BIOL 1406 Chapter 11 Lecture Slides

Chapter 11: Cell Communication

Cellular Communication

  • Overview: Cells interact with their environments and each other to coordinate responses to stimuli such as chemical signals.

  • Functions:

    • Recognize and respond to stimuli (chemical signals).

    • Transport materials in and out of the cell.

    • Join together to form tissues.

    • Transmit and receive chemical signals.

    • Coordinate cellular responses.

Cell-Cell Recognition

  • Mechanism: Cells recognize each other by binding to surface molecules, typically carbohydrates on the plasma membrane.

  • Components:

    • Membrane carbohydrates can be in the form of glycolipids or glycoproteins.

    • Carbohydrate types vary among species, individuals, and cell types.

Steps in Cell Communication

  • Process Flow:

    1. Molecules interact.

    2. Interaction prompts a change in protein conformation.

    3. Changed conformation alters protein function.

Local Signaling

  • Definition: Communicates with nearby cells only.

  • Examples:

    • Direct contact / cell-cell recognition: Immediate recognition.

    • Plasmodesmata & Gap Junctions: Connect cytoplasm of adjacent cells, allowing direct signaling.

    • Paracrine Signaling: General signals that affect nearby cells.

    • Synaptic Signaling: Specific signals used by nerve cells.

Mechanism of Local Signaling

  • Local regulator diffuses through extracellular fluid.

  • Example: Electrical signals in nerve cells trigger release of neurotransmitters that cross the synapse to stimulate target cells.

Long-Distance Signaling

  • Definition: Communication between cells located far apart.

  • Hormones: Messenger molecules that travel through tissues and the bloodstream to reach target cells.

    • Mechanism: Endocrine cells release hormones into blood vessels, where they bind specifically to target cells.

Signal Transduction Pathways

  • Overview: Convert external signals into internal responses, includes three main steps.

Step 1: Reception

  • Process: Ligand (signal molecule) binds to receptor protein, causing a conformational change.

    • Specificity: The cell's ability to respond relies on having the correct receptor.

  • Receptor Types: Most are plasma membrane proteins, such as G protein-coupled receptors.

Step 2: Transduction

  • Mechanism: Ligand binding activates a cascade of molecular reactions.

    • Includes phosphorylation and dephosphorylation events.

    • Benefits: Amplifies signals and improves coordination/regulation.

  • Scaffolding Proteins: Large proteins increasing efficiency by grouping relay proteins involved in the same pathway.

  • Second Messengers: Small, non-protein molecules spread through the cell, examples include cyclic AMP and calcium ions.

Step 3: Response

  • Actions: Leads to final cellular responses such as opening ion channels or activating transcription factors that turn on genes.

Specificity and Coordination

  • Uniqueness of Responses: Different cells have different protein collections, leading to diverse responses to the same signal.

    • Allows for branching (multiple responses) and cross-talk between signaling pathways.

Termination of the Signal

  • Inactivation Mechanisms: Essential for cell signaling.

  • Apoptosis: Programmed cell death triggered by factors like DNA damage.

    • Malfunctioning apoptosis responses are linked with cancer progression.