Cell Structure and Organisation Notes

ORGANISATION AND MAINTENANCE OF ORGANISM
CELL STRUCTURE AND ORGANISATION
  • Cell Definition: The basic structural, functional, and biological unit of all known living organisms; derived from the Latin word "cella" meaning "small room".
  • Structure: Tiny, box-like structures.
DISCOVERY OF CELLS
  • Robert Hooke (1665): First to discover cells.
  • Theodor Schwann & Matthias Schleiden (1839): Formulated the theory that all living things are made of cells.
  • Rudolf Virchow: Proposed that all cells come from pre-existing cells.
CHARACTERISTICS OF ALL CELLS
  • Surrounding Membrane: Protects and regulates the cell’s internal environment.
  • Cytoplasm: The thick liquid containing cell contents.
  • Organelles: Structures within the cell that perform specific functions.
  • Control Center: Most cells contain a nucleus with DNA.
CELL TYPES
  • Prokaryotic Cells: Lack a membrane-bound nucleus and organelles.
  • Eukaryotic Cells: Have a nucleus and organelles enclosed in membranes.
PROKARYOTIC CELLS
  • Characteristics:
    • No membrane-bound nucleus; genetic material is in a nucleoid region.
    • Organelles are not membrane-bound (e.g., ribosomes).
    • Examples: Bacteria and Archaea.
    • Small size (about 5 micrometers).
    • Circular "naked" DNA in the cytoplasm.
    • Rigid cell wall composed of glycoproteins (Murein).
    • Cell division occurs via binary fission.
    • Few organelles, all non-membrane bound.
EUKARYOTIC CELLS
  • Characteristics:
    • Have a membrane-bound nucleus containing linear chromosomes.
    • Include fungi, protists, plants, and animal cells.
    • Larger size (up to 40 micrometers).
    • Possess many organelles (some with double membranes):
    • Golgi apparatus, mitochondria, lysosomes.
    • Rigid cell walls: Fungi (chitin), plants (cellulose), and animals (generally no cell wall).
    • Cell division through mitosis and sexual reproduction via meiosis.
CELL MEMBRANE
  • Definition: Thin layer of cytoplasm that surrounds the cell and separates intracellular components from the extracellular environment.
  • Functions:
    • Maintains cell structure and chemical reactions in the cytoplasm.
    • Selectively permeable to regulate substance entry and exit (e.g., nutrients in, waste out).
    • Anchors the cytoskeleton for cell shape and aids in tissue formation by attaching to other cells.
THE FLUID-MOSAIC MODEL OF MEMBRANE
  • Proposed in 1972 by Jonathan Singer and Garth Nicolson: Describes the structure of biological membranes as a fluid structure with proteins embedded in lipid bilayers.
  • Components:
    • Lipid Bilayer: Consists of phospholipids forming a barrier between aqueous environments.
    • Proteins: Facilitate specific functions, such as selective transport and cell-cell recognition.
    • Cholesterol: Stabilizes the membrane at varying temperatures.
MEMBRANE COMPONENTS
  • Integral Membrane Proteins: Embedded within the phospholipid bilayer.
  • Peripheral Membrane Proteins: Located on the membrane surface.
  • Glycolipids: Carbohydrates attached to lipids; assist in cell recognition.
  • Glycoproteins: Carbohydrates attached to proteins; aid in adhesion and signaling.
CYTOPLASM
  • Composition: Approximately 90% water, containing dissolved salts and sugars, larger molecules (fats and proteins), and organelles.
  • Function: Site for numerous chemical reactions; essential for energy production and cellular maintenance.