Chapter_5_Plasma_Membrane__1_

Chapter 5: Structure and Function of Plasma Membranes

Components and Structure

  • Plasma Membrane: Essential barrier surrounding cells, integral for maintaining homeostasis.

Learning Objectives

  • Characteristics of a Plasma Membrane:

    • Fluid mosaic model provides a framework for understanding membrane structure.

  • Components of a Plasma Membrane:

    • Function: Controls movement of substances in and out of cells.

    • Location: Encloses the cell's cytoplasm.

    • Specific Cell Types: Varies among diverse organisms.

  • Sketch a Cell Membrane:

    • Include phospholipids, cholesterol, integral proteins, peripheral proteins.

  • Membrane Asymmetry:

    • Different lipid and protein compositions on each side of the membrane.

  • Selectively Permeable:

    • Membranes allow certain substances to pass while restricting others.

    • Factors affecting fluidity include lipid composition, temperature, and presence of cholesterol.

  • Characteristics of Easily Permeable Molecules:

    • Small, non-polar molecules cross the membrane easily.

  • Comparison of Transport Types:

    • Passive transport (does not require energy) vs Active transport (requires energy).

Key Terms

  • Plasma Membrane: Semi-permeable barrier.

  • Selectively Permeability: Ability to control substance passage.

  • Phospholipid: Fundamental building block.

  • Integral Proteins: Embedded in the lipid bilayer.

  • Peripheral Proteins: Loosely attached to the membrane surface.

  • Glycoproteins/Glycolipids: Involved in cell recognition.

  • Endomembrane System: Network of membranes within the cell.

  • Passive Transport: Movement across the membrane without energy.

  • Active Transport: Movement requiring energy, moving substances against their gradient.

Phospholipid Structure

  • Structure: Composed of hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.

    • Contributes to the membrane's polarity and dual nature.

Functions of the Plasma Membrane

  • Structural Support: Maintains cell shape and integrity.

  • Selective Permeability: Governs substance transport.

  • Cell Communication: Facilitates signaling between cells.

  • Cell Adhesion: Holds cells together.

  • Cell Recognition: Identifies cellular identity aids in immune response.

Components of the Plasma Membrane

  • Phospholipids: Form lipid bilayer.

  • Proteins: Perform various functions, including transport.

  • Carbohydrates: Often attached to proteins/lipids for recognition.

  • Cholesterol: Stabilizes membrane fluidity.

Fluid Mosaic Model

  • Concept: The membrane is viewed as a fluid structure with diverse proteins embedded.

Factors Affecting Fluidity

  • Temperature: Warmer temperatures increase fluidity.

  • Cholesterol: At high temperatures, it stabilizes; at low temperatures, it prevents solidification.

  • Saturation of Fatty Acids: More unsaturated fats increase fluidity due to kinks in the chains.

Selective Permeability:

  • Definition: Membrane's ability to regulate what enters/exits.

  • Causes: Depends on polarity, size, and concentration gradient of molecules.

Molecule Types

  • 1. Ions: Charged particles that generally cannot cross the membrane easily.

  • 2. Large polar molecules: Typically require assistance to cross.

  • 3. Small non-polar molecules: Easily cross due to their size and charge properties.

Types of Transport Across the Plasma Membrane

  • Passive Transport: Includes diffusion and facilitated diffusion that do not require energy.

  • Active Transport: Requires energy to move substances against their gradients.

Transport Proteins

  • Carrier Proteins: Assist in moving molecules across the membrane.

  • Three types of Transporters: Integral membrane proteins functioning in transport processes.

Passive Transport

Part 2

  • Learning Objectives: Explain passive transport and its types, including simple diffusion and facilitated diffusion.

  • Osmosis: The special case involving water movement across membranes.

  • Compare Tonicity: Understanding solutions in relation to osmotic effects on cells.

Key Terms

  • Diffusion: Movement of molecules from high to low concentration.

  • Facilitated Diffusion: Requires specific carrier proteins.

  • Osmosis: Water movement across a semi-permeable membrane.

  • Tonicity: The ability of a solution to affect cell volume by osmosis.

Passive Transport Overview

  • Factors influencing diffusion include temperature, concentration gradient, and particle size.

Osmotic Pressure

  • Understanding the pressures created by water movement, influencing turgor pressure in cells.

Tonicity Understanding

  • Turgor Pressure: The pressure exerted by the fluid in the vacuole against the cell wall, crucial for plant cell structure.

Active Transport

Part 3

  • Learning Objectives: Understand electrochemical gradients and energy requirements for active transport.

  • Sodium-Potassium Pump: A key example of primary active transport.

  • Types of Active Transport: Primary vs. Secondary, involving direct energy use and energy derived from gradients.

Bulk Transport

Part 4

  • Learning Objectives: Differentiate between endocytosis and exocytosis, including the three types of endocytosis — phagocytosis, pinocytosis, and receptor-mediated endocytosis.

    • Key Terms: Endocytosis (intake) and Exocytosis (release) involving vesicles to transport large particles.