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2.2 Eukaryotic Cell Structure

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2.2 Eukaryotic Cell Structure

Overview of Eukaryotic Cell Structure

  • Eukaryotic cells are characterized by having a true nucleus.

  • The nuclear material is enclosed by a membranous nuclear envelope.

  • Eukaryotic cells contain various membrane-bound organelles.

  • Organisms like animals and plants are classified as eukaryotic.

Differences Between Animal and Plant Cells

  • Shape:

    • Plant cells usually have a more rectangular or squared-off shape due to the presence of a cell wall.

    • Animal cells do not have a cell wall and thus can be more irregularly shaped.

  • Both cell types have a cell membrane but differ in the presence of a cell wall in plants.

Key Organelles in Eukaryotic Cells

  • Nucleus:

    • The most noticeable organelle in eukaryotic cells, typically visible under a microscope.

    • Contains the majority of the cell's DNA.

    • Enclosed by a double membrane called the nuclear envelope, which has pores for transport.

  • Ribosomes:

    • Composed of ribosomal RNA and proteins; involved in protein synthesis.

    • Can be free in cytosol or bound to the endoplasmic reticulum (ER) or nuclear envelope.

    • Not membrane-bound, so they are not classified as true organelles.

Endoplasmic Reticulum (ER)

  • Structure:

    • A network of membranous tubules and sacs called cisternae.

  • Types of ER:

    • Rough ER:

      • Studded with ribosomes; synthesizes secretory proteins (e.g., hormones, enzymes) and membrane proteins.

    • Smooth ER:

      • Lacks ribosomes; responsible for lipid synthesis, carbohydrate metabolism, detoxification, and calcium storage.

Golgi Apparatus

  • Functions as a transport warehouse for products from the rough ER.

  • Modifies proteins and synthesizes carbohydrates before releasing them inside or outside the cell via vesicles.

Lysosomes

  • Known as the digestive compartments of the cell, containing hydrolytic enzymes.

  • Responsible for digesting macromolecules into smaller parts for cellular use.

  • Involved in:

    • Phagocytosis: Engulfing external particles.

    • Autophagy: Recycling damaged cellular components.

Vacuoles

  • Membrane-lined spaces in the cell filled with fluid, serving various functions:

    • Food Vacuoles: Formed by phagocytosis.

    • Contractile Vacuoles: Expel excess water to maintain ion concentration.

    • Central Vacuole (in plants): Contains cell sap, playing a role in growth and storage.

Mitochondria

  • Often referred to as the powerhouse of the cell; site of cellular respiration.

  • Number per cell varies widely (1 to thousands) depending on the type of cell.

  • Mobile organelles that provide energy for cellular functions.

Chloroplasts (in Plants)

  • Convert light energy into chemical energy through photosynthesis.

  • Found in leaves and green parts of plants; smaller than mitochondria.

Cytoskeleton

  • A network of fibers that extends throughout the cytoplasm, providing mechanical support and playing a role in cell movement.

Case Study: Cerebellar Ataxia in Dogs

  • Cerebellar Ataxia: A degenerative disease affecting the nervous system, characterized by:

    • Slurred speech, stumbling, poor coordination.

  • Involves progressive loss of cerebellar brain matter.

  • Mutation identified in gene SEL1L linked to protein packaging failure, leading to cell death.

  • Research may lead to targeted drugs to alleviate symptoms and slow progression.

Summary Questions

  • Match Organelles with Functions:

    • A: Mitochondria & Photosynthesis - Incorrect (they are involved in cellular respiration).

    • B: Central Vacuole & Storage - Correct (contains cell sap and aids in plant growth).

    • C: Ribosomes & Lipid Manufacture - Incorrect (this occurs in the smooth ER).

    • D: Nucleus & Cellular Respiration - Incorrect (occurs in mitochondria).

    • E: Lysosomes & Movement - Incorrect (involved in digestion).