Cell Communication Quiz

Study Notes

Cells communicate through three main types of signaling: direct contact, local signaling, and long-distance signaling.

Gap junctions (animals) are protein channels that connect adjacent cells enabling the transfer of ions, small molecules, and electrical impulses directly between cells.
Plasmodesmata (plants) are microscopic channels that traverse the cell walls of plant cells.
Juxtacrine signaling involves direct contact between immune cells and their target cells.

Hormone Signaling (Plants): Plants use hormones to communicate over long distances through their vascular tissues.
Endocrine Signaling (Animals): Hormones released by endocrine glands travel to target cells throughout the body via the bloodstream.

Signal transduction is a complex process allowing cells to communicate and respond to their environment. This is the foundation for essential cellular functions, including growth, differentiation, and metabolism.

Reception: A signaling molecule (ligand) binds to a receptor on the target cell’s surface or inside the cell.
Transduction: The signal is converted into a form that can bring about a specific cellular response.
Response: The transduced signal triggers a specific cellular activity.

Ligands: signaling molecules (proteins, peptides, amino acids, steroids, etc.) that bind to receptors.
Receptors: proteins that receive signaling molecules; can be located in the plasma membrane or inside the cell.

Plasma Membrane Receptors: Embedded in the cell membrane, bind to ligands that cannot cross the membrane (e.g., G protein-coupled receptors (GPCRs) and ion channel receptors).
Intracellular Receptors: Found inside the cell (cytoplasm or nucleus), bind to ligands that can cross the cell membrane (e.g., steroid hormones).

Ligand binding causes a change in the receptor's shape, initiating the signal transduction cascade.

Conversion of Signal: The extracellular signal (ligand binding) is converted into an intracellular signal involving multiple molecules.
Phosphorylation and Dephosphorylation:
- Phosphorylation activates proteins by adding phosphate groups (using kinases).
- Dephosphorylation deactivates proteins by removing phosphate groups (using phosphatases).
Amplification via Second Messengers: Second messengers (e.g., cyclic AMP (cAMP)) propagate signals inside the cell, amplifying the signal.