Lecture Notes: Cell and Subcellular Organelles

Introduction

• Lecturer: Dr. Suresh
• Topic: Cells and Subcellular Organelles
• Relevance: Understanding cellular structure is fundamental in biochemistry to comprehend the chemical reactions in living systems.

Basics of Cells

• Definition: Cells are considered the basic unit of life.
• Types:
  • Prokaryotic Cells: Simple structure, lack a well-defined nucleus, possess a cell wall.
  • Eukaryotic Cells: Complex structure, have a well-defined nucleus, enclosed by a cell membrane.

Structural Components of Eukaryotic Cells

• Cell Membrane: Rigid structure enclosing the cell.
• Subcellular Organelles:
  • Plasma Membrane
  • Microtubules and Centrioles
  • Nucleolus and Nucleus
  • Golgi Complex
  • Smooth and Rough Endoplasmic Reticulum
  • Lysosomes and Cytoplasm
  • Mitochondria
  • Ribosomes
  • Chromatin, Nuclear Pore, Nuclear Envelope

Differences Between Prokaryotic and Eukaryotic Cells

• Size:
  • Prokaryotic: 1-10 micrometers
  • Eukaryotic: 10-100 micrometers
• Cell Membrane and Wall:
  • Prokaryotic: Cell wall, no cell membrane
  • Eukaryotic: Cell membrane
• Cytoplasm:
  • Prokaryotic: Viscous, lacks organelles
  • Eukaryotic: Contains various organelles
• Nucleus:
  • Prokaryotic: Not well-defined, no nuclear membrane
  • Eukaryotic: Well-defined, contains nucleolus
• Mitochondria:
  • Absent in prokaryotes
  • Present in eukaryotes
• Golgi Complex and Cytoskeleton:
  • Absent in prokaryotes
  • Present in eukaryotes
• Cell Division:
  • Prokaryotes: Binary fission
  • Eukaryotes: Mitosis

Isolation of Subcellular Organelles

• Technique: Ultracentrifugation
  • Based on molecular weight, heavier organelles sediment first.
  • Different subcellular organelles can be isolated at varying centrifugal rates.
• Examples of Isolation:
  • 800 rotations/min for 10 mins: Cell membrane fragments
  • 13,000 rotations/min for 10 mins: Nucleus
  • 100,000 rotations/min for 60 mins: Mitochondria, lysosomes, peroxisomes
  • 200,000 rotations/min for 3 hours: Endoplasmic reticulum fragments
  • Ribosomes can be isolated after cytosol separation.
• Markers for Isolation:
  • Nucleus: DNA
  • Lysosomes: Cathepsin
  • Mitochondria: Krebs cycle enzymes (e.g., alpha-ketoglutarate dehydrogenase)
  • Cytoplasm: Lactate dehydrogenase

Conclusion

• Ultracentrifugation is essential for isolating and studying subcellular organelles in eukaryotic cells.
• Understanding the structure and function of cells is crucial for studying biochemical processes.