Question

What is the major functional difference between GPCRs and RTKs?

GPCRs have more transmembrane domains then RTKs.

GPCRs are integral membrane proteins and RTKs are not.

RTKs are enzymes (tyrosine kinases) and GPCRs are not.

RTKs can activate the Ras-MAP kinase pathway and GPCRs cannot.

GPCRs are a larger superfamily of receptors than RTKs.

Answer 1

Answer: Please refer the table (below) for major difference between GPRs and RTKs .

1. GPCRs have more transmembrane domains then RTKs.

This statement is correct. GPCRs has seven-transmembrane domain. RTKs are dimer.

2. GPCRs are integral membrane proteins and RTKs are not.

This statement is incorrect. Moreover, GPCRs and RTKs are transmembrane (integral) proteins.

3. RTKs are enzymes (tyrosine kinases) and GPCRs are not.

This statement is correct. RTKs are enzymes (tyrosine kinases) and GPCRs are not.

4. RTKs can activate the Ras-MAP kinase pathway and GPCRs cannot.

This statement is incorrect. Mitogen-activated protein kinase (MAPK) can be activated by a variety of extracellular stimuli, including those mediated by receptor tyrosine kinases (RTKs) and G-protein-coupled receptors (GPCRs). MAPK activation pathway starts with the activation of Ras (a small G protein anchored to the plasma membrane). In its inactive state, Ras is bound to GDP. However, when SH2-containing proteins join with activated RTKs, they cause Ras to bind GTP in place of GDP and become active. Then the GTP-bound Ras (which is not itself a kinase) activates the serine-threonine kinase in the MAP kinase cascade. Ultimately, it’s activated by RTKs but coupled with G proteins.

5. GPCRs are a larger superfamily of receptors than RTKs.

This statement is correct.

Explanation

GPCRs Vs RTKs
Characteristics	GPCRs	RTKs
Definition	A type of cell surface receptors that have seven transmembrane domains.	A type of enzyme-linked cell surface receptors that have two monomers.
Structure	Seven transmembrane domains.	It is a dimer
From a single ligand binding	Trigger only one cell response	Triggers multiple cell response
Energy molecule involved	GTP	ATP
Linked enzyme	No	Enzyme kinases

GPCRs - G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that share a common structure and method of signaling. The members of the GPCR family all have seven seven-transmembrane domain receptors that cross the membrane, and they transmit signals inside the cell through a type of protein called a G protein. The inactive form of the G protein transforms into the active form by converting GTP into GDP and utilizing the released energy.

RTKs - Receptor tyrosine kinases are a type of receptor proteins that involve with most of the cell signaling pathways. They are kinase enzymes. Kinase catalyzes the transfer of phosphate groups to a substrate. These receptors contain tyrosine kinases that transfer a phosphate group from ATP to tyrosine. Receptor tyrosine kinase has two similar monomers. Once a signaling molecule binds with the receptor, it forms a dimer. Then, kinases phosphorylate ATP and add phosphate groups to each of the six tyrosines. Hence, dimer becomes phosphorylated, which is a fully activated tyrosine kinase. Activated tyrosine kinase sends signals to other molecules of the cell and mediates signal transmission. The most important characteristic of receptor tyrosine kinase is, it can activate multiple signaling pathways and when it activates, it can create multiple cell responses at once.