Intracellular signal transduction. Definition: The process in which a signal is passed on to downstream components within the cell, which become activated. In most cases, a chain of reactions transmits signals from the cell surface to a variety of intracellular targets—a process called intracellular signal transduction. The targets of such signaling pathways frequently include transcription factors that function to regulate gene expression.‎The cAMP Pathway · ‎Cyclic GMP · ‎Phospholipids and Ca2+. Jump to Extracellular receptors - Extracellular receptors. Signal transduction occurs as a result of a ligand binding to the outside region of the receptor (the ligand does not pass through the membrane). Ligand-receptor binding induces a change in the conformation of the inside part of the receptor, a process sometimes called "receptor activation".‎Stimuli · ‎Receptors · ‎Intracellular receptors · ‎Second messengers.


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Although most effects of cAMP are mediated by protein kinase Intracellular signal transductioncAMP can also directly regulate ion channels, independent of protein phosphorylation. Cyclic AMP functions in this way as a second messenger involved in sensing smells.

Signal transduction - Wikipedia

Many of the odorant receptors in sensory neurons in the nose are G protein-coupled receptors that stimulate adenylyl cyclaseleading to an increase in intracellular cAMP. As discussed earlier in intracellular signal transduction chapter, different types of guanylyl cyclases are activated by both nitric oxide and peptide ligands.

Stimulation of these guanylyl cyclases leads to elevated levels of cGMP, which then mediate biological responses, such as blood vessel dilation. The action of cGMP is frequently mediated by activation of a cGMP-dependent protein kinasealthough cGMP can also act intracellular signal transduction regulate other targets, including ion channels.

Signal relay pathways

The best-characterized role of cGMP is in the vertebrate eye, where it serves as the second messenger responsible for converting the visual signals received as light to nerve impulses. The photoreceptor in intracellular signal transduction cells of the retina is a G protein-coupled receptor called rhodopsin Figure Rhodopsin is activated as a result of the absorption of light by the intracellular signal transduction small molecule cis-retinal, which then isomerizes to all-trans-retinal, inducing a conformational change in the rhodopsin protein.

This change in cGMP level in retinal rod cells is translated to a nerve impulse by a direct effect of cGMP on ion channels in the plasma membranesimilar to the action of cAMP in sensing smells.

Role of cGMP in photoreception. Absorption of light by retinal activates the G protein-coupled receptor rhodopsin.

Pathways of Intracellular Signal Transduction - The Cell - NCBI Bookshelf

PIP2 is a minor component of the plasma membranelocalized to the intracellular signal transduction leaflet of the phospholipid bilayer see Figure Retinoic acid receptors are another subset of nuclear receptors.

They can be activated intracellular signal transduction an endocrine-synthesized ligand that entered the cell by diffusion, a ligand synthesised from a precursor like retinol brought to the cell through the bloodstream or a completely intracellularly synthesised ligand like prostaglandin. These receptors are located in the nucleus and are not accompanied by HSPs.

They repress their gene by binding to their specific DNA sequence when no ligand binds to them, and vice versa.

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Certain intracellular receptors of the immune system are cytoplasmic receptors; recently identified NOD-like receptors NLRs reside in the cytoplasm of some eukaryotic cells and interact with ligands using a leucine-rich repeat LRR motif similar to TLRs.

Second messengers are the substances that enter the cytoplasm and act within the cell intracellular signal transduction trigger a response.


In essence, second messengers serve as chemical relays from the plasma membrane to intracellular signal transduction cytoplasm, thus carrying out intracellular signal transduction. Calcium[ edit ] The release of calcium ions from the endoplasmic reticulum into the cytosol results in its binding to signaling proteins that are then activated; it is then intracellular signal transduction in the smooth endoplasmic reticulum [47] and the mitochondria.

The nature of calcium in the cytosol means that it is active for only a very short time, meaning its free state concentration is very low and is mostly bound to organelle molecules like calreticulin when inactive.

Calcium is used in many processes including muscle contraction, neurotransmitter release from nerve endings, and cell migration.

Cell signaling | Biology | Science | Khan Academy

The three main pathways that lead to its activation are GPCR pathways, RTK pathways, and gated ion intracellular signal transduction it regulates proteins either directly or by binding to an enzyme.

Lipid messengers[ edit ] Lipophilic second messenger molecules are derived from lipids residing in cellular membranes; enzymes stimulated by activated receptors activate the lipids by modifying them. Examples include diacylglycerol and ceramidethe former required for the activation of protein kinase C.

Nitric oxide[ edit ] Nitric oxide NO acts as a second messenger because it is a free intracellular signal transduction that can diffuse through the plasma membrane and affect nearby cells.

It is synthesised from arginine and oxygen by the NO synthase and works through activation of soluble guanylyl cyclasewhich intracellular signal transduction activated produces another intracellular signal transduction messenger, cGMP. NO can also act through covalent modification of proteins or their metal co-factors; some have a redox mechanism and are reversible.

It is toxic in high concentrations and causes damage during strokebut is the cause of many other functions like relaxation of blood vessels, apoptosisand penile erections.


Redox signaling[ edit ] In addition intracellular signal transduction nitric oxide, other electronically activated species are also signal-transducing agents in a process called redox signaling.

Examples include superoxidehydrogen peroxidecarbon monoxideand hydrogen sulfide.

Hormones and growth factors are forms of signal molecules that bind to a specific receptor and cause a specific reaction during intercellular signal transduction.

Intercellular signal transduction via receptors is a very important mechanism intracellular signal transduction homeostasis. The answer comes down to basic biochemistry: