Lecture Notes: Introduction to Cells

Overview of Cells

• Definition: Smallest living units of an organism.
• Common Features: All cells have:
  • Cell Membrane: Separates the inside of the cell from its environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

1. Eukaryotic Cells:
   • Have organelles including a nucleus.
   • Found in plants and animals.
   • More advanced and complex.
2. Prokaryotic Cells:
   • No nucleus or membrane-enclosed organelles.
   • Genetic material not contained within a nucleus.
   • Always unicellular organisms (e.g., bacteria).

Organelles and Their Functions

• Nucleus:
  • Control center of the cell.
  • Contains DNA which dictates cell functions.
  • Chromatin: Tangled form of DNA inside the nuclear membrane.
  • Chromosomes: Condensed DNA structures for cell division.
  • Nucleolus: Structure where ribosomes are made.
• Ribosomes:
  • Synthesize proteins.
  • Found floating in cytoplasm or attached to the endoplasmic reticulum (ER).
• Endoplasmic Reticulum (ER):
  • Rough ER: Has ribosomes attached, involved in protein synthesis.
  • Smooth ER: No ribosomes, involved in transport of materials.
• Golgi Apparatus (Golgi Body):
  • Customizes proteins by folding them or adding other materials (lipids, carbohydrates).
• Vacuoles:
  • Store various materials.
  • Central Vacuole (plant cells): Stores water.
• Lysosomes:
  • Garbage collectors, breakdown cellular debris with enzymes.
• Mitochondria:
  • Powerhouse of the cell.
  • Site of cellular respiration, produces ATP.
  • Cells needing more energy have more mitochondria.
• Cytoskeleton:
  • Maintains cell shape.
  • Includes microfilaments (protein threads) and microtubules (hollow tubes).
• Chloroplasts (plant cells):
  • Site of photosynthesis.
  • Contains green pigment chlorophyll.
• Cell Wall (plant cells):
  • Provides shape, support, and protection.
  • Not present in animal cells.

Unique Cell Structures

• Cilia (e.g., in respiratory tract cells):
  • Microscopic hair-like projections.
  • Move in waves to trap and expel particles.
• Flagella (e.g., in some bacteria and human sperm cells):
  • Tail-like structure that aids in movement.

Summary

• Eukaryotic Cells: Plant and animal cells with a nucleus and organelles.
• Prokaryotic Cells: Unicellular organisms without a nucleus and organelles.
• All cells have a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria, but only plant cells have chloroplasts.