Question

2. Here is the figure of the G protein couple receptor (GPCR) activation of K+ channels in the pacemaker cells of the heart (right).

Under which of the following scenarios would the effect of acetylcholine be enhanced (thus resulting in slowing the heart beat rate)? For those scenarios which do not enhance the effect of acetylcholine, explain why it would not do so. (3 pts)

a. Changes in the protein structure of the K⁺ channel which would decrease the interaction of the activated bg complex and the K⁺ channel.

b. An extremely high affinity of the G protein for GDP.

c. GTP molecules which are not hydrolysable

d. Changes in the receptor protein which decreases the affinity of the receptor for acetylcholine

3. Compare and contrast cell signaling via GTP-binding proteins (molecular switches) and signaling through the cortisol activation of a transcription factor (4 pts).

4. Many extracelluar signals which promote survival and growth work through RTKs. The activated AKt (also called protein kinase B) promotes cells survival through its interaction with Bad and Bcl2. Akt is able to phosphorylate Bad which inactivates it (thus it no longer will promote cell suicide).

Which of the following scenarios are false? If they are false explain why they are false.

a. When Akt is activated, its major function is to phosphorylate other proteins

b. When there are signals for cell death, Akt will be phosphorylated:

c. When Akt is activated, it will inhibit Bcl2:

d. Akt is activated when it is phosphorylated.

Answer 1

2) pacemaker cells found in sinoartrial node (SA node) . This cardiac muscles cells have G protein coupled receptor , when acetylcholine bound to these receptors, G1 beta gamma complex become active , which bind to K+ ion channel on the membrane , open it and K+ flows in. Influx of K+ ion causes slow heart rate. Further, alpha subunit of G protein hydrolyze GTP , signal is terminated , K+ channel closes and G protein return to its inactive state.

C) GTP molecule which are not hydrolysable are the scenerio in which effect of acetylcholine enhanced because G protein activate in the presence of GTP a d open K+ channel.

Scenerio a is not enhanced the effect of acetylcholine because no interaction between beta gamma and K+ channel lead to decrease the effect of acetylcholine means increase heart rate, scenerio b also not enhanced because high affinity of G protein toward GDP terminate signal of acetylcholine., Scenerio d is also not enhanced the effect of acetylcholine because this scenerio decrease the affinity of acetylcholine toward receptor.

4) protein kinase B or Akt is a ser/ thr kinase that play role in multiple cellular processes such as cell proliferation , apoptosis etc. Akt is activated by phosphorylation by its activating kinase. BAD and BCl-2 are proapoptotic protein of BCl -2 family. Akt phosphorylate BAD which make BAD dissociate from Bcl2/BCl-X complex and loss the proapoptotic function.

Here, option a is true, once Akt activate, it phosphorylate other protein.

b) this scenerio is false because Akt activate by phosphorylation during cell survival signal not in cell death signal.

c) scenerio is true, activated Akt inactivate proapoptotic signal BCl- 2

d) it is also true Akt activated by phosphorylation