Eukaryotes

Evolution of Eukaryotic Life

  • Dramatic Evolutionary Change

    • Transition from prokaryotic to eukaryotic life is significant due to complexity.

  • Major Differences

    • Prokaryotes:
    • Small, simple cells without organelles.
    • Examples: bacteria.
    • Eukaryotes:
    • Large, complex cells with organelles.
    • Include protists, fungi, plants, and animals.

Mechanisms of Eukaryotic Evolution

  • Cell Specialization:

    • Increased size and cell compartments lead to specialized functions.
    • Eukaryotic cells exhibit regional specialization (e.g., different ribosomes for different functions).

  • Theories of Eukaryote Evolution:

    • Autogenesis Theory: Cells internalize parts of themselves to form compartments.
    • Advantage: Specialization and increased surface area for membranes.
    • Endosymbiotic Theory: Prey or parasite become internalized, forming a mutualistic relationship, resulting in organelles (e.g., mitochondria).
    • Advantage: Increased functionality and specialization of organelles.
    • Symbiogenesis: New species or organelles arise from symbiotic relationships.
    • Advantage: Enhancing potential for specialization.

Evidence Supporting Theories

  • Observations Indicating Evolutionary History:
    • Cell size and structure similarity.
    • Homology of prokaryotic membranes.
    • Mechanisms like binary fission observed in both.
    • Genetic structure: supercoiled, circular DNA loops in mitochondria.

Diploidy and Sexual Reproduction

  • Significance of Evolution of Diploidy:

    • Diploidy allows for genetic variation through sexual reproduction (mitosis and meiosis).

  • Mitosis vs. Meiosis:

    • Mitosis: Cell division resulting in two identical diploid cells (growth and repair).
    • Meiosis: Process producing four haploid gametes, allowing genetic diversity in offspring.

Organelles in Eukaryotic Cells

  • Plasma Membrane:

    • Phospholipid bilayer with proteins; regulates entry and exit of substances, involved in communication.

  • Nucleus:

    • Contains DNA, site of transcription; controls cell activities.

  • Endoplasmic Reticulum (ER):

    • Rough ER: Studded with ribosomes, modifies proteins.
    • Smooth ER: Synthesizes lipids, detoxifies drugs.

  • Ribosomes:

    • Free ribosomes produce proteins for use within the cytoplasm.
    • Bound ribosomes produce proteins for export or membrane insertion.

  • Golgi Apparatus:

    • Modifies, sorts, and ships proteins and lipids; packages them into vesicles for transport.

  • Lysosomes:

    • Contain digestive enzymes; break down waste and cellular debris.

  • Mitochondria:

    • Powerhouse of the cell; produces ATP via cellular respiration, contains its own DNA.

  • Cytoskeleton:

    • Composed of microtubules, microfilaments, and intermediate filaments; provides structural support and facilitates movement within the cell.

Variations in Cellular Structures and Function

  • Dynamic Nature of Cells:

    • Cells undergo constant changes and adapt to internal and external signals. This adaptability is crucial for survival.

  • Genetic Diseases:

    • All genetic diseases can be traced to cellular-level changes, often involving mutations that affect protein functionality.

  • Cell Differentiation:

    • Variation in macromolecules (proteins, lipids, carbohydrates) and cellular structures leads to specialized functions.
    • Different genes are expressed in different cell types, creating diversity in cellular function despite identical genetic information.