Bio3

Cell Biology: Structure and Types

Introduction to Cells and Cell Theory

  • Cells are the fundamental structural unit of all living organisms.
  • Key principles, known as the Cell Theory, summarize observations about cells:
    1. All living organisms are composed of cells.
    2. The cell is the basic unit of life.
    3. All cells arise from pre-existing cells.

Historical Basis and Pillars of Cell Theory

  • The development of Cell Theory is based on observations of
    • Cork, embryos, elder pith, toad cartilage that led to the conclusion that all organisms are cell-based.
  • Modern Cell Theory emphasizes three main pillars:
    1. Composition of all living things includes cells.
    2. Cells as the basic unit of life.
    3. The continuity of cell life via cell division.

Relative Sizes of Particles and Cells

  • Size range of biological entities varies, necessitating microscope use:
    • Comparison Chart of Sizes:
    • Atoms: Carbon atom (340 pm)
    • Molecules: Adenine, Glucose
    • Cellular Components: Ribosomes
    • Viruses: Various Virus Sizes
    • Bacteria: Various Bacterial Sizes
    • Eukaryotic Cells: Red blood cells, skin cells
    • Large Protists: Amoeba proteus (500 μm)
Constraint on Cell Size
  • The surface area to volume ratio (SA:V) is a key constraint on cell size, influencing cellular efficiency and functionality.

Cell Classification and Universal Structures

  • All cells can be categorized into two major types:
    1. Prokaryotes: Includes Bacteria and Archaea
    • Examples: Staphylococcus sp., Bacillus sp.
    1. Eukaryotes: Includes kingdoms such as Protists, Fungi, Plants, and Animals.
Structures Common to All Cells
  • Common structural components in all cells include:
    • Cell Membrane: Composed of lipids, defining cell boundaries.
    • Cytoplasm: Aqueous solution where biological reactions occur.
    • Genetic Material: All cells possess genetic material (DNA).

Prokaryotic Cell Structure and Function

  • Prokaryotes are the simpler, smaller forms of life, typically ranging from 0.50.5 to 6 extμm6 \, ext{μm}.
  • Key features of prokaryotic cell structure are:
    1. Lack of Nucleus: Genetic material in a nucleoid region, NOT membrane-bound.
    2. Cell Wall: Composed of peptidoglycan, providing structural integrity.
    3. Ribosomes: Smaller than e