Cell Signaling

Cell Signaling Overview

Introduction to Cell Signaling

  • Importance of cell communication discussed through pair-sharing questions:

    • Key Question: Why is it important for cells to communicate with each other?

Pathway Diagram Analysis

  • Purpose of Pathway Diagrams: Illustrate chemical or signaling pathways and derive crucial information:

    1. Activators: Proteins, enzymes, and molecules that activate the pathway.

    2. Inhibitors: Proteins, enzymes, and molecules that inhibit the pathway.

    3. Gene Regulation: Indicates whether transcription of a gene is induced or repressed.

    4. Second Messengers: Identifies molecules acting as second messengers in cell signaling pathways.

  • Key Questions Analyzed:
    A. p53 Function:

    • p53 leads to inhibition of the cell cycle.
      B. MDM2 Function:

    • MDM2 inhibits p53, allowing initiation of the cell cycle.
      C. Effect of DNA Damage:

    • DNA damage inhibits MDM2, activating p53 and inhibiting the cell cycle.

  • Signaling Pathway Symbols:

    • Inhibition: Denotes the suppression of a molecule or process.

    • Activation: Denotes the enhancement of a molecule or process.

Topic 4.1: Cell Communication

  • Learning Objectives:

    • IST-3.A: Describe cell communication methods.

    • IST-3.B: Explain communication over short and long distances.

What is Cell Signaling?

  • A series of steps allowing cells to respond to environmental signals.

    • Response initiated through some cellular activity (e.g., initiation of the cell cycle).

    • Ligand Secretion: Chemical signals secreted from the initiating cell to the target cell.

    • Receptor Protein Requirement: Only target cells with the correct receptor will respond to the signal.

Steps in Cell Signaling Process

  1. Reception:

    • Ligand binds to the receptor protein, causing a conformational (shape) change.

  2. Transduction:

    • Signal transference from cell membrane to nucleus via phosphorylation of proteins.

    • Phosphorylation: The addition of phosphate groups to proteins.

  3. Response:

    • Final molecule in the signal pathway initiates transcription of target genes in the nucleus, leading to protein production causing a cellular response.

Topic 4.2: Reception and Transduction Basics

  • Learning Objectives:

    • IST-3.C: Describe components of a signal transduction pathway.

    • IST-3.D: Explain the role of components in producing cellular responses.

Mechanisms of Cell Communication

Paracrine Signaling

  • Physical contact between cells to transmit signals that initiate responses.

  • Requires direct contact between signaling and receptor proteins on cell membranes.

  • Ligands can diffuse short distances or travel long distances through the bloodstream.

Cell to Cell Contact Mechanisms

  • Gap Junctions:

    • Found in animal cells; cell membranes fuse and form pores for rapid signal diffusion.

  • Plasmodesmata:

    • Specific to plant cells; pores open between cell membranes and cell walls for signaling.

  • Fastest means of transmitting signals through direct contact.

Traditional Cell-Cell Contact

  • The originating cell expresses a ligand on the cell membrane, which binds to a receptor on the target cell.

Topic 4.3: Cell Response to Transduction

  • Learning Objectives:

    • IST-3.E: Describe the environment's role in cellular responses.

    • IST-3.F: Describe different types of cellular responses to signal transduction pathways.

Cellular Responses to Signal Transduction

  • Signaling mechanisms enable cells to respond to their environments.

  • Transduction pathways lead to transcription of target genes and subsequent protein production, resulting in appropriate cell response.

Examples of Cell Responses

  • Initiation of gene expression (protein synthesis).

  • Inducing cell growth and entry into the cell cycle.

  • Stimulating secretion of molecules.

  • Initiating programmed cell death (apoptosis).

Topic 4.4: Changes in Signal Transduction Pathways

  • Learning Objectives:

    • IST-3.G: Explain how changes in signaling molecule structures affect pathway activity.

Impact of Structural Changes in Signaling Molecules

  • Mutations leading to shape and chemical affinity changes in signaling or receptor molecules can disrupt or halt normal cell responses.

Interference by Chemical Compounds

  • Many medicines and toxins influence signaling pathways by activating or inhibiting them.

    • Example: Botulinum Toxin (Botox):

      • Breaks down SNARE proteins required for neurotransmitter release, leading to muscle paralysis.

Topic 4.5: Feedback Mechanisms

  • Learning Objectives:

    • ENE 3A: Describe feedback mechanisms.

    • ENE 3B: Explain negative feedback's role in maintaining homeostasis.

    • ENE 3C: Explain positive feedback's effect on homeostasis.

Feedback Mechanisms Overview

  • Sensory pathways and responses maintain homeostasis through:

    1. Negative Feedback: Slows or halts responses to maintain stability.

    2. Positive Feedback: Amplifies responses to generate large systemic changes to restore homeostasis.

Differentiation of Feedback Mechanisms

  • Negative Feedback Mechanism:

    • Regulates physiological processes by stopping cellular responses, aiding the return to normal state (homeostasis).

  • Positive Feedback Mechanism:

    • Enhances or initiates biological processes for systemic changes needed to re-establish homeostasis.

Negative Feedback Examples

  • Inhibiting enzyme 3 leads to the accumulation of substrate B because it cannot convert to intermediate C.

  • Inhibiting enzyme 5 results in substrate D accumulation due to its failure to convert into isoleucine.

Any Questions?

  • Students can contact Deschamps for clarifications.