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).