Cell Biology Lecture Notes

Introduction to Cells

• Cells are the smallest living units of an organism.
• All cells have three common components:
  • 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.
   • More complex, 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 Overview

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

Nucleus

• Control center of the cell.
• Contains DNA that dictates cell functions.
• Chromatin: Tangled form of DNA found inside the nuclear membrane.
• During cell division, DNA condenses into chromosomes.
• Contains a nucleolus, where ribosomes are made.

Ribosomes

• Synthesize proteins.
• Can be free-floating in cytoplasm or attached to Endoplasmic Reticulum (ER).

Endoplasmic Reticulum (ER)

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

Golgi Apparatus (Golgi Body)

• Receives proteins from the ER.
• Customizes proteins by folding them into usable shapes or adding materials like lipids or carbohydrates.

Vacuoles

• Sac-like structures for storage.
• 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, involved in cellular respiration.
• Produce ATP molecules for cell energy.
• More mitochondria in cells that require more energy.

Cytoskeleton

• Maintains cell shape.
• Includes microfilaments (thread-like, protein) and microtubules (thin hollow tubes).

Unique Organelles in Plant Cells

• Chloroplasts: Where photosynthesis occurs.
  • Contain green pigment chlorophyll.
• Cell Wall: Provides shape, support, and protection.
  • Only found in plant cells; animal cells do not have a cell wall.

Unique Structures in Some Cells

• Cilia: Microscopic hair-like projections in human respiratory tract cells that help trap and expel particles.
• Flagella: Tail-like structures that help some cells move.
  • Found in some bacteria; the only human cell with a flagellum is a sperm cell.

Summary

• Eukaryotic cells: Plant and animal cells with nuclei and membrane-enclosed organelles.
• Prokaryotic cells: Unicellular organisms without these structures.
• All cells consist of a cell membrane, cytoplasm, and genetic material.
• Both plant and animal cells have mitochondria; only plant cells have chloroplasts.