Prokaryotic and eukaryotic cells, cell membrane, cell wall, nucleus, organelles

1. Introduction to Cells

• The cell is the basic structural and functional unit of life.
• Cells can be classified into prokaryotic and eukaryotic cells.
• The study of cells is called cytology.
• The concept of the cell theory was proposed by Schleiden and Schwann.
• Rudolf Virchow added that "all cells arise from pre-existing cells."

2. Prokaryotic and Eukaryotic Cells

• Prokaryotic Cells:
  • Do not have a membrane-bound nucleus.
  • Genetic material is present in a region called the nucleoid.
  • Examples: Bacteria and Archaea.
• Eukaryotic Cells:
  • Have a well-defined nucleus surrounded by a nuclear membrane.
  • Contain membrane-bound organelles.
  • Examples: Plants, Animals, Fungi, Protists.

3. Cell Membrane (Plasma Membrane)

• Present in both prokaryotic and eukaryotic cells.
• Composed of a phospholipid bilayer with embedded proteins.
• Regulates the movement of substances in and out of the cell (selectively permeable).
• Described by the Fluid Mosaic Model proposed by Singer and Nicolson.

4. Cell Wall

• Found in plant cells, bacteria, fungi, and some protists.
• Provides structural support and protection.
• Composed of cellulose in plants, chitin in fungi, and peptidoglycan in bacteria.

5. Nucleus

• Present in eukaryotic cells.
• Contains genetic material (DNA) that controls cell functions.
• Surrounded by a nuclear membrane.
• Contains a nucleolus where ribosomes are synthesized.

6. Cell Organelles

• Endoplasmic Reticulum (ER):
  • Rough ER has ribosomes and is involved in protein synthesis.
  • Smooth ER lacks ribosomes and synthesizes lipids and steroids.
• Ribosomes: Site of protein synthesis; found in both prokaryotic and eukaryotic cells.
• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
• Mitochondria: Powerhouse of the cell, responsible for ATP production.
• Lysosomes: Contain digestive enzymes to break down waste and foreign substances.
• Peroxisomes: Detoxify harmful substances like hydrogen peroxide.
• Centrioles: Help in cell division (found in animal cells).
• Chloroplasts: Present in plant cells, responsible for photosynthesis.
• Vacuoles: Store nutrients and waste products; large in plant cells.

7. Differences Between Prokaryotic and Eukaryotic Cells

8. Conclusion

• Cells are the fundamental units of life.
• Prokaryotic cells lack a true nucleus and organelles.
• Eukaryotic cells have a defined nucleus and various organelles.
• Cell structures work together to maintain life functions.