4-Chapter 10 Lecture

Chapter 10 – Cell and Tissue Form

  • Lecture by Dr. Richard Quintana Feliciano

  • Text Reference: Morris, How Life Works, 4e, Macmillan Higher Education, 2022

Covered Core Concepts

10.2 The Cytoskeleton

  • Composed of microfilaments, intermediate filaments, and microtubules.

  • Functions to maintain cell shape.

10.3 Cell Junctions

  • Connects cells to one another to form tissues.

The Cytoskeleton

Definition and Structure

  • Determines and maintains cell shape through structural protein networks.

  • Consists of three main components:

    • Microfilaments

    • Intermediate Filaments

    • Microtubules

  • Collaborates with cell junctions and the extracellular matrix to ensure tissue and organ integrity.

Evolutionary Perspective

  • The structure and function of the cytoskeleton have remained relatively unchanged throughout evolution.

  • Prokaryotes possess similar protein systems to eukaryotic cytoskeletal elements.

Functions

  • Provides internal structural support.

  • Facilitates the movement of substances within cells.

  • Formed from long chains of protein subunits; eukaryotes notably have microtubules and microfilaments, while animal cells have intermediate filaments.

Microtubules

Structure

  • Formed from tubulin dimers (α and β tubulin).

  • Microtubules radiate from centrosomes, preventing cellular compression.

  • Arranges and tethers many cellular organelles.

Dynamic Behavior

  • Microtubules experience growth at the plus end; shrinkage occurs rapidly at the minus end, known as dynamic instability.

  • Important during cell division for chromosome segregation.

Microfilaments

Structure and Function

  • Comprise actin polymers in a helical configuration.

  • Positioned under the cell membrane, they help reinforce and organize membrane-associated proteins.

Specific Roles

  • Form microvilli in epithelial cells of the small intestine, providing structural support.

  • Involved in the transport of materials, muscle contraction, and cytokinesis during cell division.

Interaction with Motor Proteins

Myosin

  • Microfilaments interact with myosin to enable movement, shape changes, and transport within cells.

  • Muscle cells utilize myosin to contract and generate force.

Intermediate Filaments

Composition and Function

  • Made of various proteins depending on cell type (e.g., keratins in epithelial cells).

  • Provide mechanical strength and stability to cells.

  • Important for maintaining the integrity of tissues during stress.

Cell Junctions Overview

Types and Functions

  • Tight Junctions: Prevent passage of materials; segment cell membranes.

  • Desmosomes: Button-like adhesion points that strengthen connections via intermediate filaments.

  • Adherens Junctions: Cadherins form a belt-like structure connecting to microfilaments.

  • Gap Junctions: Allow communication between cells via ions and molecules, made up of integral membrane proteins.

  • Plasmodesmata: Similar to gap junctions but in plant cells; allow transport across cell walls.

Importance of Cell Junctions

  • Hold tissues together, allowing them to function as a unit.

  • Facilitate communication between adjacent cells through various adhesion molecules, primarily cadherins and integrins.

Core Concepts Summary

Cytoskeletal Features

  • Microfilaments, intermediate filaments, and microtubules play crucial roles in determining cell shape and facilitating movement.

  • Dynamic nature allows for rapid assembly/disassembly, essential for various cellular functions.

Cell Junction Functions

  • Junctions ensure cells are anchored to one another and to the extracellular matrix, allowing for structural integrity and communication.