Learn. Apply. Retain.

With Modern Biology, your students at any level of biology study can learn how cell surface receptors work, apply that knowledge in a Modern Biology experiment, and retain their understanding far beyond passing the test. In this article, we’ll discuss how you can integrate the easy, economical hands-on experience of a Modern Biology experiment into your curriculum for cell surface receptors.

The Essential Elements of Understanding Cell Surface Receptors

No matter what your mandated curriculum, you will be teaching your students the same basic facts about cell surface receptors, also known as transmembrane receptors:

• Cell surface receptors are proteins. They are anchored in the cell membrane, where they bind to external ligands. Most ligands are also proteins.
• Ligands do not have to enter the cell to affect it. They act as an external signal to accomplish an internal change in the cell.
• Cell surface receptor proteins are basic to the normal function of the cell. Errors in the structure of receptor molecules have been shown to play a role in asthma, cancer, hypertension, and cardiovascular disease.
• Each cell surface receptor consists of three components: The intracellular domain, the receptor’s span across the hydrophobic cell membrane, and the extracellular domain. Ligands arrive from the extracellular domain.
• The size and geometry of cell receptor sites varies. This enables cell surface receptors to act in a way similar to a lock for which the ligand is a key.

Those are the basics your students will need to understand about cell surface receptors, but how can they relate this to concepts they have previously studied?

Linking Cell Surface Receptors to Evolutionary Biology

Consider linking cell receptors to evolution, specifically viral evolution. The COVID virus is a great example.

A COVID virus is a strand of RNA in a protein shell. It circulates through the human body until it finds an AR2 (angiotensin 2) receptor. These cell surface receptors abound in the kidney, brainstem, and lung tissue.

But why should COVID attach to human AR2 receptors if it was, as the overwhelming majority of researchers suppose originally a viral infection of bats?

The evolution of COVID to the infectious agent of the current pandemic occurred something like this:

• COVID probably infected two different animals before it infected humans.
• In the animals it infected, COVID had many opportunities to mutate.
• One of those mutations in another animal gave some copies of the COVID virus the ability to bind to AR2 receptors in humans.
• But the mutation that made COVID infectious to humans occurred before the first human was infected.

It goes without saying that your students will not have experience working with COVID, although many of them may have first-hand knowledge of the effects of COVID infection. But your discussion will move even more smoothly if you have previously given your students the first-hand learning experience of relating basic animal physiology to cell biology, Modern Biology Experiment B2. 

Teaching the About the Three Kinds of Cell Surface Receptors

Every biology curriculum will also require teaching about ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.

Ion channel-linked receptors bind to a ligand and open a channel through which the membrane allows specific ions to pass through. There’s no basic example of this effect of insulin.

Your students will understand that insulin signals cells to absorb glucose. They may understand that insulin signals cells to maintain fats in their esterified form, locked in the cell. But they probably will not know that every time insulin sends one molecule of glucose in, it forces two ions of sodium in and three ions of potassium out. 

As this tiny flow of electrostatic energy proceeds, the surface of the cell becomes less and less negatively charged. In time, it becomes so weakly negative that insulin doesn’t move as much glucose into the cell, and the insulin ligand is returned to the bloodstream.

You can then have your students look up the relationship between sodium, potassium, and blood sugar regulation in diabetics.

G-protein-linked receptors bind to ligands that activate a protein in the membrane called a G-protein. This newly activated G-protein activates an ion channel, sending ions in or causing the cell to pump ions out. Or it reacts with an enzyme in the membrane.

G-protein-linked receptors are involved in cyclic processes, like energy production. Your textbook will probably mention the endless cycle of GTP and GDP. Your students can relate this topic to their previous hands-on study of Enzyme Kinetics by Modern Biology.

The third type of cell surface receptor every class will study is the enzyme-linked cell surface receptor. Each of these cell surface receptors is linked with an enzyme. Sometimes the intracellular domain itself is the enzyme.

A key enzyme of this type is a tyrosine kinase, the driver of the transformation of ADP into ATP.  The signal molecule binds to two adjacent tyrosine kinase receptors. The receptors dimerize, joining together. Phosphate groups are added to the tyrosine in the intracellular domain through the process of phosphorylation. Then the phosphorylated tyrosine residues can transmit the signal to make ATP to the next messenger in the cell fluid (cytoplasm).

How Can You Bring All of These Topics Home for Your Students?

We think every class studying cell surface receptors should study their own, personal cell surface receptors. In our experiment EXP-702, Analysis of a Cell-Surface Receptor, students swab their own cheeks for epithelial cells. They use those cells to test for a specific cell surface receptor with a concanavalin A-peroxidase complex in a microscopic assay. 

Then in the second part of the experiment, students investigate a characteristic hemagglutination reaction elicited by concanavalin A. In the course of the experiment, they show that the concanavalin A reaction occurs at multiple receptor sites in their own epithelial cells.

Modern Biology experiments are an important learning tool. They are also an important review tool. Students who have exposure to multiple laboratory learning exercises from Modern Biology develop a framework for adding their understanding of one concept to another, coming back to make the material they learned earlier relevant.

Every Modern Biology experiment kit requires all the test materials, reagents, instructions, and expendable lab supply students need for the lab. Modern Biology experiments aren’t demonstrations. They are experiments, requiring the application of the scientific method. Students generate hypotheses, log data, and apply professional-level analytical tools in reaching their conclusions. Students whose curriculum is complemented by Modern Biology learn more than what’s required to pass the test and build a strong foundation for future biology study.