Cell Biology Lecture Notes

Key Points

• Cells are the smallest living units of organisms.
• All cells share three common components:
  • Cell Membrane: Separates the cell from its environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

1. Eukaryotic Cells

   • More advanced and complex.
   • Contain organelles, including:
     • Nucleus: Control center of the cell containing DNA.
     • Other specialized organelles.
   • Found in plants and animals.

2. Prokaryotic Cells

   • Simpler than eukaryotic cells.
   • Lack a nucleus and membrane-bound organelles.
   • Always unicellular (e.g., bacteria).

Organelles

• Definition: "Little organs" within a cell performing specific functions.

Nucleus

• Contains DNA and directs cell activities.
• Contains Chromatin and Nucleolus.
  • Chromatin: Tangled DNA form.
  • Nucleolus: Site of ribosome production.

Ribosomes

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

Endoplasmic Reticulum (ER)

• Types:
  • Rough ER: Has ribosomes attached.
  • Smooth ER: No ribosomes attached.
• Function: Membrane passageway for transporting materials (e.g., proteins).

Golgi Apparatus

• Receives proteins from the ER.
• Modifies and packages proteins into usable forms.
• Customization processes include folding proteins and adding lipids or carbohydrates.

Vacuoles

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

Lysosomes

• Role: Garbage collectors of the cell.
• Contain enzymes that break down damaged or worn-out cell parts.

Mitochondria

• Powerhouses of the cell, responsible for producing ATP through cellular respiration.
• More mitochondria in cells requiring greater energy.

Cytoskeleton

• Maintains cell shape.
• Composed of:
  • Microfilaments: Thread-like protein structures.
  • Microtubules: Thin hollow tubes.

Unique Organelles

• Chloroplasts: Present in plant cells for photosynthesis; contain chlorophyll (green pigment).
• Cell Wall: Found in plant cells for support and protection (absent in animal cells).

Specialized Structures

• Cilia: Hair-like projections in the respiratory tract that help trap particles.
• Flagella: Tail-like structures that aid in cell movement (found in some bacteria and sperm cells).

Summary

• Eukaryotic cells: Contain a nucleus and membrane-bound organelles (plants and animals).
• Prokaryotic cells: Unicellular, lack nucleus and organelles (e.g., bacteria).
• All cells share the three main components: cell membrane, cytoplasm, and DNA.
• Both plant and animal cells have mitochondria, but only plant cells have chloroplasts.