G protein-coupled receptors are found only in eukaryotes. The ligands that bind to G protein-coupled receptors include a range of compounds including pheromones, hormones and neurotransmitters and range in size all the way from small peptides to large proteins.

Which of the following best describes the function of the G protein?

Question

G protein-coupled receptors are found only in eukaryotes. The ligands that bind to G protein-coupled receptors include a range of compounds including pheromones, hormones and neurotransmitters and range in size all the way from small peptides to large proteins.

Which of the following best describes the function of the G protein?

BlackTom AI · Accepted Answer

To tackle this question, I’ll evaluate what each option says about how G proteins function in GPCR signaling. 
Option 1 states that once the ligand binds the receptor, the active G protein binds to its enzyme and this causes GDP to be replaced by GTP. The issue here is the sequence: the exchange of GDP for GTP on the G protein is what activates it, and this exchange is what enables the G protein to interact with its effector. Simply stating that binding to the enzyme causes GDP to be replaced omits the critical regulatory event (GDP→GTP exchange) that activates the G protein. 
Option 2 claims that ligand binding to the receptor causes GDP to replace with GTP on the G protein. This aligns with the classic model: receptor activation promotes GDP-GTP exchange on the G protein, producing the active GTP-bound form that can then interact with and regulate its effector enzyme, initiating the next step in the signaling cascade. The description mirrors the essential activation mechanism of heterotrimeric G proteins. 
Option 3 says the binding of GDP activates the G protein, which is logically inconsistent because GDP-bound G proteins are inactive; activation requires GTP binding. This makes the statement internally contradictory and biologically incorrect. 
Option 4 describes the G protein as a membrane receptor and asserts that ligand binding leads to GDP↔GTP exchange, activating the G protein to bind its enzyme. This confuses the roles: G proteins themselves are not membrane receptors; GPCRs are the receptors. The G protein acts as a molecular switch that is activated by GTP, not by being a receptor itself. The misassignment of receptor function to G proteins renders this option invalid. 
Putting these pieces together, the most accurate description among the choices is Option 2, which correctly identifies GDP-GTP exchange as the activation step that enables the G protein to interact with its target enzyme and propagate the signal. The other options either mishandle the order of events, confuse the roles of receptor and G protein, or claim activation occurs with GDP rather than GTP, all of which contradict established GPCR signaling mechanisms.

类似问题

Which ONE of the following statements about metabotropic receptor signalling is CORRECT?

Question at position 30 When a ligand binds to this type of receptor, a G protein is released for activation of downstream signaling cascades.Metabotropic receptorIonotropic receptorVoltage-gated receptorMechanically-gated receptorClear my selection

Question at position 43 The role of G proteins in neurotransmitter signaling is to:Activate adenylate cyclase, producing cAMPDirectly bind to and open ion channelsDiffuse across the membrane and bind to intracellular enzymes Inhibit ligand-gated ion channels

Which of the following is a regulatory protein associated with second messenger systems?

You own a bond that pays $64 in interest annually. The face value is $1,000 and the current market price is $1,021.61. The bond matures in 11 years. What is the yield to maturity?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单