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Wize University Biology Textbook > Cell Communication

Types of Cell Receptors [Internal Receptors, GPCRs, RTKs, Ion Channels]

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Internal Receptors

Signal detection usually occurs through internal receptors or surface receptors (more common). Receptors are proteins located inside or on the cell surface which bind to the signaling molecule and transmit the signal to the cell's interior. There are several different types of cell receptors.

Internal Receptors

  • Located on the cell's cytoplasm.
  • Respond to hydrophobic ligands. Example: certain hormones in the human body.
  • Often the receptor-ligand complex moves into the nucleus to regulate gene expression.

Photo by OpenStax College / CC BY



The following are cell-surface receptors. Remember that these are integral (transmembrane) proteins anchored on the cell's lipid bilayer. They perform signal transduction, or the relaying of information from the cell's exterior to the interior.


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G-Protein Coupled Receptors (GPCRs)

The following are cell-surface receptors. Remember that these are integral (transmembrane) proteins anchored on the cell's lipid bilayer. They perform signal transduction, or the relaying of information from the cell's exterior to the interior.

GPCRs are a type of receptor which interacts with G proteins. Humans have over 1000 different types of GPCRs and they carry out a very wide array of functions in our cells.
  • A G protein is attached to the intracellular side of the membrane.
  • They have three subunits: the alpha, beta, and gamma subunits.
  • G proteins have the ability to bind GTP and GDP.
  • The variety of GPCRs comes from the variety of molecules they activate.

Photo by Repapetilto / CC BY

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General GPCR pathway:

  1. Before the ligand binds, the G-protein is associated with its subunits, holding a GDP.
  2. The signal molecule binds to the cell surface receptor.
  3. Upon binding, the receptor undergoes a conformational change that activates the G-protein.
  4. The G protein's alpha subunit then lets go of GDP and picks up GTP and is now active.
  5. The G protein then dissociates from the GPCR and into alpha and beta-gamma subunits.
  6. These subunits can go activate other proteins as a result.
  7. Eventually the GTP is hydrolyzed to GDP.
  8. The subunits re-associate and the cycle starts again.
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Receptor Tyrosine Kinases (RTKs)

RTKs are transmembrane proteins which receive signals from the extracellular environment, and act as an enzymes.
  • On the extracellular side, RTKs have the receptor domain, and the enzyme domain is located on the intracellular side of the membrane.
  • The enzymatic domain contains a tyrosine residue and acts as a kinase. Kinases are enzymes which transfer phosphate groups - a type of reaction which is called a phosphorylation reaction. RTKs act in dimers (pairs).
  • Upon binding of the ligand (the signaling molecule), the RTK undergoes a conformational change, causing two RTKs to come together and form dimers.
  • Once together, each RTK in the dimer phosphorylates the tyrosines on the other RTK. This is called cross phosphorylation.
  • Once phosphorylated, the enzymatic domain acts as a docking platform for other proteins involved in signal transduction.


Photo by BQUB17-JRamon / CC BY

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Ion Channels Receptors

Ion receptor channels are ion channels that open and close upon binding of a signaling molecule.
  • Upon binding of the ligand (signaling molecule), it causes the channel to open.
  • This allows for the flow of ions (e.g. K+, Na+, Ca+, Cl-) from an area of high concentration to an are of low concentration.

Photo by OpenStax / CC BY

Practice: What Type of Receptor?

A certain hormone finds its receptor on a particular cell. When it binds, the receptor opens, allowing Ca2+ to rush into the cell. This receptor must be:

Practice: GPCRs

What is true about GPCRs?

Practice: Receptor Tyrosine Kinases (RTKs)

Which is true about receptor tyrosine kinases (RTKs)?
Extra Practice
Order the G protein coupled receptor signalling mechanism in order of events:
Order the G protein coupled receptor signalling mechanism in order of events:
Order the G protein coupled receptor signalling mechanism in order of events:
Practice: Signal
Think about the GPCR pathway that was discussed in class. It went Signal molecule -> GPCR -> G protein -> adneylyl cyclase -> cAMP -> downstream effects. Which of the following was the secondary messenger?
what is true about cell membrane receptors?
Practice: G-Protein Coupled Receptors
Match the G-protein coupled receptor pathway component to the general signal transduction role.
What is one of the most common changes in the cell after receiving a ligand that activates the adenylyl cyclase pathway or the tyrosine kinase pathway?
Order the G protein coupled receptor signalling mechanism in order of events:
Practice: Signal
Think about the GPCR pathway that was discussed in class. It went Signal molecule -> GPCR -> G protein -> adneylyl cyclase -> cAMP -> downstream effects. Which of the following was the secondary messenger?
A certain ligand is known to be able to bind to multiple cell surface receptors. However, once it binds to any one of its receptors, it requires a lot of energy to dissociate the ligand from the receptor. What can you say about this ligand?
Practice: G-Protein Coupled Receptors
Match the G-protein coupled receptor pathway component to the general signal transduction role.
What activates a G protein
For the following odour signalling scenario, describe the signal relay pathway by answer the following questions:
1. What type of receptor is this?
2. What is the ligand?
Order the G protein coupled receptor signalling mechanism in order of events:
What type of molecules are membrane transporters (eg. pumps, channels, carriers)?
Which of the following would result in a permanently active response?
Consider the following scenario for this 4 part question:
Which of the following process(es) require phosphorylation as a chemical modification to activate a protein? Select all that apply.
Consider the following scenario for this 3 part question:
Receptor tyrosine kinases (RTKs) are abundant class of protein receptors in human cells. Which of the following would be true when comparing different RTKs from a single human sample?
They would contain only synonymous mutations
They would have the same amino acid sequence
There are multiple different types of G-protein coupled receptors (GPCRs) in the human body. Which of the following statements are correct regarding these proteins?
A high global alignment of amino acid sequences
Binding of the same ligand
Insulin is a hormone that acts as a signal to tell the cell to take up glucose from the blood. There is a protein associated with the cell membrane that sends a signal to the cell once it binds to insulin. What kind of membrane protein is this?