Recording-2025-03-10T10:56:25.905Z

Introduction

• Overview of the lecture divided into five sections covering:

  • Major parts of a cell

  • Functions of membrane proteins

  • Processes of active and passive transport

Extracellular Environment

• Extracellular Fluid:

  • Dynamic medium surrounding cells, primarily composed of water.

  • Contains the extracellular matrix (ECM), which can exist in solid or gel-like forms based on tissue type.

Plasma Membrane

• Definition:

  • Outermost boundary of the cell; acts as a protective shield.

• Selective Permeability:

  • Preserves cell integrity; regulates movement of substances, acting as a gatekeeper for essential molecules.

  • Facilitates communication between the cell and its surroundings.

• Cytoplasm:

  • Interior region containing structures, molecules, and organelles, excluding the nucleus.

  • Supports cell functions and maintains internal environment.

  • Plasma membrane ensures selective passage of materials to and from the cytoplasm.

Composition of the Plasma Membrane

• Phospholipid Bilayer:

  • Core structure consists of two layers of phospholipid molecules.

• Cholesterol and Proteins:

  • Integral components that provide structural integrity and functionality to the membrane.

Types of Membrane Proteins

• Structural Proteins:

  • Connect cells to neighboring cells and the extracellular matrix; extend into the cytoskeleton.

• Channel Proteins:

  • Hollow pores allowing water and charged particles to pass through; essential for substance transport across the membrane.

  • Example: Aquaporins allow selective water movement while restricting hydrogen ions.

• Glycoproteins:

  • Proteins with carbohydrate groups that help in cell recognition and binding to extracellular substances.

  • Form a glycocalyx layer that assists the immune system in distinguishing between self and non-self.

Membrane Transport

• Passive Transport:

  • No energy required; substances move from high to low concentration (diffusion).

  • Example: Food coloring diffusing in water; channel proteins facilitate movement (e.g., aquaporins for water).

  • Gases: Oxygen and carbon dioxide can diffuse freely across the membrane.

  • Some cells utilize passive transport for glucose uptake.

• Active Transport:

  • Requires energy to move substances against their concentration gradient (low to high).

  • Examples: Sodium ions are pumped out while potassium ions are pumped in by the sodium-potassium pump, utilizing ATP for energy.

Cytoskeleton

• Definition:

  • Network of proteins that defines cell shape and provides mechanical strength.

  • Capable of reorganizing for cell shape alteration and migration.

Components of the Cytoskeleton

• Microfilaments:

  • Thinnest fibers composed of actin, involved in cell movement and contraction.

• Intermediate Filaments:

  • Composed of keratin, provide strength and structural integrity.

• Microtubules:

  • Largest fibers made of tubulin, organize chromosomes during cell division.

  • Important for maintaining cell shape and function.

Cellular Extensions

• Microvilli:

  • Finger-like projections that increase cell surface area for absorption and interaction with the environment.

• Cilia:

  • Longer, hair-like projections that actively move fluids or mucus across the cell surface (e.g., mucus clearance in lungs, egg propulsion in reproduction).

• Centrioles:

  • Pair of structures near the nucleus that guide chromosome movement during cell division.