Name: cell-surface receptor signal cascades
Uploaded: 2026-08-26T08:20:17.575Z
Duration: 1 min 43 s
Channel: JoVE

Intracellular signaling pathways relay and amplify extracellular signals into the cell interior.Several signaling pathways, such as the cyclic AMP, MAPK/ERK, and IP3/DAG pathways, transmit and amplify signals. These signals can change gene expression or cell metabolism.For example, the cyclic AMP signaling pathway can be activated by external ligands, such as adrenaline, that bind to transmembrane G protein-coupled receptors, or GPCRs.Ligand binding changes the shape of the GPCR, allowing it to interact with and activate a G protein on the inside of the cell.Then, the GDP on the G&#x3B1; subunit is replaced by GTP, allowing the G&#x3B1; subunit to separate from the G&#x3B2;&#x3B3; dimer.The activated G&#x3B1; subunit stimulates the enzyme adenylyl cyclase, which converts ATP into cyclic AMP, or cAMP.Once activated, adenylyl cyclase produces many cAMP molecules. As a result, the signal is amplified.cAMP acts as a second messenger and activates cytosolic protein kinase A, or PKA, by causing its regulatory and catalytic subunits to separate.PKA uses ATP to phosphorylate many target proteins, including transcription factors that regulate gene expression.

intracellular signaling cascades

Intracellular Signaling Cascades

Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. The continuation of a signal in this manner is called signal transduction. Signal transduction only occurs with cell-surface receptors, which cannot interact with most components of the cell, such as DNA. Only internal receptors can interact directly with DNA in the nucleus to initiate protein synthesis. When a ligand binds to its receptor, conformational changes occur that affect the receptor&#x27;s intracellular domain. Conformational changes of the extracellular domain upon ligand binding can propagate through the membrane region of the receptor and lead to activation of the intracellular domain or its associated proteins.After the ligand binds to the cell-surface receptor, the activation of the receptor&#x27;s intracellular components sets off a chain of events that is called a signaling pathway or a signaling cascade. In a signaling pathway, second messengers&#x2013;enzymes&#x2013;and activated proteins interact with specific proteins, which are then activated in a chain reaction that eventually leads to a change in the cell&#x27;s environment, such as an increase in metabolism or specific gene expression. The events in the cascade occur in a series like how a current flows in a river. Interactions that occur before a certain point are defined as upstream events, and events after that point are called downstream events.Signaling pathways can get very complicated very quickly because most cellular proteins can affect different downstream events, depending on the conditions within the cell. A single pathway can branch off toward different endpoints based on the interplay between two or more signaling pathways, and the same ligands are often used to initiate different signals in different cell types. This variation in response is due to differences in protein expression in different cell types. Another complicating element is signal integration of the pathways, in which signals from two or more different cell-surface receptors merge to activate the same response in the cell. This process can ensure that multiple external requirements are met before a cell commits to a specific response.The effects of extracellular signals can also be amplified by enzymatic cascades. At the initiation of the signal, a single ligand binds to a single receptor. However, activation of a receptor-linked enzyme can activate many copies of a component of the signaling cascade, which amplifies the signal.This text is adapted from <a href="https://openstax.org/books/biology-2e/pages/9-2-propagation-of-the-signal">Openstax, Biology 2e, Section 9.2: Propagation of the Signal</a>.

Once a ligand binds to a receptor, the signal is transmitted through the membrane and into the cytoplasm. The continuation of a signal in this manner is ...

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Cellular Processes

Cell Signaling

KEY TERMS AND CONCEPTS

cell-surface receptor signal cascades

Cell-surface receptor signal cascades move information from outside the cell into the cytoplasm. This process is called signal transduction. It happens only with cell-surface receptors, because they cannot interact with most cell parts, such as DNA.

Internal receptors are different. They can interact directly with DNA in the nucleus and help start protein synthesis. When a ligand binds to a receptor, the receptor changes shape. That shape change affects the receptor’s intracellular domain or the proteins attached to it.

This activation starts a signaling pathway, also called a signaling cascade. In the pathway, second messengers, enzymes, and activated proteins work with specific proteins in a chain reaction. The result can be a change in the cell’s environment, such as increased metabolism or specific gene expression.

These events happen in order, like current moving through a river. Events before a chosen point are upstream, and events after that point are downstream. Signaling pathways can become complex because many cellular proteins can affect different downstream events depending on the conditions inside the cell.

A single pathway can also branch to different endpoints. The same ligand may trigger different signals in different cell types because those cells express different proteins. Cells can also use signal integration, where signals from two or more cell-surface receptors merge to produce the same response. This helps ensure that multiple outside conditions are met before the cell commits to one response.

Signals can be amplified as well. At the start, one ligand binds to one receptor. Then a receptor-linked enzyme can activate many copies of a component in the cascade. This makes the signal stronger as it moves through the pathway.

Cell-Surface Receptor Signal Cascades

what is cell signaling?

