Cell Membrane Structure and Function Quiz

Glycocalyx

• Composed of carbohydrate side chains from glycoproteins and glycolipids.
• Forms a fuzzy material on the outer surface of cell membranes.
• Thickness is approximately 50 nm.
• Contains polar oligosaccharide chains covalently linked to proteins and some lipids.

Membrane Proteins

• Integral Proteins: Known as transmembrane proteins, they function as membrane receptors and transport proteins.
• Peripheral Proteins: Do not penetrate the lipid bilayer; usually found on the cytoplasmic side, involved in cytoskeleton scaffolding or intracellular signaling.

Plasma Membrane Transport Processes

• Passive Transport: Does not require energy; substances move from higher to lower concentration.

  • Simple Diffusion: Movement of small non-polar (O2, N2) and small polar molecules (H2O, CO2, Glycerol) based on concentration gradient.
  • Facilitated Diffusion: Utilizes ion channels and carrier proteins, demonstrating specificity for particular molecules.
    • Ion Channels: Multi-pass transmembrane proteins that form pores for specific ions to passively flow through the membrane.
    • Carrier Proteins: Transmembrane proteins that change shape to facilitate the movement of specific molecules; can function in both passive and active transport.
  • Osmosis: The diffusion of water through a selectively permeable membrane, guided by solute concentrations until equilibrium occurs.

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

  • Na+-K+ Pump: Carrier protein (ATPase) facilitating the antiport of sodium and potassium ions.
  • Glucose Transport: Symport mechanism for moving glucose across epithelial layers.

• Vesicular Transport: Involves vesicle formation to transport materials into and out of cells.

  • Exocytosis: Bulk expulsion of substances by fusion of vesicles with the plasma membrane.
  • Endocytosis: Bulk intake of substances via vesicle formation at the plasma membrane.
    • Phagocytosis: Engulfing of large particles or cells (“cell eating”).
    • Pinocytosis: Uptake of interstitial fluid and solutes (“cell drinking”).
    • Receptor-mediated Endocytosis: Specific binding of substances followed by vesicle formation for uptake.

Cytoplasm

• Comprised of three main structural components:
  • Organelles
  • Inclusions
  • Elementary Particles (e.g., ATP synthase)

Organelles

• Mitochondria: May originate from anaerobic eukaryotic cells engulfing aerobic microorganisms, responsible for oxidative energy processes. Proliferate by fission; typical lifespan is about 10 days.

• Golgi Complex: Stack of membrane-bound cisternae engaged in modifying, sorting, and packaging proteins.

  • Cis Face: Faces the endoplasmic reticulum, also known as the cis Golgi network.
  • Medial Compartment: Region between the cis and trans faces.
  • Trans Face: Faces vacuoles/secretory granules, contains the trans Golgi network for protein sorting.

• Lysosomes: Membrane-bound organelles containing acidic hydrolases for degrading materials.

  • Types of Lysosomes:
    • Multivesicular Bodies: Fusion of early endosomes with late endosomes.
    • Phagolysosomes: Fusion of phagocytic vacuoles with lysosomes.
    • Autophagolysosomes: Formed by fusing autophagic vacuoles with lysosomes.
    • Residual Bodies: Contain undegradable material after lysosomal function is exhausted.

• Peroxisomes: Membrane-bound organelles rich in enzymes for oxidizing fatty acids and detoxifying substances like ethanol. Contain catalase for breaking down hydrogen peroxide.

Inclusions

• Contain various cellular components like:
  • Glycogen
  • Lipid Droplets
  • Lipofuscin
  • Centrosomes: Major microtubule organizing centers crucial for cell division.

Cytoskeleton

• Serves as a structural framework within the cytosol.
• Functions include maintaining cell shape, stabilizing attachment, facilitating transport and motility.
• Major Components:
  • Microtubules: Hollow structures made of tubulin, involved in maintaining cell shape and transporting materials.
  • Microfilaments: Composed of actin, contribute to cellular movement.
  • Intermediate Filaments: Provide tensile strength and structural support.

Microtubules

• Composed of 25 nm tubulin dimers, with protofilaments that stabilize their structure.
• Associated proteins (MAPs) assist in stabilization and binding to organelles, and motor proteins like kinesin or dynein aid in vesicle movement.

Test your understanding of cell membrane components, including glycoproteins, glycolipids, and types of membrane proteins. This quiz covers essential functions and structures involved in cellular communication and transport. Perfect for students studying cell biology.