Question

Which of the following correctly states an essential step in the function of heterotrimeric G protein function?

a) Activation by GTP binding
b) Release of GDP
c) Interaction with G protein-coupled receptors
d) Effector enzyme activation

Answer 1

An essential step in the function of heterotrimeric G proteins is their interaction with G protein-coupled receptors, initiating a sequence of GDP-GTP exchange, subunit dissociation, upstream signaling, and finally, GTP hydrolysis to terminate the signal.

Step-by-step explanation:

The function of heterotrimeric G proteins is a vital part of cell signaling mechanisms. Among the options presented, interaction with G protein-coupled receptors is an essential step in the function of heterotrimeric G proteins. This interaction is a multi-step process involving several critical events:

1. A signaling molecule binds to a G protein-coupled receptor (GPCR) on the cell's surface.
2. This binding prompts the exchange of GDP for GTP on the α subunit of the G protein - an event signifying the activation of the G protein.
3. The activated α subunit dissociates from the β and γ subunits, allowing both parts to interact with various effector molecules within the cell.
4. Ultimately, hydrolysis of GTP to GDP on the α subunit serves to switch off the signal, reassociating the subunits and returning the G protein to its inactive state.

This cycle enables cells to respond to a multitude of signals, including hormones, neurotransmitters, and sensory stimuli, initiating a range of cellular responses like activation of enzymes, opening of ion channels, and changes in cell function.