Lecture on Cytology

Introduction to Cytology

• Cytology: study of cells.
• Cells: smallest independent unit of life, fundamental unit.
• Bacteria are unicellular, viruses aren't alive. Humans are multicellular with 75 trillion cells.

Cell Structure

• Size and Composition:

  • Cells measured in microns (1 micron = 1000th of a millimeter).
  • Largest human cell: anterior horn cell in spinal cord (135 microns).
  • Human egg visible to naked eye (120 microns).
  • Red blood cell: 5-8 microns.

• Cell Shape and Function:

  • Shape dictates function (e.g., round cells, spindle muscle cells).
  • Stem cells differentiate into specialized cells.

Basic Cell Components

• Cytosol: Watery, salty fluid inside the cell.
• Cell Membrane:
  • Phospholipid bilayer, semi-permeable.
  • Contains proteins for channels, pores, and receptors.
  • Glycocalyx: sugary film important for communication.

Organelles

• Nucleus: Contains genetic material (DNA).
• Endoplasmic Reticulum (ER):
  • Rough ER: synthesizes proteins.
  • Smooth ER: synthesizes lipids.
• Golgi Apparatus: Packages and exports materials.
• Lysosomes: Contains enzymes to break down materials.
• Centrioles: Important for cell division.
• Mitochondria: Produces ATP, energy powerhouse.

Genetic Material

• Chromosomes: DNA organized into genes.
• Gene: Code for one protein.
• DNA vs RNA:
  • DNA: double helix, stays in nucleus.
  • RNA: single strand, messenger RNA (mRNA) carries genetic info out of nucleus.

Protein Synthesis

• Transcription: Copying DNA to mRNA in nucleus.
• Translation: mRNA read by ribosomes to assemble proteins from amino acids.
• RNA Types:
  • Messenger RNA (mRNA): carries code.
  • Ribosomal RNA (rRNA): part of ribosome.
  • Transfer RNA (tRNA): matches amino acids to mRNA codons.

Cell Division

• Mitosis: Division for growth and renewal; involves phases (prophase, metaphase, anaphase, telophase).
• Meiosis: Reduction division for gamete formation.

Transport Mechanisms

• Passive Transport: No energy required.

  • Diffusion, facilitated diffusion, osmosis, filtration.

• Active Transport: Requires energy (ATP).

  • Pumps (e.g., sodium-potassium pump).

• Endocytosis and Exocytosis:

  • Endocytosis: Intake of substances (e.g., phagocytosis, pinocytosis).
  • Exocytosis: Release of substances from the cell.

Conclusion

• Cytology covers the fundamental structure and function of cells, includes understanding cell division and transport mechanisms.
• Key Concepts: Importance of cell membrane, genetic material, and energy production.