Signal Transduction and G-Proteins

A membrane-bound protein composed of three subunits (alpha, beta, and gamma). The alpha subunit has a binding site for GDP, which is non-covalently bound.

The interaction between a receptor and a Gs-protein where the ligand binds to the receptor, causing a conformational change that allows the receptor to interact with the Gs-protein.

The process by which the ligand binds to the receptor, causing a conformational change in the receptor that opens the binding site for the Gs-protein.

When a ligand binds to a receptor, it activates multiple Gs-proteins, amplifying the initial signal. This allows for a strong cellular response.

The alpha subunit of the Gs-protein, after being activated by GTP binding, carries the signal to the next stage of the transduction pathway.

The process where GDP bound to the alpha subunit is replaced by GTP, causing a conformational change and activation of the Gs-protein.

The Gs-protein, after being activated by GTP binding, undergoes a conformational change and fragments. The alpha subunit with bound GTP is released from the beta and gamma subunits, which remain associated.

The process repeats for as long as the ligand is bound to the receptor, allowing persistent signal transduction.

Cyclic AMP binds to protein kinase A (PKA), activating it by causing a conformational change. This allows PKA to phosphorylate other proteins, initiating a signal cascade.

Adrenaline, a hormone released during stress, binds to β-adrenoreceptors on liver cells. This activates adenylate cyclase, increasing cAMP production, which ultimately leads to the breakdown of glycogen.

The effect of adrenaline on liver cells is coordinated: it promotes glycogen breakdown while inhibiting glycogen synthesis, maximizing energy release.

Theophylline and caffeine both inhibit phosphodiesterases, the enzymes responsible for breaking down cAMP. This leads to an increase in cAMP levels and prolonged signal transduction.

Gi proteins bind to different receptors than Gs proteins, but the activation mechanism is identical. They inhibit adenylate cyclase, reducing cAMP levels. This creates a 'brake' and 'accelerator' system for cAMP signaling.

This enzyme converts ATP into cyclic AMP (cAMP), a crucial molecule in cell signaling.

A signal amplification mechanism where one active αs-GTP molecule can activate numerous adenylate cyclase molecules, leading to the production of many cAMP molecules.

A small molecule that acts as a secondary messenger within cells, transmitting signals initiated by the binding of extracellular molecules to receptors. It's produced by adenylate cyclase.

An enzyme involved in the phosphorylation of serine and threonine residues on proteins. It is activated by cyclic AMP.

The process of adding a phosphate group to a protein, often altering its activity and changing the way the cell responds to a signal.

Specific regions on proteins where phosphate groups are added by protein kinases. Often involved in regulating protein activity.

This protein is composed of two regulatory (R) and two catalytic (C) subunits. Cyclic AMP binding to the regulatory subunits releases and activates the catalytic subunits, allowing them to phosphorylate other proteins.

A molecule found in the cell membrane that is cleaved by phospholipase C (PLC) into two signaling molecules: inositol triphosphate (IP3) and diacylglycerol (DAG).

An enzyme that hydrolyses PIP2, generating inositol triphosphate (IP3) and diacylglycerol (DAG) as second messengers.

A water-soluble molecule that diffuses into the cytoplasm and binds to receptors on the endoplasmic reticulum, triggering the release of calcium ions.

A lipid molecule that remains in the cell membrane and activates protein kinase C (PKC).

A positively charged ion that is released from intracellular stores (e.g., the endoplasmic reticulum) in response to IP3. It acts as a second messenger and regulates various cellular processes.

Enzymes that add phosphate groups to proteins, often altering their activity and triggering downstream cellular responses.

The process by which cells receive and respond to signals from their environment. It often involves a series of steps that involve the activation of protein kinases and other enzymes.

IP3, a product of PIP2 breakdown, binds to receptors on intracellular calcium stores, triggering the release of calcium into the cytoplasm. This influx of calcium activates various proteins and enzymes involved in cellular processes.

Calcium ions (Ca++) bind to calmodulin, a protein involved in regulating cellular processes. This calcium-calmodulin complex activates other proteins, ultimately leading to changes in enzyme activity and gene expression.

The breakdown products of PIP2, IP3 and DAG, are eventually recycled back into PIP2. This recycling ensures a continuous supply of PIP2 for signal transduction.

Tyrosine kinase is an enzyme that catalyzes the transfer of a phosphate group from ATP to the amino acid tyrosine on a protein. This phosphorylation modifies the protein's activity and can trigger downstream signaling events.

A ligand binding to a tyrosine kinase receptor activates its intrinsic kinase activity. The activated receptor then phosphorylates itself and other signaling proteins, initiating a cascade of events that ultimately leads to cellular responses.

Tyrosine kinase-linked receptors are activated by the binding of a ligand, which causes them to dimerize (form a pair). This dimerization brings the kinase domains of the receptors together, allowing them to phosphorylate each other on specific tyrosine residues.

Phosphorylated tyrosine residues on the receptor serve as docking sites for other signaling proteins, initiating a cascade of downstream signaling events. This allows the signal to be amplified and transmitted further into the cell.

The intracellular signaling pathways initiated by tyrosine kinase-linked receptors involve a variety of signaling proteins, including PLCγ, Grb2, and Ras. These proteins interact with each other and with other components of the signaling cascade, ultimately leading to changes in gene expression, cell growth, or other cellular processes.

The association of Grb2 and SoS with the phosphorylated receptor leads to their activation and subsequent interactions with Ras. This leads to Ras activation through the exchange of GDP for GTP, driving a further cascade of signaling events.

Ras is a small GTPase protein that acts as a molecular switch, cycling between an inactive GDP-bound state and an active GTP-bound state. Active Ras transmits signals to downstream signaling pathways, ultimately leading to cellular responses such as proliferation, differentiation, or survival.

After a ligand binds to a tyrosine kinase-linked receptor, a cascade of events occurs. These events include receptor dimerization, phosphorylation, binding of signaling proteins, activation of downstream pathways, and ultimately changes in cellular function.

Examples of tyrosine kinase-linked receptors include receptors for growth factors, cytokines, and insulin. These receptors play crucial roles in regulating cell growth and development.