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.