Cell Biology Lecture Notes

Introduction to Cells

• Cells are the smallest living units of organisms.
• Common features of all cells:
  • Cell Membrane: Separates the inside of the cell from its environment.
  • Cytoplasm: Jelly-like fluid within the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

1. Eukaryotic Cells

   • More advanced and complex.
   • Contain organelles (e.g., nucleus, mitochondria).
   • Found in plants and animals.

2. Prokaryotic Cells

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

Organelles

• Definition: "Little organ"; specialized parts of a cell with unique jobs.

Key Organelles

• Nucleus:

  • Control center of the cell containing DNA.
  • Chromatin: Tangled form of DNA within the nuclear membrane.
  • Chromosomes: Condensed DNA structures during cell division.
  • Nucleolus: Site for ribosome production.

• Ribosomes:

  • Synthesizers of proteins.
  • Can be free-floating in the cytoplasm or attached to the endoplasmic reticulum (ER).

• Endoplasmic Reticulum (ER):

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

• Golgi Apparatus (Golgi Body):

  • Receives materials from the ER, customizes them, and packages them for use.

• Vacuoles:

  • Sac-like structures that store materials (e.g., water in plant cells).

• Lysosomes:

  • Garbage collectors that break down damaged or worn-out cell parts using enzymes.

• Mitochondria:

  • Powerhouse of the cell, produces ATP through cellular respiration.
  • More abundant in energy-demanding cells.

• Cytoskeleton:

  • Maintains cell shape; includes microfilaments and microtubules.

• Chloroplasts (in plants):

  • Site of photosynthesis; contains chlorophyll (green pigment).

• Cell Wall (in plants):

  • Provides shape, support, and protection; absent in animal cells.

Unique Features in Cells

• Cilia: Microscopic hair-like projections in the respiratory tract that help trap and expel particles.
• Flagella: Tail-like structure for movement; present in some bacteria and sperm cells.

Summary

• Eukaryotic Cells: Have a nucleus and organelles; found in plants and animals.
• Prokaryotic Cells: Unicellular; lack a nucleus and membrane-enclosed organelles.
• All cells possess a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria; only plant cells have chloroplasts.