Cell to Cell Communication

Exam Overview

  • Upcoming topics regarding common mistakes from previous exam.

  • Discussion of study tips for future exams.

  • Mention of the brevity of the lecture compared to previous ones.

Exam Scores and Common Mistakes

  • Exam 3 scores will be posted tomorrow (Friday).

  • Common mistakes noted include:

    • Misunderstanding of E3 ubiquitin ligases and their specificity.

    • Questions about lysosomal components.

Detailed Explanation of Key Concepts

E3 Ubiquitin Ligases

  • Discussed the role of E3 ubiquitin ligases in cellular waste management.

  • Sequential Specificity:

    • E1 ubiquitin ligase has fewer specificities, while E3 has the most.

    • How E3 ligases bind to multiple proteins to maintain specificity and prevent unwanted breakdown.

Lysosomes

  • Key lysosomal membrane embedded structures:

    • Metabolite Transporter: Responsible for recycling parts by breaking down compounds and redistributing them to the cell.

    • Proton Pump: Maintains acidity within lysosomes by pumping protons to facilitate enzyme function.

Cell Signaling and Transcription

  • Discussion on Wnt signaling pathway and its implications in cancer:

    • Role of Wnt in allowing beta-catenin to participate in transcription.

    • Importance of APC in degrading beta-catenin when Wnt signaling is inactive.

  • Mutations in APC lead to continuous activation of beta-catenin, resulting in uncontrolled proliferation and cancer development.

GPCR (G-Protein Coupled Receptors)

  • Structure and Function:

    • GPCRs are seven transmembrane receptors that activate heterotrimeric G proteins.

    • Upon activation, GPCR releases GDP and binds GTP, leading to further signaling.

  • Formation of secondary messengers:

    • Activation of adenylyl cyclase, leading to production of cyclic AMP (cAMP).

    • cAMP can activate protein kinase A (PKA), leading to direct protein action or transcription response.

  • Comparison of speed of responses:

    • Faster response at protein level vs. slower response at transcription level (transcription involves multiple steps: synthesis, translation, and potential post-translational modifications).

Feedback Mechanisms

  • Explanation of positive and negative feedback in signaling pathways:

    • Positive Feedback:

    • Downstream activators sustain the pathway to ensure proper cellular differentiation, especially in stem cells.

    • Negative Feedback:

    • Mechanisms to stop activation once a certain threshold is reached (e.g., downregulation, inactivation, or destruction of receptors).

  • Mention of the endosomal system's role in feedback and receptor cycling.

Study Tips for Lectures

  • How to condense information from complex lectures:

    • Focus on connections between cells, types of cells, and their structural features.

    • Importance of specific tissues (brain, skin, heart, pancreas, intestines) and cellular arrangements.

  • Understanding types of epithelial cells (columnar, squamous, cuboidal, stratified) and their characteristics.

Epithelial Cells and Organization

  • Epithelial cells have distinct polarities:

    • Apical surface (top) vs. Basal surface (bottom).

    • Importance of maintaining these orientations for proper function.

    • Examples of epithelial variations in the gut and their structural implications.

Cell Junctions and Communication

Common Features of Cell Junctions

  • Essential components in cell junctions:

    • Cytoskeletal Filaments: Structural support of the cell.

    • Adapter Proteins: Connect adhesion proteins to cytoskeletal components.

    • Adhesion Proteins: Mediate binding between cells or cell-ECM connections.

Extracellular Matrix (ECM)

  • Overview of significant ECM components:

    • Proteoglycans: Large molecules that cushion and mediate hydration in the ECM.

    • Elastin: Provides elasticity and mechanical support.

    • Collagen: Most abundant protein, providing structural strength and resistance to tensile forces.

    • Fibronectin: Acts as an adapter connecting integrins (adhering proteins) to ECM.

Types of Junctions

Microfilament Junctions

  • Adherens Junctions:

    • Use cadherins for cell-cell connections, coordinating shape changes.

    • Act as mechanosensors in certain tissues like the gut.

  • Focal Adhesions:

    • Connect ECM to cells using integrins, crucial for wound healing.

Intermediate Filament Junctions

  • Desmosomes:

    • Cell-cell connections that distribute mechanical stress using desmoglein and desmocolin cadherins.

  • Hemidesmosomes:

    • Connect cells to the ECM using integrins, anchoring cells.

Coordinating Junctions

  • Tight Junctions:

    • Seal adjacent cells in a layer, preventing leaks and maintaining separation of fluids and solutes.

    • Important in the gut and blood-brain barrier.

  • Gap Junctions:

    • Permit direct communication between neighboring cells through connexins, allowing ions and small molecules to pass, facilitating synchronization and coordination.

Key Takeaways

  • Importance of structural integrity and communication in cellular organization across different tissues.

  • Various junction types allow for specialized functions based on tissue requirements.

  • Recognition of how cell signaling pathways and junction types interplay in health and disease.