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.