How Cells Send and Receive Signals

Cell signaling lets cells send and receive messages from the environment and from other cells. Even with a protective membrane, cells need to detect changes and respond to them. Unicellular and multicellular organisms use signaling to stay coordinated and to react to outside cues. Cells often rely on receptor proteins in the membrane to sense information. Skin cells can respond to touch, and photoreceptors in the retina can detect light. Most cells respond to chemical signals such as hormones,...

internal receptors

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contact-dependent cell communication

Cell-to-Cell Signaling via Channels

Cell-to-cell signaling can happen when neighboring cells are in direct contact. In this kind of communication, cells use receptor-ligand interactions or special cytoplasmic channels to move small molecules between them. In animal cells, these channels are called gap junctions. They form when six proteins called connexins assemble into a cylindrical structure in the plasma membrane called a connexon. When connexons from two adjacent cells line up, a channel opens between the cells. Enzymes help...

autocrine signaling

Self-Signaling Cells in Immunity and Cancer

Autocrine signaling is a cell communication method in which a cell sends a signal to itself. The same cell releases an extracellular signaling molecule and also has receptors that can bind to that molecule. This lets the cell respond to its own message. In the immune system, this process is important for homeostasis, or keeping body conditions stable. A well-studied example is the macrophage, an immune cell that secretes cytokines such as interleukin-1, or IL-1. Macrophages also have membrane...

paracrine signaling

Local Cell Signaling in Blood and Healing

Local cell signaling helps cells communicate with nearby neighbors using released signaling molecules. These molecules act only over a short distance because they break down quickly or are inactivated if they are not taken up. This type of signaling supports processes such as nitric oxide signaling in blood vessels, neuron-to-neuron communication at synapses, blood clotting, tissue repair, and local allergic skin reactions. A clear example is nitric oxide signaling in blood vessels. The...

synaptic signaling

Chemical and Electrical Synapses

Neurons send signals across synapses, which are junctions between cells. These signals can excite or inhibit other neurons or target cells such as muscles. Most synapses are chemical. Some are electrical. Chemical synapses use action potentials, which are electrical impulses, to trigger the release of neurotransmitters. The sending neuron is the presynaptic neuron, and the receiving neuron is the postsynaptic neuron. An action potential travels along the axon and reaches the axon terminal,...

endocrine signaling

Hormones Travel to Distant Target Cells

Endocrine signaling uses hormones to send messages to target cells in other organs. Endocrine cells release these hormones into the circulatory system, which carries the signal through the body. Because the hormone reaches the whole organism, only cells with the right receptors respond. This kind of signaling usually acts slowly, but its effects last longer. Endocrine cells can use cell surface receptors or intracellular receptors, depending on the hormone. Cell surface receptors are...

bacterial signaling

Quorum Sensing in Bacteria

Quorum sensing lets bacteria coordinate behavior by sensing how many cells are nearby. Bacteria can signal inside the cell or between cells. When many bacteria act together, they can behave like a community and change gene expression as a group. This signaling starts with autoinducers, or AIs. Individual bacteria make AIs and release them across the cell membrane into the surrounding space. Some AIs diffuse out passively along a concentration gradient, while others are moved out by active...

yeast signaling

Yeast Cell Communication in Mating

Yeast cell communication helps control mating, colony growth, and other cell responses. Yeasts are single-celled organisms, but unlike bacteria, they are eukaryotes with a nucleus. Their signaling works much like cell signaling in other eukaryotic cells. A signal often begins when a ligand, such as a protein or small molecule released from a yeast cell, binds to a receptor on the cell surface. This binding activates second-messenger kinases, which then switch transcription factors on or off.

g protein-coupled receptors

GPCR Signaling Through G Proteins

G-protein coupled receptors, or GPCRs, start cell signaling after a ligand binds to the receptor. The receptor is a single polypeptide that crosses the cell membrane seven times. These membrane loops create an outside pocket that fits a specific ligand, such as a neurotransmitter or hormone. The inside loops connect to a G-protein.

enzyme-linked receptors

Trk Receptors in Cell Signaling

Trk receptors are enzyme-linked receptors that help cells respond to growth factors and some hormones. They belong to the receptor tyrosine kinase, or RTK, family. These receptors can trigger several signals inside a cell after they are activated. Neurotrophin receptors are one RTK group and include TrkA, TrkB, and TrkC, which are tropomyosin-related kinase receptors. TrkA binds nerve growth factor, neurotrophin-6, and neurotrophin-7. TrkB binds brain-derived neurotrophic factor, or BDNF, and...

ion channels

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Ion channels are membrane proteins that help cells move ions across the plasma membrane. Ions such as sodium, potassium, and calcium move into and out of cells to maintain the electrochemical gradient. This gradient supports cell size and volume, nerve signaling, and gas and nutrient exchange. Ion channels are specialized integral membrane proteins that let specific ions pass down their electrochemical gradient. Their main job is to help keep the membrane potential, which is needed for cell...

what are second messengers?

Cell Signals That Use Second Messengers

Cell signals often use second messengers to carry messages inside the cell. Many receptor-binding ligands are hydrophilic, so they do not cross the cell membrane. Instead, the signal is relayed to an internal messenger that can spread the message farther. G-protein coupled receptors can activate the phosphoinositol pathway and the cyclic AMP, or cAMP, pathway. In the phosphoinositol pathway, the receptor activates phospholipase C. This enzyme hydrolyzes phosphatidylinositol biphosphate, or...

Cell-surface receptor signal cascades move information from outside the cell into the cytoplasm. This process is called signal transduction. It happens only with cell-surface receptors, because they cannot interact with most cell parts, such as DNA. Internal receptors are different. They can interact directly with DNA in the nucleus and help start protein synthesis. When a ligand binds to a receptor, the receptor changes shape. That shape change affects the receptor’s intracellular domain or...

key terms and concepts

Explore how cell-surface receptors pass signals into the cell, trigger cascades, branch into different responses, and amplify messages in high school biology.

Cell-Surface Receptor Signal Cascades | JoVE K12

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Cell-Surface Receptor Signal Cascades

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