19 - Cell Signaling I

Direct Sinaling

When cells that are directly nect to each other signal one another. Examples: juxtacrine signaling, signaling through gap junctions, signaling through plasmadermata

Justracrine Signaling

A type of direct Cell signaling where receptors on two cell membranes interact with one another to convey a signal. Ex, Antibodes in the immune system.

Signaling Through Gap junctions

A type of direct cell signaling where small molecules pass through neighboring cell gap junctions to convey signals. This process is fast, and is often used to synchronize cells in a small population

Signaling Through Plasmadermata

A type of direct cell signaling

Paracrine Signalinh

A form of cell signaling where a cell produces a signal to induce changes in nearby cells. This process involves the release of signaling molecules that affect neighboring cells, influencing various functions such as growth, differentiation, and immune responses. It plays a crucial role in local cellular communication and tissue regulation. This process is fast, but short lived

Autocrine Signaling

A speciaized type of paracrine signaling where a cell releases a signal that then acts upon its own cell surface; Eg, self cell signaling. Examples incluce pain and inflammation

Neuronal Cell Signaling

A speciaized type of paracrine signaling where neurons signal cells through gap junctions

Endocrine signaling

A form of cell communication where hormones are released into the bloodstream by endocrine glands. These hormones travel long distances to target organs or tissues, influencing various physiological processes. This process of cell signaling is the longest, but it is also the longest lived

Basic Process of Cell Signaling

1. Ligand (the primary messenger) brings to the receptor on a cell

2. Signal transduction from the receptor occurs (sometimes via second messengers)

3. Cellular response (fast when proteins are already made and slow when they need to be synthesized)

   AND/OR

4. Changes in gene expresiion

Properties of Cell Signaling

• Specificity

• Amplifcation

• Desensitization

• Integration

• Localized response

Specificity

1 ligand : 1 receptor : 1 bidning site (with some receptors only being in certain tissues)

Amplification

When enzymes activate other enzymes, the number of effected molecules increases geometrically in an enzyme cascade

Modularity

Proteins with multivalent affinities form diverse signaling complexes from interchangeable parts; phosphorylation provides reversible points of interaction

Desensitization

AKA adaptation; Receptor activation triggers a feedback circut that shuts off the receptor or removes it from the cell surface

Integration

When two signals have opposite effects on a metabolic characteric such as the concentration of a second messenger X, or the membrane potential Vm, the regulatory outcome results from the intragrated input of both receptors

Localized Response

When the enzyme that destroys an intracellular message is clustered with the message producer, the message is degraded before it can diffuse to distant points, so the response is only local and brief

G-Protein Coupled Receptor

An external ligand (L) binding to a receptor (R) activates an intracellular GTP-binding protein (G), which regulates an enzyme (Enz) thar generates an intracellular second messenger (X)

Receptor Enzyme

Ligand binding activates tyrosine kinase activity by autophosphorylation (eg, the receptor themselves is an enzyme)

Kinase Cascade

Kinase activates activation factor (T), altering gene expression

Gated Ion Channel

Channel opens or closes in response to concentration in reponse to signal ligand or membrane potential

Nuclear Receptor

Hormone binding allows the receptor to regulate the expression of specific genes

The three G proteins

alpha, beta, and gamma

Process of GPCR signaling

1. resting state → receptor not bound to ligand; Ga is bound to GDP (inactive) and associated with Gby; G proteins are not connected to the receptor at this point

2. Ligand binding → this activates the receptor and it binds a G protein, Ga releases GDP and binds GTP

3. Ga separates from Gby and moves along the membrane to bind elsewhere

4. Ga protein activates or inhibits terget proteins, initiating signal tranduction events

5. Ga hydrolyzes its bound GTP → GDP, becoming inactive

6. Gby dissociates from receptor and rejoin Ga, forming an inactive G protein

Epinephrine Signaling

1. Epi binds to its specific receptor → Beta andregenic receptor

2. Hormone receptor