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MBOD Week 8 > Signal Transduction II > Flashcards

Signal Transduction II Flashcards

1
Q

What are the three general parts signal general parts of a GPCR?

A
  1. Discriminator receptor (detects signal ligand)
  2. Transducer (exchanges GDP for GTP to become active aka heterotrimeric unit)
  3. amplifier effector ( e.g. adenylate cyclase)
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2
Q

How was it discovered that GTP was necessary for signal transduction in the adenylate cyclase pathway?

A
  • in broken cell preparations adenylate cylclase was inactive even in the presence of the ligand that triggered the response in whole separations
  • they added GTP and the shit worked, so the figured something (the transducer) must be GTP dependent
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3
Q

How many membrane spanning regions are there in GPCR receptors?

A

7 helices

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4
Q

What are the functions of the alpha, beta, and gamma subunits in the heterotrimeric G proteins?

A

alpha - intrinsic GTPase activity and has a lipid modification that holds it in the membrane

beta- doesn’t do a lot

gamma - has a lipid modification that holds it in the membrane

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5
Q

How is a G-protein activated?

A
  • Signal molecule binds to GPCR
  • conformational change is induced in GPCR
  • Conformational change causes the alpha subunit of the G-protein to get rid of GDP and take a GTP
  • After GDP –> GTP exchange the G-protein dissociates from the receptor and the alpha subunit moves away from beta and gamma subunits
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6
Q

What is the rate limiting step G-protein activation?

A

Release of GDP

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7
Q

How do all G-proteins turn off?

A
  1. GTPase activity of the alpha subunit cleaves GTP to GDP causing the alpha unit to dissociate from the protein that its activating
  2. The three subunits (alpha, beta, gamma) combine again which puts them in their inactive state
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8
Q

What families of heterotrimeric proteins activate adenylate cylcase and what subunit is responsible for this action?

A
  • Family I (Gs and Golf)

- alpha subunit is responsible

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9
Q

What family of heterotrimeric proteins activates phospholipase C and what subunit is responsible for this action?

A
  • Family III (Gq)

- alpha subunit

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10
Q

What family of heterotrimeric proteins activates K+ channels and what subunit is responsible for this action?

A
  • Family II (Gi and Go)

- Beta and Gamma subunits

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11
Q

Beta and Gamma subunits open K+ channels when activated, what event terminates this interaction?

A
  • the alpha unit hydrolyzes GTP causing beta and gamma to reassociate with each other leaving them in the inactive state
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12
Q

What is PIP2?

A

Membrane phospholipid with two important components:

  1. DAG (diacylglycerol) that is lodged in the membrane because its the lipid component
  2. IP3 (Inositol 1,4,5-trisphosphate) hydrophilic sugar headgroup on the phospholipid
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13
Q

What cleaves PIP2 into DAG and IP3?

A

Phospholipase C

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14
Q

What signaling pathways involves IP3 and what does IP3 do?

A
  • Gq
  • IP3 interacts with the Ca2+ gate on the ER and floods the cell with Ca2+ which is important in the regulation of several proteins
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15
Q

What are two proteins that are activated by Ca2+ release in the Gq pathway?

A
  • PKC (only partial activation, also needs DAG)

- Calmodulin

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16
Q

Explain the steps in the Gq pathway.

A
  1. Ligand binds to GPCR receptor
  2. alpha unit gets GTP, dissociates, and activates Phospholipase C
  3. Phospholipase C cleaves PIP2 into DAG and IP3
    4a. DAG goes to the membrane to activate PKC
    4b. IP3 goes to the calcium channels to cause Ca2+ release
    5a. Ca2+ binds PKC and PKC becomes completely activated
    5b. Ca2+ activates calmodulin
17
Q

What does calmodulin do?

A
  • Binds to a protein causing it autophosphorylate, which make the protein active
  • Calmodulin interacts with several proteins in this manner which means several cellular processes may be modulated by its activation
18
Q

Do proteins that interact with calmodulin typically retain their activity even after calmodulin has dissociated?

A

Yes, because they will still be phosphorylated for a time, however, they will lose a small amount of activity with calmodulin dissociates.

19
Q

Is calmodulin and enzyme?

A

NOOOOOOOOOOOOOOOOOOOOOOOOO

20
Q

What are IP3, DAG, cAMP, and Ca2+ all examples of?

A

Secondary messengers

21
Q

What does adenylyl cyclase do?

A

converts ATP to cAMP

22
Q

What are some potential problems of having cAMP concentrations that are too high in the cell?

A

It may signal for cell apoptosis

23
Q

What enzyme turns cAMP into adenosine 5’-monophosphate, and what is the significance of this reaction?

A
  • Cyclic AMP phosphodiesterase

- controls the amount of free cAMP in the cell prevents cell apoptosis

24
Q

T or F: Adenylyl cyclase and cyclic AMP phosphodiesterase are heavily regulated due to how critical cAMP levels are in cellular processes

A

True

25
Q

Where is adenylyl cyclase located?

A

in the cell membrane

26
Q

What is PKA and what does is do?

A
  • Protein Kinase A
    1. Protein Kinase A can initiate a phosphorylation cascade that leads to phosphorylation and activation of many proteins
    2. It can enter the nucleus and phosphorylate and thus activate an inactive transcription regulator leading to increased gene transcription
27
Q

Explain the Gs/Golf cascade.

A
  1. Receptor binds to GPCR and the alpha subunit gets a GTP and loses the GDP
  2. Alpha subunit dissociates from beta and gamma and to activate adenylyl cyclase
  3. activated adenylyl cyclase cAMP
  4. cAMP activates PKA
    5a. PKA activates phosphorylase kinase which activates several proteins (e.g. Glycogen phosphorylase)
    5b. PKA can travel to the nucleus and phosphorylate a transcription regulator and genes are transcribed
28
Q

Will PKA phosphorylate the following protein sequence:

Asp-pro-lys-tyr-ser

A

NO, it is specific to serine and threonine residues

MBOD Week 8 (6 decks)

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