Cytology Lecture Notes

Introduction to Cytology

• Cytology is the study of cells.
• Cells are the basic unit of life.
  • Bacteria are unicellular living organisms.
  • Viruses are not considered living.
• Humans are multicellular, with an adult human having approximately 75 trillion cells.

Size and Structure of Cells

• Cells are measured in microns (1,000 microns in a millimeter).
• Largest cells: Anterior horn cells in the spinal cord (135 microns).
• Human egg: 120 microns, visible to the naked eye.
• Red blood cells: 5-8 microns.
• Cell shape dictates function (e.g., muscle cells are spindle-shaped for contraction).

Cell Differentiation and Function

• Stem cells differentiate into specialized cells like red blood cells and nerve cells.
• Basic cell structure includes a fluid (cytosol) and a nucleus.
• Organelles perform specific functions within the cell.

Cell Structures and Organelles

• Cell Membrane: Semi-permeable phospholipid bilayer.
  • Contains proteins like channels and receptors for substance transport and communication.
• Nucleus: Contains genetic material, surrounded by a double membrane.
  • Contains nucleolus for ribosome production.
• Cytoskeleton: Supports cell shape and provides pathways for intracellular transport.
• Mitochondria: Powerhouse of the cell, produces ATP.
• Endoplasmic Reticulum (ER):
  • Rough ER: Studded with ribosomes, synthesizes proteins.
  • Smooth ER: Synthesizes lipids.
• Golgi Apparatus: Packages and distributes proteins and lipids.
• Lysosomes: Contain enzymes for digestion and waste removal.
• Centrioles: Involved in cell division, organizing chromosomes.

DNA, RNA, and Protein Synthesis

• DNA is a double helix containing genetic instructions.
• Genes code for proteins, with DNA being transcribed to mRNA in the nucleus.
• mRNA is translated into proteins at ribosomes.
• Types of RNA:
  • mRNA (Messenger RNA): Carries genetic information.
  • rRNA (Ribosomal RNA): Part of ribosome structure.
  • tRNA (Transfer RNA): Brings amino acids to ribosomes during protein synthesis.
• Transcription: Copying DNA to RNA.
• Translation: Converting RNA sequence into amino acid sequence (protein).

Cell Division: Mitosis and Meiosis

• Mitosis: Produces two identical daughter cells, essential for growth and cell renewal.
  • Phases: Prophase, Metaphase, Anaphase, Telophase.
• Meiosis: Produces gametes (sperm and eggs), reducing chromosome number by half.

Transport Mechanisms

• Passive Transport: Movement without energy.
  • Simple diffusion, facilitated diffusion, osmosis (water movement through semi-permeable membrane).
• Active Transport: Requires energy (ATP) to move substances against concentration gradients.
  • Example: Sodium-potassium pump.
• Endocytosis: Bringing substances into the cell.
  • Phagocytosis (eating), Pinocytosis (drinking).
• Exocytosis: Expelling substances from the cell.

Conclusion

• The lecture covered the basic structure and function of cells, including their components and processes like protein synthesis, cell division, and transport mechanisms.
• Emphasized the importance of understanding cell structure and function in biology and physiology.