Cell Structure and Cytology

Introduction to Cell Structure

  • Cytology: The study of cells, initiated with the invention of the compound/light microscope.
  • Microscopes:
    • Compound Light Microscope: Utilizes ocular and objective lenses to visualize specimens.
    • Electron Microscope: Offers higher resolution, revealing intricate details of cell structure using electron beams.

Measurement Units in Cytology

  • Micrometers and Nanometers:
    • 1 millimeter (mm) = 1000 micrometers (μm)
    • 1 micrometer (μm) = 1000 nanometers (nm)
    • Cell measurements often utilize micrometers, while nanometers are used for smaller cellular structures.

Cell Size Limitations

  • Cells maintain functions by regulating waste and nutrient exchange through their membranes.
  • As cell size increases, its volume grows faster than its surface area, leading to a potential inability to sustain life due to inadequate membrane function.

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic Cells:

    • Sizes: Typically 0.1 - 10 μm
    • Defined characteristics:
    • No nucleus (DNA is in nucleoid region)
    • No membrane-bound organelles
    • Smaller ribosomes
    • Example organisms: Bacteria

  • Eukaryotic Cells:

    • Sizes: Typically 10 - 100 μm
    • Defined characteristics:
    • True membrane-bound nucleus
    • Various membrane-bound organelles
    • Larger ribosomes
    • Example organisms: Protists, Fungi, Plants, and Animals

Plant Cell vs. Animal Cell

  • Plant Cell Features:
    1. Cell Wall
    2. Large Central Vacuole
    3. Chloroplasts
  • Animal Cell Features:
    • Contains organelles such as lysosomes, centrioles, and varies in the presence of structural components like the cell wall and chloroplasts.

Structure of Animal Cells

  • Components of Animal Cells:
    • Nuclear Envelope, Nucleus, Ribosomes, Rough and Smooth Endoplasmic Reticulum (ER), Golgi apparatus, Mitochondria, Lysosomes, etc.
    • The plasma membrane, mainly a phospholipid bilayer, acts as a gatekeeper for cell entry and exit.

The Nucleus

  • Function:
    • Acts as the control center for cell activities.
    • Stores DNA in chromatin form that encodes proteins crucial for cell function.
  • Structure:
    • Surrounded by a double membrane (Nuclear Envelope), featuring nuclear pores for molecular transport.

Endoplasmic Reticulum (ER)

  • Rough Endoplasmic Reticulum (RER):
    • Studded with ribosomes, facilitates the synthesis of proteins that enter the ER for processing.
  • Smooth Endoplasmic Reticulum (SER):
    • Lacks ribosomes, responsible for:
    • Synthesis of lipids (e.g., sterol hormones)
    • Detoxification processes

Key Functions of ER

  • Rough ER:
    • Involved in protein production and transport. RNA from ribosomes is translated to form proteins that the ER then envelopes in vesicles for transport.
  • Smooth ER:
    • Associated with lipid synthesis and detoxification, transporting these compounds within the cell.