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Cell Structure and Function

Fundamental Parts of a Cell

  • Cell Membrane (Plasma Membrane)

    • Acts as a barrier to control what enters and exits the cell.

    • Serves as a regulatory mechanism for sequestering internal environments.

Internal Environment of a Cell

  • Protoplasm vs. Cytoplasm

    • Protoplasm: An older term for the fluid inside a cell.

    • Cytoplasm: A more precise term that also includes the cytoskeletal network and organelles.

    • Cytoskeletal Network: Composed of three types of proteins providing structure and support to organelles.

Concept of Size Relationships among Organelles

  • Organelles have varying sizes and can be compared based on their dimensions (not required to memorize exact sizes).

  • Importance lies in functional relationships, e.g.:

    • Nucleus > Endoplasmic Reticulum > Mitochondria

  • Understanding size aids in comprehending interactions among organelles.

Types of Cells

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotes

    • Lack a nucleus (derived from Greek meaning "before kernel").

    • Includes two major domains: Bacteria and Archaea.

    • Universally possess the capability to synthesize all 20 amino acids.

    • Often unicellular but may form colonies.

  • Eukaryotes

    • Possess a nucleus and larger, more complex structures.

    • Structural Differences from Prokaryotes include:

      • DNA organized into linear chromosomes, complexed with proteins (histones).

      • Membrane-bound organelles.

      • Larger in size (5-20 micrometers) compared to prokaryotes (typically 1-10 micrometers).

Organelles Found in Prokaryotes

  • Thin Appendages: Aid in adhesion to surfaces (e.g. fimbriae).

  • Plasma Membrane: Serves as a selective barrier.

  • Cell Wall: Provides shape and protection.

  • Nucleoid Region: Contains circular DNA, not enclosed by a membrane.

  • Ribosomes: Sites for protein synthesis.

  • Capsule: A jelly-like protective layer.

  • Flagella: Structures for motility.

Microscopy and Visualization

  • Types of Microscopy

    • Light Microscopy: Limited resolution (~200 nanometers) and used for observing living cells.

    • Electron Microscopy: Provides high-resolution images; includes Transmission Electron Microscopy (TEM) for internal structures and Scanning Electron Microscopy (SEM) for surfaces.

    • Resolution: Ability to distinguish two close points; vital for cellular analysis.

The Significance of Bacteria

  • Diversity and Adaptability

    • Prokaryotes can survive in extreme environments (e.g., extremophiles)

    • Important Bacterial Groups:

      • Cyanobacteria: Essential for producing oxygen through photosynthesis.

      • Disease-Causing Bacteria: Only a fraction of known bacteria are pathogenic.

Classification of Bacteria

  • Shapes: Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral).

  • Movement: Some have flagella for motility.

  • Gram Staining: Differentiates bacteria based on cell wall structure—Gram-positive stains purple; Gram-negative stains pink due to varying peptidoglycan content.

Key Functional Differences between Prokaryotes and Eukaryotes

  • Nucleus: Present in eukaryotes; absent in prokaryotes.

  • DNA Arrangement: Circular in prokaryotes vs. linear, complexed with proteins in eukaryotes.

  • Cell Wall Composition: Prokaryotic cell walls contain peptidoglycan; eukaryotic cells often have an extracellular matrix.

  • Cell Reproduction: Eukaryotic cells reproduce sexually; prokaryotic cells typically reproduce asexually through binary fission.