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In this lesson, we’ll use football to learn about cellular receptors in biology and how they work. We’ll find out what receptors are, where we can find them, and why they’re so important to the human body.

What Is a Receptor?

The eligible receiver, the quarterback, the wide receiver in the end zone – each of these football positions is a type of receptor. Cell receptors work in a similar way to football players: They receive signals and initiate a response. In biology, receptors are proteins or glycoproteins that receive signals by binding to signaling molecules, often called first messengers or ligands, that send a specific signal onward.

The ligand may be an unattached substance, like a chemical, amino acid, protein, lipid, or sugar; ligands can also include hormones, neurotransmitters, or drugs. Some receptors may be affected by environmental factors, like temperature, light, vibration, pressure, or even other receptors. In football, once a player catches the ball, the wide receiver changes his body position so that the ball won’t be lost.

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In biology, receptors can also change their posture, or conformation, in response to ligand binding, which leads to a cascade of chemical reactions called signaling.

Where Do You Find a Receptor?

How does this signaling occur? Well, the process depends on the location of the receptor. Most receptors span the cellular membrane, their parts located both inside and outside of the cell. The ligand binds the part of the receptor found outside of the cell. Inside the cell, we find the receptor’s cytoplasmic site.

Once the ligand binds, it initiates various signaling pathways beginning at the cytoplasmic site, depending on the type of receptor, and often alters the receptor’s conformation.Not all receptors are found in the cellular membrane. Some receptors are located only inside the cell. In these intracellular receptors, their ligand has to get past the cellular membrane, or be a product of the cell. Intracellular receptors often control functions such as gene transcription.

How Does a Receptor Work?

What happens when your favorite team scores a game-winning goal, touchdown, or 3-pointer? You may jump up screaming and celebrating along with your fellow team aficionados.

The players on the field may do a little dance, spike the ball, throw their arms around each other in a big group hug, or give high fives. But what about the losing team and their fans? Some will shake their heads, say ‘good game’, cry, curse, protest, or make excuses for their performance. The range of actions that occur because the ball finds its receptor also happens in cells when ligands bind. Receptors can induce cell growth, division, and death; control membrane channels, or regulate cell binding.

They can cause different physiological responses too, like the feeling of pain or being full after eating.But are receptors really necessary? What happens if the ligand enters the cell and floats around without being snatched by a receptor? Well, what happens when a quarterback throws a football into the end zone and no one catches it? Nothing. On its own, the ligand is powerless. In order for a signaling cascade to take place, ligands must bind their receptors; the receptor initiates everything else. In some cases, many receptors come together to bind one ligand; only when those receptors are brought together by that ligand does the signaling cascade take place.

How a cell responds depends on the types of receptors expressed. For instance, a soccer ball won’t make any difference on a basketball court because the receptor isn’t there for the soccer ball. Cells have their own unique receptor expression, or a difference in receptor number and type, that allows them to act differently to the various stimuli. For this reason, the same ligand can have different effects on a cell, depending on the type of receptors expressed.What happens when the football, instead of being caught by the wide receiver, is caught by the opposing team? An interception occurs, setting into motion a different set of actions. For example, epinephrine can speed up heart rate or open up airways, depending on which kind of receptor the cell expresses. Some ligands, known as antagonists, do not activate the signaling cascade.

By binding, they also stop the receptor from binding other ligands, thus preventing any further developments.

How Do Receptors Prevent Disease?

Receptors are especially important in preventing disease. Cells often use receptors to show the immune cells that they are functioning properly. Inside the cell, cellular products are put on receptors, and the receptors are then moved to the cell surface, where they show their different products. Cells that are not displaying the right products are targeted for destruction by the immune system. How does the immune system know the difference?Receptors. The immune cells also use receptors.

The receptors bind to a different part of the same products that the cells show. Many immune cells also require co-receptors in order to initiate a signaling cascade. These co-receptors recognize a part of the presenting cell’s receptor.The signaling cascade following receptor binding tells the immune cell what to do. Depending on the receptor and type of immune cell, the cascade may eat the presented product, create antibodies, or destroy the cell. In this way, immune cells destroy infected cells and pathogens. This is also why organ transplants may often be rejected.

The immune cells’ receptors start the cascade that recognizes the presented product of a cell from another body as foreign and thus send the signal to attack the transplanted organ.Receptors are also altered in disease states such as cancer. Many receptors function to control cellular proliferation.

Malfunction by mutation or other damage of such receptors often causes uncontrolled cell growth, resulting in cancer.

Lesson Summary

Receptors are proteins or glycoprotein that bind signaling molecules known as first messengers, or ligands. They can initiate a signaling cascade, or chemical response, that induces cell growth, division, and death or opens membrane channels. Receptors can be found both inside and outside the cell, spanning the membrane. They are important because they convey signals via ligand binding. The ligand itself cannot activate the signal; the number and type of cellular receptors expressed control a cell’s response to ligand binding.

Receptors play a major role in aiding the immune system in preventing disease, and receptor malfunction or mutation can be a causative agent of cancer.

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