Plasma Membrane Dyna mics

Plasma Membrane Dynamics

• Course: BIOL 2610: Human Anatomy and Physiology I

Learning Objectives

• Structure and Functions of Plasma Membrane:

  • Describe its components and purposes.

• Membrane Proteins:

  • List and define the functions of the four types of membrane proteins.

• Transport Mechanisms:

  • Characteristics of channels and carriers.

  • Types of membrane transport processes.

  • Transepithelial transport mechanisms.

• Distribution of Body Fluids:

  • Understand osmolarity and tonicity of solutions.

Components of the Cell

• Key Components:

  • Plasma membrane

  • Cytoplasm

    • Cytoskeleton

    • Organelles

    • Inclusions

    • Cytosol

Structure of the Plasma Membrane

• Functions:

  • Acts as a physical barrier between intracellular and extracellular environments.

  • Facilitates communication between cells and external environment.

  • Provides structural support and regulates substance movement.

• Composition:

  • Lipid Bilayer:

    • Consists of two layers of phospholipids.

    • Embedded proteins, some anchored, others mobile.

    • Cholesterol molecules found among phospholipids, contributing to fluidity.

    • Carbohydrates on the outer surface form glycoproteins and glycolipids.

Fluid Mosaic Model of Plasma Membrane

• Description:

  • A dynamic model describing phospholipids and membrane proteins arrangement into a mosaic pattern.

  • Active membranes contain a higher number of proteins, associated with increased metabolism.

• Permeability:

  • Permeable to lipid-soluble molecules such as O2, CO2, and small lipids.

  • Use of channel proteins for ions and water movement.

  • Carrier proteins for larger molecules like glucose and amino acids.

Glycocalyx

• Functionality:

  • Forms a protective sugar coating around the cell.

  • Plays a role in structural stability, recognition, and cell signaling.

Membrane Proteins

• Types of Membrane Proteins:

  • Integral Proteins:

    • Span entire plasma membrane and disrupt membrane structure if removed.

  • Peripheral Proteins:

    • Attach loosely to membrane surfaces and can be removed without affecting the membrane.

  • Lipid-Anchored Proteins:

    • Covalently bonded to lipid tails embedded within the bilayer.

• Functions:

  • Structural: Maintain cell shape and form cell junctions.

  • Enzymatic: Catalyze chemical reactions on cell surfaces.

  • Receptors: Trigger cellular responses by binding specific ligands.

  • Transporters: Facilitate the movement of substances across the membrane.

Transport Mechanisms

• Types of Membrane Transport:

  • Passive Transport:

    • Does not require energy (e.g., diffusion, osmosis).

  • Active Transport:

    • Requires ATP to move substances against concentration gradients.

• Facilitated Diffusion:

  • Passive movement down concentration gradients via specific carrier proteins; reaches equilibrium when concentrations equalize.

• Endocytosis and Exocytosis:

  • Endocytosis: Process by which cells engulf substances.

    • Types include phagocytosis (cell eating) and pinocytosis (cell drinking).

  • Exocytosis: Transportation of materials out of the cell via vesicles.

• Transepithelial Transport:

  • Movement of substances across epithelial cells involves both active and passive transport mechanisms. Each epithelial cell has distinct apical and basolateral membranes with varying transport proteins.

Water Distribution and Solute Dynamics

• Water Content:

  • Represents a significant portion of body weight, with intracellular fluid comprising about 67% and extracellular fluid 33%.

• Osmolarity and Tonicity:

  • Osmolarity: The total concentration of solute particles in a solution.

  • Tonicity: Effect of a solution on cell volume (hypotonic, hypertonic, isotonic).

• Osmotic Pressure:

  • Water movement across semipermeable membranes is influenced by solute concentrations, with water moving to equilibrate solute concentrations.

• Chemical Equilibrium:

  • Occurs when concentrations are balanced across membranes.

  • Disequilibrium persists due to constant energy input, maintaining concentration gradients crucial for physiological functions.

Summary Points on Membrane Transport Mechanisms

• Simple Diffusion: Movement from high to low concentration, needing no energy.

• Facilitated Diffusion: Requires carrier proteins to move substances across membranes without energy, reaching equilibrium.

• Active Transport (Primary and Secondary): Utilizes ATP to move substances against concentration gradients; secondary transport relies on energy from primary gradients.

• Vesicular Transport: Engages in transporting large particles or volumes of substances using vesicles; ATP is often required.