Question

Consider the events involved in the stimulation of heart muscle. Arrange the events in the stimulation of heart muscle in sequence. Note that this question does not list every step in the pathway, but the steps presented should be arranged in order.

1. Conversion of ATP into cyclic AMP
2. Activation of G-proteins
3. Phosphorylation of proteins that induce contraction in muscle cells
4. Activation of protein kinase A
5. Activation of adenylyl cyclase

Answer 1

2,5,1,4,3

Step-by-step explanation:

• Activation of trimeric G protein starts when primary messenger binds with 7 transmembrane protein and activate it
• There are three types of trimeric G protein: GS,GI and Gq
• Activated 7 transmembrane acts as guanosine nucleotide exchange factor (GEF) and replace GDP from GTP of trimeric G protein
• Activated GS protein dissociate into two components called GS
  `\alpha` GTP and Gβγ
• GS
  `\alpha` GTP moves along with membrane and binds with effector enzyme called adenylyl cyclase (activation)
• Activated adenylyl cyclase catalyse synthesis of a potent secondary messenger called cAMP (cyclic adenosine monophosphate)
• High level of cAMP activates a protein called protein kinase A (pKA) which phosphorylates phosphorylase kinase (pK) and activates it
• On the other hand at the same time pKA phosphorylates glycogen synthase (GS) and inactivate it
• Phosphorylase kinase becomes active and phosphorylates glycogen phosphorylase and makes it active, glycogen phosphorylase catalyse breakdown of glycogen (in liver and muscle cells)