Cell Communication Basics
The many distinct ways that cell communication is the subject of this portion of the AP Biology curriculum. We’ll begin by looking at the signal transduction process. This happens when a ligand or physical signal activates a receptor protein, causing it to catalyse a reaction on the interior of the cell membrane. Signal transduction then triggers a chain of events that goes from the original receptor protein to a biological response.
We’ll look at how various types of cellular communication are categorised based on the distance the signal must travel once we’ve looked at this procedure. Many immune system responses are triggered by cell-to-cell contact, as we’ll see. Then we’ll look at certain paracrine signals that only influence surrounding cells, such as neurotransmitters. Finally, we’ll examine how the endocrine system coordinates an organism-wide reaction to a stimulus by sending endocrine signals throughout the body!
Cell Communication Overview
Our phones can connect with one another via touch and NFC protocols, allowing us to “tap and pay.” They can communicate over a medium distance via Bluetooth signals and WiFi networks, allowing us to access the internet while wearing headphones. They can even make a video call to someone on the other side of the planet by connecting to a cell tower thousands of kilometres away. This is all rather incredible. But did you realise that cells have been communicating for billions of years using very similar mechanisms?
Cells may interact with one another in a number of different ways. Contact allows certain cells to interact with their neighbours. Others communicate with surrounding cells via short-range signals. Some cells are even in charge of producing hormone molecules, which move throughout the body and impact cells in a variety of tissues and organs. This knowledge will undoubtedly be included on the AP exam. Stay with us as we go through the fundamentals of mobile communication!
Cell Communication Signal Transduction
Let’s start with an explanation of how cell signalling works. Signal transduction is the process of a signal generating a certain response in another cell. Though we’ll go through signal transduction routes in more depth in the next sections, most signal transduction pathways have a common structure.
The majority of signals begin when a signal is received by a protein on the cell’s surface. The signal might be chemical or physical in nature, such as touch, light, or sound waves. Each receptor protein has evolved to receive a highly particular signal, which is referred to as a ligand in the case of a chemical signal.
When a signal is received, the receptor protein catalyses a process in the interior of the cell. Signal transduction is the process of a reaction’s result starting a cascade of subsequent reactions. The end result of this chain reaction is a biological response. Depending on the cell signal obtained, responses might vary substantially.
When receptors on the cell surface alert an immune cell that it is in touch with an invading bacterial cell, for example, the immune cell may commence phagocytosis. Alternatively, when a muscle cell receives insulin, its insulin receptors activate a chain of events that induce the cell to send glucose importers to the cell membrane and import as much glucose as possible.
Because cell communication may cause literally millions of distinct and precise responses, the simplest way to categorise it is by the distance the signal must travel. Certain signals can only be transmitted when two cells are in direct contact. The most common way for this to happen is for two cells’ surface proteins to link together. Cells sending chemical messages via holes, such as the plasmodesmata in plants that link two or more cells, are another example.
Cell Communication Chemical Messengers
While touch plays a role in cell communication, chemical messengers are responsible for the vast majority of cell messages. Autocrine signals are chemical communications that influence the same cell from which they come. Because local regulator chemicals like neurotransmitters only impact adjacent cells, they are referred to as “paracrine signals.” Finally, of all the chemical communication techniques, endocrine signalling spans the greatest distance. Endocrine glands release hormones and other signalling chemicals into the circulation, which impact target cells all throughout the body!
Consider this… Your body’s cells must communicate for the same reasons that ants in a colony must communicate. Each ant must be aware of when it is time to gather food, when it is time to defend itself, and when it is time to relax. Try to remember that the ultimate reason cells interact is to coordinate their functions in support of the organism as a whole as we go further into the many mechanisms of cell communication.
A huge number of cells employ cell-to-cell contact to send and receive some of the most crucial messages that cells in organisms must communicate. This kind of cell communication is similar to a handshake. While there are several instances, we’ll focus on a few of the most essential cellular signals that are transmitted via cell-to-cell communication.
