#Question id: 1220
#Unit 4. Cell Communication and Cell Signaling
Many G protein-coupled receptors contain seven transmembrane α-helical domains. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would a coupled G protein most likely interact with this receptor?
#Question id: 1221
#Unit 4. Cell Communication and Cell Signaling
If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?
#Question id: 1222
#Unit 4. Cell Communication and Cell Signaling
Particular receptor tyrosine kinases (RTKs) that promote excessive cell division are found at high levels in various cancer cells. HER2 is an RTK that is present at excessively high levels in some breast cancer cells. Herceptin is a protein that binds to HER2 and inhibits cell division. Herceptin may be an effective treatment for breast cancer treatment under which of the following conditions?
#Question id: 1223
#Unit 4. Cell Communication and Cell Signaling
The receptors for steroid hormones are located inside the cell instead of the membrane surface like most other signal receptors. How do steroids gain access to their receptors?
#Question id: 1224
#Unit 4. Cell Communication and Cell Signaling
Put the steps of the process of signal transduction in the order they occur.
1. A conformational change in the signal-receptor complex activates an enzyme.
2. Protein kinases are activated.
3. A signal molecule binds to a receptor.
4. Target proteins are phosphorylated.
5. Second messenger molecules are released.
#Question id: 1225
#Unit 4. Cell Communication and Cell Signaling
The dissociation constant Kd for a receptor-ligand complex is
a. a measure of the affinity of the receptor for the ligand.
b. the concentration of the ligand at which half of the receptors contain bound ligand.
c. a measure of the time it takes for a ligand to be converted to a product.
d. equal to koff/kon