Lac repressor binds as a tetramer to two operators.

TLS Online TPP Program

#Id: 1376

#Unit 4. Cell Communication and Cell Signaling

Two mechanisms for terminating cytokine signal transduction

1.  Short-term regulation

2.  Long-term regulation

TLS Online TPP Program

#Id: 1377

#Unit 4. Cell Communication and Cell Signaling

Short-term regulation: 

JAK2 deactivation by SHP1 phosphatase

TLS Online TPP Program

#Id: 1378

#Unit 4. Cell Communication and Cell Signaling

Long-term regulation: 

• SOCS proteins

• Targets the receptor as well as JAK2 for degradation by the ubiquitin-proteasome pathway

TLS Online TPP Program

#Id: 1379

#Unit 4. Cell Communication and Cell Signaling

The rate-limiting step in actin filament assembly is the formation of a short actin oligomer (nucleus).

TLS Online TPP Program

#Id: 1380

#Unit 4. Cell Communication and Cell Signaling

The critical concentration (Cc) is the concentration of free G-actin at which the filaments are formed.

TLS Online TPP Program

#Id: 1381

#Unit 4. Cell Communication and Cell Signaling

At steady state, ATP–G-actin subunits add preferentially to the (+) end, while ADP–G-actin subunits disassemble from the (−) end, giving rise to treadmilling of subunits.