Unit 2 cell communication

What are the two main mechanisms of cell communication?

Direct contact and extracellular messengers.

What are gap junctions?

Tunnels formed by connexons that connect cells, allowing ions and small water-soluble chemicals to pass between them (e.g., in cardiac and smooth muscle).

What is cell-to-cell recognition?

Interaction between cell-surface molecules that allows cells to recognize each other (e.g., immune cells identifying self vs. non-self).

How do extracellular messengers communicate?

Cells release ligands that bind to receptors on target cells to trigger a response.

What are local regulators?

Molecules like paracrine and autocrine signals that act near their site of release.

What is paracrine communication?

Ligands diffuse locally to affect nearby cells (e.g., histamine, cytokines, prostaglandins).

What is autocrine communication?

A cell releases a chemical that acts on itself.

What are neurotransmitters?

Chemicals secreted by neurons that diffuse across a synaptic cleft to affect an adjacent cell; short-lived.

What are neurohormones?

Hormones secreted by neurons into the blood (e.g., oxytocin, antidiuretic hormone).

What are hormones?

Long-range chemical messengers that travel through the blood to distant target cells.

How do lipid-soluble hormones act?

They pass through the plasma membrane, bind to intracellular receptors, and trigger gene transcription to produce new proteins.

How do water-soluble hormones act?

They bind to membrane-bound receptors, causing a conformational change that activates ion channels or second-messenger systems.

How are hydrophilic (water-loving) hormones transported?

Dissolved directly in plasma (e.g., peptide hormones, catecholamines).

How are lipophilic (lipid-soluble) hormones transported?

Bound to plasma proteins like albumin (e.g., steroid and thyroid hormones)

What are secondary messengers?

Molecules that amplify a cell’s response to signals inside the cell (e.g., cAMP, calcium).

What is the general mechanism of the cAMP signal transduction pathway?

1. G protein activates adenylyl cyclase.

2. ATP is converted to cyclic AMP.

3. cAMP activates protein kinase A.

4. Protein kinase A phosphorylates proteins to trigger responses.

What is the general mechanism of the calcium signal transduction pathway?

1. Messenger binds to G protein or tyrosine kinase receptor.

2. Activates phospholipase C, converting PIP2 into DAG and IP3.

3. DAG activates protein kinase C.

4. IP3 releases calcium from ER.

5. Calcium binds to calmodulin to trigger responses.