General Biology 01: Cell Membrane and Transport

Cell Membrane Overview

• All prokaryotic and eukaryotic cells are surrounded by a cell membrane, serving as a selective barrier.
• The cell membrane regulates the movement of substances, protecting cellular components and maintaining homeostasis.

Functions of the Cell Membrane

• Selective Permeability: Controls substance entry and exit, critical for cell survival and function.
• Cell Identification: Distinguishes cells from one another through specific markers.
• Intercellular Signaling: Participates in cell communication and signaling processes.

Fluid Mosaic Model

• Proposed by S.J. Singer and Garth L. Nicolson in 1972, represents cell membranes as dynamic and flexible structures.
• Fluid Component: The phospholipid bilayer allows lateral movement of phospholipids.
• Mosaic Component: Proteins embedded in the bilayer create a diverse array of components.

Structure and Composition

• The lipid bilayer consists of phospholipids, cholesterol, and glycolipids, forming a resilient barrier around the cytoplasm.

Signal Transduction

• Cell-surface receptors interact with signaling molecules (e.g., hormones), leading to cellular responses through protein shape changes.

Cell-Cell Recognition

• Glycoproteins and glycolipids act as identification markers, facilitating recognition and response to foreign cells.

Intercellular Joining

• Integral proteins function as linkers, anchoring adjacent cells together and contributing to tissue structure.

Gradient Across the Cell Membrane

• A concentration gradient refers to the increase or decrease of chemical density across a membrane, influencing substance movement.
• Molecule characteristics affecting membrane transport: size, charge, and solubility.

Transport Mechanisms

• Cellular Transport: Involves the movement of substances in and out of the cell via various mechanisms.

Channel-Mediated Facilitated Diffusion

• Utilizes ion channels to allow specific ions (e.g., K+) to pass through the membrane.

Carrier-Mediated Facilitated Diffusion

• Carrier proteins bind to molecules (e.g., glucose), changing shape to transport them across the membrane.

Osmosis

• Special diffusion of water across a selectively permeable membrane, aiming for equilibrium; involves pressures and concentration differences.

Tonicity

• Defines the concentration strength of a solution relative to cells, affecting cell behavior.
• Hypotonic: More water outside; cells may lyse due to water influx.
• Hypertonic: Less water outside; cells may crenate from water loss.
• Isotonic: Equal concentration; no net water movement occurs.

Active Transport

• Movement of molecules against their concentration gradient requires energy.
• Primary Active Transport: Uses ATP to transport substances across the membrane.
• Secondary Active Transport: Utilizes ion concentration gradients to move other substances.

Transport in Vesicles

• Endocytosis: Mechanism for large molecules to enter cells; membrane invaginates to form vesicles.
  • Phagocytosis: “Cell eating” of large solids.
  • Pinocytosis: “Cell drinking” of fluids and solutes.
  • Receptor-Mediated Endocytosis: Specific uptake of ligands via receptor interactions.
• Exocytosis: Process for exporting materials; vesicles fuse with the plasma membrane to release contents outside the cell.

Clinical Connections

• Body cells require isotonic environments; hypertonic or hypotonic solutions can damage cells.
• IV solutions are typically isotonic; hypertonic solutions can aid in treating conditions like cerebral edema. Hypotonic solutions can help rehydrate dehydrated cells.

Explore the intricate world of cell membranes and their transport mechanisms in this General Biology 01 quiz. Learn about the structural components and functions of the cell membrane while examining the relationship between cell structure and membrane function.