Catch up

What does a target cell require to respond to an extracellular signal molecule?

• Access to the signal molecule

• The presence of an appropriate receptor for the signal molecule

• Appropriate intracellular signaling pathways

• All of the above

A target cell can respond quickly to an extracellular signal if:

• the cell does not require a receptor for the signal molecule

• the response does not require target cell proteins to be altered.

• the response does not require new gene transcription or new protein synthesis.

• The signal is contact dependent

Most extracellular signal molecules act on cell-surface rather than intracellular receptors because they are:

• too large to pass directly across the plasma membrane.

• too hydrophilic to pass directly across the plasma membrane.

• either too large, too hydrophilic, or both to pass directly across the plasma membrane.

Which G protein component or components have GTPase activity?

• alpha subunit

• beta subunit

• gamma subunit

• alpha/beta complex

Which component or components of a G protein can, on its own, activate downstream proteins in an intracellular signaling pathway?

• alpha subunit

• beta subunit

• beta/gamma complex

• Alpha subunit and beta/gamma complex

Which of the following is not a small intracellular signaling molecule (second messenger)?

• Cyclic AMP

• Phospholipase C

• Inositol triphosphate

• Diacylglycerol

When activated by a GPCR, adenylyl cyclase

• converts AMP to cAMP.

• converts ADP to cAMP

• converts ATP to cAMP

• converts cyclic AMP to AMP

When activated phospholipase C chops the head off an inositol phospholipid, it produces two small signaling molecules that relay the signal onward. Which of these stays in the plasma membrane?

• Inositol 1,4,5-trisphosphate (IP3)

• Diacylglycerol (DAG)

How does IP3 function in the inositol phospholipid pathway?

• It binds to and opens Ca2+ channels that are embedded in the ER membrane, releasing Ca2+into the cytosol.

• It directly activates protein kinase C.

• It activates phospholipase C.

Following the binding of an extracellular signal molecule, receptor tyrosine kinases (RTKs) are activated by dimerization, which allows:

• each polypeptide chain in the dimer to phosphorylate itself on specific tyrosines in its cytoplasmic tail

• each polypeptide chain to cross-phosphorylate the other chain in the dimer on specific tyrosines in its cytoplasmic tail.

• the receptor to be internalized so that it can phosphorylate and activate various intracellular signaling proteins