Lecture Notes on Cell Biology

Introduction to Cells

• Cells are the smallest living units of an organism.
• Common features of all cells:
  • 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 (advanced, complex cells).
   • Organelles perform specialized functions.

2. Prokaryotic Cells

   • Do not have a nucleus or membrane-enclosed organelles.
   • Genetic material not contained within a nucleus.
   • Unicellular organisms, e.g., bacteria.

Organelles and Their Functions

• Nucleus

  • Control center of the cell.
  • Contains DNA (dictates cell function).
  • Chromatin: Form of DNA inside the nuclear membrane.
  • Chromosomes: Condensed DNA during cell division.
  • Nucleolus: Site of ribosome production.

• Ribosomes

  • Synthesize proteins.
  • Float in cytoplasm or attach to the endoplasmic reticulum (ER).

• Endoplasmic Reticulum (ER)

  • Rough ER: Has ribosomes; involved in protein synthesis.
  • Smooth ER: Lacks ribosomes.
  • Transports materials within the cell.

• Golgi Apparatus

  • Customizes proteins by folding and adding lipids or carbohydrates.

• Vacuoles

  • Store materials (e.g., central vacuole in plant cells stores water).

• Lysosomes

  • Garbage collectors; break down cellular debris using enzymes.

• Mitochondria

  • Powerhouse of the cell; performs cellular respiration.
  • More abundant in cells requiring more energy.

• Cytoskeleton

  • Maintains cell shape.
  • Made of microfilaments and microtubules.

• Chloroplasts (unique to plant cells)

  • Site of photosynthesis.
  • Contains chlorophyll (green pigment).

• Cell Wall (only in plant cells)

  • Provides shape, support, and protection.

Additional Cell Structures

• Cilia

  • Found in human respiratory tract; help expel inhaled particles.

• Flagella

  • Present in some bacteria and human sperm cells; aid in movement.

Summary

• Eukaryotic Cells: Plant and animal cells with nucleus and organelles.
• Prokaryotic Cells: Unicellular organisms without organelles or nucleus.
• All cells share cell membrane, cytoplasm, and DNA.
• Only plant cells have chloroplasts, but both plant and animal cells have mitochondria.