Ch 7: cell communication

Local cell communication

Occurs between adjacent cells or through cell-cell interaction.

Long distance cell communication

Occurs through external signals

Intracellular communication

Communication occurs within the cell itself

Intercellular communication

Communication between cells close to or far away from each other. Signals are secreted through the gap junction or communicated by the cell surface proteins on the plasma membrane of the signaling cell to another cell close by (local signaling) or from the endocrine cells to cells located far away.

Ligand

A signal molecule that binds to a receptor protein.

Signal transduction

The process that includes reception (ligand binding to receptor), transduction (converting signal into a cellular response), and cellular response to a signal.

Protein kinase cascade

A series of protein modifications that amplify a signal, such as in the epinephrine pathway (one receptor activation can lead to the production of many glucose molecules).

Crosstalk

Interactions between different signaling pathways that can lead to additive or higher responses.

Plasma membrane localized receptors

These are cell surface receptors that interact with hydrophilic small or large molecules. E.g. epinephrine and insulin proteins.

G-protein coupled receptors

Receptors that interact with hydrophilic molecules and undergo conformational changes upon ligand binding.

G-proteins and how they change

Proteins that bind GTP, dissociate, and activate enzymes like adenylyl cyclase.

G-protein action and cell response

• A ligand binds to a receptor then there is a change in receptor conformation.

• The receptor binds inactive G Protein which has bound GDP.

• The G protein then loses the bound GDP and binds GTP.

• It is now an active G protein and dissociates from receptor.

• The active G protein then binds to another protein, which changes its activity and sends a signal into the cell.

• When the ligand is no longer present, the receptor stops simulating the formation of the GTP form of the G protein and the proteins will restore themselves to being GDP bound and become inactive.

Epinephrine pathway in skeletal muscle and liver

Epinephrine binds to receptor, activates G protein, stimulates adenylyl cyclase to produce cAMP, cAMP activates protein kinase A, which then activates phosphorylase kinase and glycogen phosphorylase, leading to glucose production from glycogen

Resting State Reinstatement

Occurs when ligand concentration drops and the receptor is no longer binding ligand, leading to inactive G proteins becoming dominant, adenylyl cyclase is no longer stimulated, cAMP synthesis drops, and protein phosphatases inactivate phosphorylated proteins.

Tyrosine Kinase Receptors conformational changes

Receptors that undergo conformational changes upon ligand binding, and aggregate to form a dimer

Autophosphorylation

A process where kinase activity leads to phosphorylation on tyrosine residues, allowing the receptor to return to an inactive state.

Relay Proteins

Phosphorylated receptors bind multiple SH2 domain-containing proteins, activating various signal transduction pathways.

Tyrosine Receptor Kinase Pathway on calcium

• A ligand binds to a receptor

• PLC is activated and Insp3 is produced

• Ca2+ is released from the ER/mitochondria

• Ca2+ binds and stimulates other proteins leading to responses

• The resting state is reinstated once the ligand concentration has dropped and the receptor is no longer binding ligand.

Ion Channel Receptors

• ligand interacts with a receptor which is a transmembrane protein

• protein changes conformation from closed channel state to open channel state

• specific ion(s) can move through according to the electrochemical gradient.

Intracellular Receptors

Receptors that interact with steroid ligands in the cytoplasm

Receptor-ligand complex enters the nucleus and stimulate mRNA synthesis from certain genes that would lead to increased amounts of certain proteins in the cell.