Eukaryotic Cell Structure and Function

Overview of Eukaryotic Cells

  • Eukaryotic cells are characterized by cellular structures not found in prokaryotic cells (bacteria).

Differences Between Eukaryotic and Prokaryotic Cells

  • Funguses do not have a glycoplasm.
  • Animals and protozoa possess flagella (optionally).
    • In females, flagella are not present in any cell; in males, only sperm has flagella.
  • Flagella function primarily for motility (movement).

Flagella in Eukaryotic Cells

  • Structure of eukaryotic flagella:
    • Not hollow; comprised of elongated protein filaments.
    • Compared to thin copper wires under insulation.
    • Eukaryotic flagella are fragile and cannot extend themselves.
    • Cell membrane extends toward the flagella for protection—inspired by structure where the membrane envelops the flagella.

Nine-Plus-Two Arrangement

  • The arrangement of microtubules within flagella is referred to as the “nine-plus-two” arrangement, (though not always explicitly required to memorize).
  • Structural differences with prokaryotic flagella, which lack membrane protection.

Examples of Protozoa with Flagella

  • Giardia: a protozoan causing diarrhea; it possesses multiple flagella for movement.
  • Eukaryotic flagella create a whip-like movement, typically slower than prokaryotic flagella.

Cilia

  • Cilia are similar in structure to flagella but shorter in length.
  • Found in organisms such as Paramecium, which utilize numerous cilia for movement.
  • Used to create a feeding current that moves food toward specialized mouths in ciliated organisms.

Human Ciliated Cells

  • Humans possess cilia in areas such as:
    • Ears (e.g., auditory cells)
    • Lungs (clearing mucus and debris).

Mechanism of Mucus Movement in Lungs

  • Ciliated epithelial cells function to beat mucus upward to trap inhaled debris, facilitating clearance in the trachea.

Eukaryotic Cell Walls

  • Animal and protozoan cells do not have cell walls.
  • Fungi have cell walls made up of chitin, a complex carbohydrate.
    • Provide structural support against osmotic pressure.
    • Compare with plant cells, which use cellulose as their structural material.

Eukaryotic Cell Membrane

  • Structure follows the fluid mosaic model, featuring:
    • Phospholipid bilayer with embedded proteins.
    • Cholesterol is a functional component, providing stability and influencing membrane fluidity.

Effects of High Cholesterol Levels

  • Excess cholesterol can stiffen blood vessel membranes, leading to potential health issues such as arterial plaque formation.

Membrane Transport Mechanisms

  • Eukaryotic cells employ mechanisms of selective permeability similar to prokaryotic cells:
    • Simple diffusion, facilitated diffusion, and active transport.
  • Eukaryotic cells can engage in vesicular transport using:
    • Endocytosis: membrane engulfs material, forming vesicles to take in substances.
    • Exocytosis: vesicles fuse with the membrane, releasing material outside of the cell.

Types of Endocytosis

  • Phagocytosis: engulfing large particles (e.g., white blood cells consuming bacteria).
  • Pinocytosis: uptake of liquid containing small solutes, capturing groups of molecules.
  • Receptor-mediated endocytosis: involves receptors binding specific molecules and internalizing them via vesicles.

Organelles within Eukaryotic Cells

  • Nucleus: Largest organelle, housing genetic material (linear DNA).
    • The nuclear envelope protects DNA; it features nuclear pores allowing material exchange.
  • Endoplasmic Reticulum (ER): Continuous with the nuclear envelope:
    • Rough ER: Studded with ribosomes, primarily involved in protein synthesis.
    • Smooth ER: Synthesizes lipids.

Golgi Apparatus

  • Serves as the processing, packaging, and shipping center for cellular products.
  • Modifies, sorts, and distributes proteins received from the ER.

Lysosomes

  • Membrane-bound vesicles containing digestive enzymes to degrade waste material and cellular debris.
    • Effective in breaking down complex molecules and cellular components.

Mitochondria

  • Known as the powerhouses of cells, responsible for ATP production via cellular respiration.
  • Characterized by:
    • Double membrane structure (outer and inner membranes), with the inner membrane having folds called cristae.
    • Contains its own circular DNA and 70S ribosomes similar to bacteria, suggesting endosymbiotic origins.

Endosymbiotic Theory

  • Proposes that mitochondria and chloroplasts originated from prokaryotic cells engulfed by ancestral eukaryotic cells, providing an advantage through ATP production.

Chloroplasts

  • Present only in plant cells and algae, responsible for photosynthesis.
  • Share similar prokaryotic characteristics with mitochondria, exhibiting double membranes and containing circular DNA.

Summary

  • Eukaryotic cells display significant complexity involving organelles with specialized functions, contrasting with prokaryotic simplicity.
  • Understanding cell structure, membrane dynamics, and the unique adaptations of organelles like mitochondria and chloroplasts is critical for comprehending cellular processes.