gs and Gi pathways were associated with cAMP. What type of pathways is associated with PIP2 and what is the target enzyme is associated with the GPCR

Answer 3

Gq pathway.

Phospholipase C-beta

Question 4

Phospholipase activates these 2 pathways by cleaving PIP2

Answer 4

• Diacylglycerol -associated with PM ->activates Protein Kinase C
• Inositol tri-phosphate (IP3) -> free floating which releases Ca2+ from ER

Question 5

How is Ca2+ conc. maintained so low in cytosol?

Answer 5

There are Na+ driven anti porters in PM as well as ca2+ active energy pumps to move calcium out of cell.
In addition, There are Ca2+ binding proteins in cell, pumps that move calcium into ER, and pumps into mitochondria (using an H+ gradient)

Question 6

True or false - higher levels of a drug which activates Gq pathway cause higher levels of Ca2+ oscillation in cells

Answer 6

False. Frequency of the spike oscillation increases - not the amplitude

Question 7

Ca2+ movement is described as waves. This is due to the spread of _____ moving across an area inducing ______ nearby

Answer 7

1. Calcium

2. channels

Question 8

Describe the structure of calmodulin

Answer 8

• Shaped like a dumbbell (globular portion at each end connected by flexible helix)
• Can bind up to 4 Ca2+ ions (2 each head)

Question 9

What is the function of calmodulin?

Answer 9

If at least 2 Ca2+ bind -> cause the calmodulin to bind to target proteins and affects their activity

Question 10

Describe the mechanism of calmodulin binding to CaM kinase II

Answer 10

Calmodulin binds calcium and acrobats it to allow it to bind to inactive target kinase at the inhibitory domain. Autophosphorylation occurs to fully activate the kinase. Remains active even when calcium levels have dropped and calmodulin has dissociated (as long as activation phosphate remains bound)

Question 11

True or False. All PKCs require diacylglycerol and Ca2+ for activation.

Answer 11

False. Out of 11 PKC, 4 of them explicitly require Ca2+ to become fully active

Question 12

How are Ca2+ oscillations recognized by a cell?

Answer 12

Sufficient number of Ca2+ oscillations increase the activity of the CAM kinase to a maximum level of activity. The body can recognize these levels of activations…becomes accustomed and allows lower level of calcium to maintain a high level of activity of CAM kinases.

Question 13

List the function of these 3 molecules and the mechanism of what they affect briefly (the kinase)

1. cAMP
2. cGMP
3. Ca2+

Answer 13

1. Protein Kinase A
2. Protein Kinase G
3. Protein Kinase C, CaM Kinase-II, myosin light chain kinase, phosphorylase kinase

Question 14

How many families of adrenergic receptors are there? And what pathway does each affect.

Answer 14

9 families, a1a, a2b, b1, b2, etc.
Gq - a1 family
Gi/Go - a2 family
Gs - beta family

Notable exceptions: Beta 3 activates all 3 pathways

Question 15

What are the Gs, Gi, Go, and Gq pathways usually responsible for

Answer 15

Gs - stim. cAMP -> vasodilation, lipolysis, increased heart rate
Gi - inhib. cAMP -> vasoconstriction, increased epinephrine > norepinephrine
G0 - k+ and phospholipase C -> same effects as Gi?
Gq - phospholipase C -> vasoconstriction, cardiac growth

Question 16

Know the general features of agonist, antagonist, and endogenous molecules

Answer 16

Agonist - only affects one family of receptor

Antagonist - selective blocks the binding of endogenous molecules from activating a particular family of receptors

Question 17

How does NO work to cause vasodilation?

Answer 17

No -> activates guanylyl cyclades -> increases cGMP -> increases PKG activity -> relaxation

Question 18

How is calmodulin involved in NO production?

Answer 18

Activated calmodulin is involved creation of NO from L-arginine and L-citrulline…using NADPH as a reduction molecule.
ACTIVATION of NOS (nitrous oxide synthetase)

Question 19

Bradykinin acts to cause vasodilation. Describe the binding of this molecule and the signal transduction.

Answer 19

• Bradykinin binds to GPCR (Gq)
• Phospholipase C activated and cleaves to form IP3 and DAG
• Increase in Ca2+
• Calmodulin activates and causes activation of NOS
• NO gas is soluble and moves into smooth muscle cells
• Binds to Guanylyl cyclases
• Increase in cGMP created from GTP
• Increase in PKG

Question 20

How is the previous pathway altered when using pharmacological agents: nitrovsodilators?

Answer 20

Bypass endothelial pathway. Direct affect on NO and NOS production.