Cell Biology Lecture Notes

Introduction to Cells

• Definition: Cells are the smallest living units of an organism.
• Common Characteristics: All cells have three things in common:
  • Cell Membrane: Separates the inside of the cell from its environment.
  • Cytoplasm: A jelly-like fluid within the cell.
  • DNA: The genetic material of the cell.

Types of Cells

1. Eukaryotic Cells

   • Characteristics:
     • Have organelles, including the nucleus.
     • More advanced and complex, found in plants and animals.

2. Prokaryotic Cells

   • Characteristics:
     • Lack a nucleus and membrane-enclosed organelles.
     • Genetic material is not contained within a nucleus.
     • Always unicellular (e.g., bacteria).

Organelles

• Definition: Organelles are specialized parts of a cell that perform unique functions.

Key Organelles

• Nucleus:

  • Control center of the cell.
  • Contains DNA and dictates cell functions.
  • Contains chromatin (spread out form of DNA) and condenses into chromosomes during cell division.
  • Contains a nucleolus where ribosomes are made.

• Ribosomes:

  • Synthesizes (makes) proteins.
  • Can be free in the cytoplasm or attached to the Endoplasmic Reticulum (ER).

• Endoplasmic Reticulum (ER):

  • A membrane-enclosed passageway for transporting materials.
  • Types:
    • Rough ER: Has ribosomes attached.
    • Smooth ER: Lacks ribosomes.

• Golgi Apparatus (Golgi Body):

  • Receives proteins from the ER for modification (folding and adding materials).

• Vacuoles:

  • Sac-like structures that store materials.
  • Central Vacuole in plant cells stores water.

• Lysosomes:

  • Acts as garbage collectors, breaking down damaged or worn-out cell parts.
  • Contains enzymes for cellular debris breakdown.

• Mitochondria:

  • Powerhouse of the cell responsible for cellular respiration.
  • Produces ATP molecules for energy.
  • Cells requiring more energy have more mitochondria.

• Cytoskeleton:

  • Maintains cell shape.
  • Composed of microfilaments (protein threads) and microtubules (thin hollow tubes).

• Chloroplasts:

  • Found in plant cells, site of photosynthesis.
  • Contains chlorophyll, giving plants their green color.

• Cell Wall:

  • Only in plant cells, provides shape, support, and protection.
  • Animal cells do not have a cell wall.

Unique Structures in Cells

• Cilia:

  • Microscopic hair-like projections in human respiratory tract cells.
  • Help trap and expel particles.

• Flagella:

  • Tail-like structures in some bacteria for movement.
  • Only human cell with flagellum is the sperm cell.

Summary

• Eukaryotic Cells: Have a nucleus and membrane-enclosed organelles (plants and animals).
• Prokaryotic Cells: Unicellular, lack nucleus and membrane-enclosed organelles.
• Common Features: All cells have a cell membrane, cytoplasm, and genetic material.
• Energy Organelles: Both plant and animal cells contain mitochondria, while only plant cells have chloroplasts.