Take a look at what occurs in your body while regular cells develop. When these cells collide with other cells, proteins on the cell’s surface become active, signalling the cell to stop growing. This is why healthy tissues are so well-organized and uniform. Many cancer cells have disrupted signal transduction pathways, which is why they continue to divide in an unorganised manner, developing into deformed tumours and invading other regions of your body!
Consider one of your body’s most essential cell communication pathways: the one that enables your immune cells to detect and eliminate invading invaders such as viruses and bacteria. Cell-to-cell contact signal transduction pathways are used by almost every element of your immune system, from white blood cells that collect and destroy invading germs to cells that produce and release antibodies to fight illnesses.
While it is not necessary to recall the complete immune system at this point, it is crucial to understand that different cells respond differently when they come into contact with another cell. When a phagocytic antigen-presenting cell trains helper T-cells, they learn how to recognise the antigen of an invading virus or bacterium. Then, via yet another cell-to-cell interaction, helper T-cells may “train” B-cells, which then go on to manufacture the antibodies that an organism needs to combat infection!
There are several distinct types of local regulator molecules that only impact cells in close proximity to each other. Paracrine signals are a term used to describe these signals. Neurotransmitters are the most common paracrine substances found in the human body. Neurotransmitters are chemicals that enable nerve signals to go from one nerve cell to the next.
When a nerve impulse going along the first neuron reaches a voltage-gated ion channel, a complicated process begins. Calcium ions may now overwhelm the transmitting neuron. Synaptic vesicles combine with the cell membrane as a result of the calcium influx, prompting neurotransmitters to be released into the synaptic space. These neurotransmitters attach to ligand-gated channels in the receiving neuron, triggering an influx of sodium ions. This sudden influx of ions depolarizes the membrane, prompting a cascade of ion channels to open and carry the signal along the length of the neuron.
This isn’t the only example of a local regulator molecule in action. In reality, bacterial cells have a very fascinating kind of local regulator communication. When bacteria develop biofilms with other bacteria, they have a better chance of surviving. Biofilms, on the other hand, can only develop when bacterial cells are evenly spaced.
This implies that the bacteria must stop dividing and collaborate to excrete chemicals in order to form a solid biofilm that will protect them. Each bacteria secretes a small quantity of a local regulator molecule as it grows. When bacterial cells reach a particular density, the concentration of local regulator molecules induces the bacteria to change their metabolism and release biofilm chemicals!
Cell Communication Endocrine signals
Long-distance cell communication is the final kind of cell communication. These are known as endocrine signals inside an organism, and they are regulated and released by the endocrine system. Because it continually coordinates the functions of your body by producing a broad range of hormones from many organs, the endocrine system is very complicated. These hormones go through your circulation and attach to receptor proteins on a variety of target cells in various tissues and organs.
Take, for example, the pancreas’ complicated job of controlling blood glucose levels in the body. Glucose importers transport glucose into beta cells in the pancreas when blood glucose levels are high. This stimulates a signal transduction route in the beta cells, causing insulin to be excreted. Insulin circulates in the bloodstream, where it attaches to insulin receptor proteins on cells all throughout the body.
Insulin attaches to liver cells and sends a signal to the liver, causing it to store glucose as glycogen. When insulin attaches to receptors on other tissues in your body, it triggers a chain of events that induces vesicles containing glucose-importers to connect to the cell membrane. This causes a flood of glucose to be imported from the circulation into each cell.
When your blood glucose levels begin to decline, your pancreas secretes glucagon. This hormone instructs the liver to turn glycogen back into glucose by binding to receptors on liver cells. This helps to keep your blood sugar levels in check until your next meal.
Keep in mind that all of these intricate kinds of cell communication across numerous organ systems and tissues are only necessary to keep your blood glucose levels within a certain range. Your endocrine system is continually secreting hormones for a number of reasons, causing a wide range of responses in various cell types throughout your body.