Cell Membrane Structure and Function Quiz

Cell Membrane: Gatekeeper

• Functions: Regulates what enters and exits the cell, maintains homeostasis, essential for all cells
• Structure: Known as the fluid mosaic model, composed of phospholipids, proteins, and cholesterol

Phospholipid Bilayer

• Two layers of phospholipids: Hydrophilic (polar) heads face outwards towards the watery environment, while hydrophobic (nonpolar) tails point inwards, creating a barrier
• Fluid nature: Molecules in the cell membrane are not fixed, they can move freely, allowing for flexibility

Proteins in the Cell Membrane

• Integral proteins: Permanently embedded in the membrane, some span the entire membrane (transmembrane proteins)
• Peripheral proteins: Adhere temporarily to one side of the membrane
• Types of proteins and their functions:
  • Transport proteins/ion channels: facilitate movement of molecules across the membrane
  • Anchor proteins: attach to other structures, providing stability
  • Receptor proteins: bind to signaling molecules, triggering cellular responses
  • Enzymes: catalyze reactions
  • Glycoproteins: have sugar "nametags" for cell identification, examples include blood types

Cholesterol's Role

• Stability and movement: Cholesterol keeps the cell membrane from becoming too solid or too fluid, ensuring efficient functioning

Selectively Permeable Membrane

• Allows: Small, nonpolar molecules like oxygen, carbon dioxide, and water (but slowly due to its polarity)
• Doesn't allow: Large molecules, charged molecules (ions), and polar molecules (e.g., glucose)
• Important molecules that can't pass directly: Amino acids, carbohydrates, ions

Movement Across the Cell Membrane

• Passive transport: No energy required
  • Diffusion: Movement from high concentration to low concentration
  • Facilitated diffusion: Uses transport proteins for molecule movement, still passive
  • Osmosis: Diffusion of water across a selectively permeable membrane
• Active transport: Requires energy (ATP)
  • Moves molecules from low concentration to high concentration
  • Uses carrier proteins

Osmosis

• Hypertonic solution: Higher solute concentration than the cell, water moves out of the cell
• Isotonic solution: Equal solute concentration as the cell, no net movement of water
• Hypotonic solution: Lower solute concentration than the cell, water moves into the cell

Effects of Osmosis on Cells

• Animal cells:
  • Hypertonic: Shrinking, shriveling
  • Isotonic: Normal
  • Hypotonic: Swelling, lysis (bursting)
• Plant cells:
  • Hypertonic: Plasmolysis (cell membrane pulls away from cell wall)
  • Isotonic: Flaccid (limp)
  • Hypotonic: Turgid (normal, firm)

Dynamic Equilibrium

• Continues movement of water across the membrane, but no net change in overall concentration

Active Transport

• Requires energy (ATP): To move molecules against their concentration gradient
• Carrier proteins: Aid in the specific transport of certain molecules

Exocytosis and Endocytosis

• Exocytosis: Release of molecules outside the cell through fusion of a vesicle with the plasma membrane
• Endocytosis: Taking in molecules inside the cell by forming a pouch that pinches off as a vesicle
  • Phagocytosis: "Cell eating", engulfing large particles
  • Pinocytosis: "Cell drinking", taking in fluids and dissolved materials

Test your understanding of the cell membrane's structure and its essential functions in regulating cell behavior. Explore key concepts like the fluid mosaic model, phospholipid bilayer, and various proteins involved. This quiz will help reinforce your knowledge of cellular biology.