G proteins play an important role in many biological signaling pathways. A well-known example is G protein mediated sign

[answerhappygod]

G Proteins Play An Important Role In Many Biological Signaling Pathways A Well Known Example Is G Protein Mediated Sign 1 (234.37 KiB) Viewed 54 times

G proteins play an important role in many biological signaling pathways. A well-known example is G protein mediated signaling in heart muscle cells stimulated by binding of adrenaline to a G protein coupled receptor (GPCR). G proteins (so-called because they can bind the guanine nucleotides GDP and GTP) consist of three different subunits (GQ, G3 and G). When a GPCR is activated (leading to a rate kact > 0), it exchanges GDP bound to Gaby to GTP. GTP:Gaß, immediately splits into GTP:G, and Gey. GTP:Ga can be inactivated again by hydrolysis of the bound GTP to GDP and inorganic phosphate (P;). Inactivated GDP:GQ can bind Gs, again to form the inactive heterotrimeric G protein complex GDP:Gapr. The activation cycle of the heterotrimeric G proteins can be described by the following biochemical reactions: khy GDP:GQpx + GTP kact GTP:GQ +Gigy+GDP GTP:G GDP:Ga + P GDP:Ga +Gsm kar GDP:Gaby The parameter values are kact = 0.1s-1, khy = 0.115-1 and ks = 15-1. These values refer to molecular numbers, so in the lecture material e.g. kny would be called kwy. Initially GDP:Gaby(0) = GTP(0) = 105 molecules are present, all other species are absent at time t = 0. a) Use the information from the text above to describe the biochemical meaning of each reaction. b) Write down the ODEs for the number of molecules of all species. Hint: Since there is no standard notation in the systems biology community, you should always define your variables at the start. E.g. you could write GTP to denote the number of molecules of GTP. c) Implement the ODEs in MATLAB and numerically solve them for t€ (0,30]s with ode15s. Plot the molecular numbers of GDP:Gaby, GTP:Ga and GDP over time using a logarithmic time-axis. Describe your observations. Hint: Look up semilogy in the MATLAB documentation. d) Simulate the same system again and compare the run times between the ode45 and ode15s ODE solvers. Which ODE solver is faster for this system and why? Hint: Look up tic and toc in the MATLAB documentation. You can refer to this link for further information on the two ODE solvers: