Difference Between Internal Receptors and Cell Surface Receptors

The key difference between internal receptors and cell surface receptors is that internal receptors are present in the cytoplasm and respond to hydrophobic ligands that enter the cell across the plasma membrane while cell surface receptors are present on the cell membrane and respond to external ligands that do not travel across the cell membrane.

Cell signalling is an important process in multicellular organisms. Cells release signalling molecules known as ligands. They are small, volatile or soluble molecules which can bind with receptors. Receptors mediate the signal transduction for cellular responses. Receptors are proteins that are mainly located on the surface or in the cytoplasm. A ligand binds only with a specific receptor. Receptors can be cell surface receptors or internal receptors (intracellular receptors).

CONTENTS

1. Overview and Key Difference
2. What are Internal Receptors 
3. What are Cell Surface Receptors
4. Similarities Between Internal Receptors and Cell Surface Receptors
5. Side by Side Comparison – Internal Receptors vs Cell Surface Receptors in Tabular Form
6. Summary

What are Internal Receptors?

Internal receptors or intracellular receptors are the receptor proteins found inside the cell in the cytoplasm. These receptors respond to the ligands that enter the cell through the cell membrane. When the ligand binds with the intracellular receptor, it undergoes a conformational change. Gene expression is one of the most important processes occurring in a cell. Intracellular receptor-ligand complexes travel to nucleus and transmit signals necessary for gene expression and its regulation. Thus, internal receptors can directly influence gene expression in cells without the involvement of secondary messengers.

In addition to the above, hormones of the cell use intracellular receptors. Furthermore, nuclear receptors are also present in the cell nucleus. Apart from them, endoplasmic reticulum also utilizes intracellular receptors.

What are Cell Surface Receptors?

Cell surface receptors are transmembrane proteins anchored with the cell membrane. These receptors bind to the external ligands that do not cross the cell membrane and enter the cell. Specifically, these receptors convert extracellular signals into intracellular signals. Most importantly, cell surface receptors are specific to individual cell types.

There are three types of cell surface receptors as ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors. These receptors carry out most of the cell signalling in multicellular organisms.

What are the Similarities Between Internal Receptors and Cell Surface Receptors?

• Internal receptors and cell surface receptors are the two main types of cell receptors.
• Both are able to bind with signalling molecules or ligands.
• They are involved in signal transduction.
• In fact, both internal receptors and cell surface receptors participate in most signalling pathways.
• Moreover, they are proteins.

What is the Difference Between Internal Receptors and Cell Surface Receptors?

Internal receptors are the receptors present in the cytoplasm. In contrast, cell surface receptors are the receptors present on the cell membrane. So, this is the key difference between internal receptors and cell surface receptors. Moreover, a further difference between internal receptors and cell surface receptors is that the internal receptors bind with the ligands that enter the cell while cell surface receptors bind with the external ligands.

The below infographic summarizes the difference between internal receptors and cell surface receptors.

Summary – Internal Receptors vs Cell Surface Receptors

Internal receptors and intracellular receptors are the two main types of receptors that mediate signal transduction in cells. Internal receptors are inside the cytoplasm and bind with the hydrophobic ligands that enter the cell across the cell membrane. In contrast, cell surface receptors are present on the cell membrane, and they bind with the external ligands that are outside the cell membrane. So, this is the summary of the difference between internal receptors and cell surface receptors.

Reference:

1. “Signaling Molecules and Cellular Receptors.” Biology for Majors I, Lumen Learning, Available here.

Image Courtesy:

1. “Figure 09 01 03” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Receptor (Biochemistry)” By Wyatt Pyzynski – Own work (CC BY-SA 4.0) via Commons Wikimedia