Lecture Notes: Cell Membrane

Overview

• Cell Membrane / Plasma Membrane: Terms are interchangeable.
• Functions as a separator and communicator between the inside and outside of cells.

Key Functions of the Cell Membrane

1. Separation:
   • Separates internal cell environment from external.
   • Critical for both unicellular (e.g., prokaryotic) and multicellular organisms.
   • Separates from other cells and interstitial spaces in multicellular organisms.
2. Permeability:
   • Allows certain substances to pass through while blocking others.
   • Movement can be facilitated or restricted.
3. Communication:
   • Cells communicate for coordinated functions (e.g., heart cells contracting).
   • Involves signaling molecules like hormones.
4. Connection:
   • Cells connect tightly (e.g., in heart and digestive systems) preventing leaks.

Structural Components

• Phospholipid Bilayer:
  • Primary structure of the cell membrane.
  • Composed of lipids with hydrophilic heads and hydrophobic tails.
  • Creates a barrier with the heads facing water (inside and outside of cells).
• Proteins:
  • Embedded within the bilayer.
  • Varied functions including transport, communication, and recognition.
• Cholesterol:
  • Stabilizes cell membrane structure.
  • Maintains membrane fluidity.

Fluid Mosaic Model

• Describes the cell membrane as a dynamic combination of lipids, proteins, and other molecules.
• Reflects flexibility and varied composition, resembling a mosaic.

Types of Proteins in the Membrane

1. Transport Proteins:

   • Move hydrophilic molecules across the membrane.
   • Types include channel proteins and carrier proteins.
   • Channel Proteins: Form pores for specific ions based on size and polarity.
   • Carrier Proteins: Change shape to transport specific molecules.

2. Receptor Proteins:

   • Facilitate large cellular events (e.g., hormone binding leading to puberty).
   • Can trigger significant cellular responses.

3. Enzymes:

   • Catalyze chemical reactions, reducing energy requirements.
   • Located throughout the cell, including the membrane.

4. Recognition Proteins (Glycoproteins):

   • Identify cell types, important for immune response.
   • Provide cellular information (e.g., blood type identifiers).

5. Connection Proteins:

   • Anchor cells to each other and to the extracellular matrix.

Cholesterol's Role

• Stabilizes membrane fluidity and structure.
• Important for cell membrane function, though balance is key.

Summary

• Lipids: Responsible for isolating function.
• Proteins: Regulate exchange and communication.

These notes summarize the lecture's discussion on the structure and function of the cell membrane, emphasizing its components and their roles in maintaining cellular integrity and function.