Cell Biology Lecture Notes

Key Concepts

• Cells are the smallest living units of organisms.
• All cells share three common features:
  • Cell membrane: Separates the cell from its environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: The cell's genetic material.

Categories of Cells

1. Eukaryotic Cells

   • Have organelles (e.g., nucleus).
   • More complex, found in plants and animals.

2. Prokaryotic Cells

   • Lack a nucleus and membrane-enclosed organelles.
   • Always unicellular (e.g., bacteria).

Organelles Overview

• Definition: Specialized parts of a cell with unique functions.

Nucleus

• Control center of the cell.
• Contains DNA (genetic material).
• Chromatin: Tangled form of DNA found inside the nuclear membrane.
• DNA condenses into chromosomes when the cell divides.
• Contains nucleolus: Structure where ribosomes are made.

Ribosomes

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

Endoplasmic Reticulum (ER)

• Membrane-enclosed passageway for transporting materials.
• Two types:
  • Rough ER: Has ribosomes attached.
  • Smooth ER: No ribosomes.

Golgi Apparatus (Golgi Body)

• Receives proteins from the ER.
• Customizes proteins into usable forms by folding or adding materials (lipids, carbohydrates).

Vacuoles

• Sac-like structures that store different materials.
• Central vacuole in plant cells: Stores water.

Lysosomes

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

Mitochondria

• Powerhouse of the cell.
• Produces ATP through cellular respiration, providing energy for cell activities.
• More mitochondria in energy-demanding cells.

Cytoskeleton

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

Chloroplasts (in Plant Cells)

• Site of photosynthesis.
• Contains chlorophyll, making it green.

Cell Wall (in Plant Cells)

• Provides shape, support, and protection.
• Animal cells do not have a cell wall.

Unique Cell Features

• Cilia: Hair-like projections in some human cells (e.g., respiratory tract) that help trap particles.
• Flagella: Tail-like structure for movement found in some bacteria and sperm cells.

Summary

• Eukaryotic cells: Plant and animal cells with a nucleus and membrane-bound organelles.
• Prokaryotic cells: Unicellular organisms without these features.
• All cells possess a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria; only plant cells have chloroplasts.