Difference between Prokaryotic and Eukaryotic Cells Lesson

Lesson Overview

• What Is a Prokaryotic Cell?
• What Is a Eukaryotic Cell?
• Characteristics of Prokaryotic and Eukaryotic
• Difference Between Prokaryotic and Eukaryotic Cells
• Prokaryotic and Eukaryotic Cells Assessment

Cells, the fundamental units of life, come in two primary forms: prokaryotic and eukaryotic. Understanding their distinctions is crucial, as these differences underpin the vast diversity of life on Earth. Learning these differences illuminates the evolutionary journey of life and provides insights into cellular function, disease, and biotechnology.

What Is a Prokaryotic Cell?

A prokaryotic cell is a type of cell that lacks a membrane-bound nucleus and other membrane-bound organelles.  Its genetic material, DNA, is located in a region called the nucleoid, which is not enclosed within a membrane. Prokaryotic cells are generally smaller and simpler in structure than eukaryotic cells. 

Fig. 1: A prokaryotic cell, highlighting the cell wall.

What Is a Eukaryotic Cell?

A eukaryotic cell is a type of cell characterized by a membrane-bound nucleus containing its DNA. It also possesses other membrane-bound organelles, such as mitochondria and endoplasmic reticulum, which perform specific cellular functions. Eukaryotic cells are typically larger and more complex than prokaryotic cells. 

Fig. 2: A eukaryotic cell, showing key organelles.

Characteristics of Prokaryotic and Eukaryotic

Prokaryotic and eukaryotic cells, while both fundamental to life, exhibit significant differences in their structure and organization. 

Prokaryotic Cell Characteristics:

• No Nucleus: DNA is located in a nucleoid region, not enclosed by a membrane. This is the defining feature.
  • Explanation: Lack of compartmentalization of genetic material.
  • Example: Bacteria like E. coli.
    
• No Membrane-Bound Organelles: Lack mitochondria, endoplasmic reticulum, Golgi apparatus, etc.
  • Explanation: Simpler cellular organization; metabolic processes occur in the cytoplasm.
  • Example: Archaea like methanogens. 
    
• Small Size: Typically 0.1-5 μm in diameter.
  • Explanation: Higher surface area to volume ratio, facilitating nutrient uptake and waste removal. 
    
• Cell Wall (Usually): Provides structural support and protection. Composition varies (peptidoglycan in bacteria).
  • Explanation: Rigidity and shape maintenance.  
  • Example: Bacterial cell wall made of peptidoglycan. 
    
• Simple Structure: Relatively less complex internal organization.
  • Explanation: Efficient for rapid reproduction and adaptation. 
    
• Circular DNA: Single, circular chromosome located in the nucleoid.
  • Explanation: Different mechanism of gene regulation compared to eukaryotes.
    
• Plasmids (Often): Small, circular DNA molecules separate from the main chromosome.
  • Explanation: Can carry genes for antibiotic resistance or other advantageous traits. 
    
• 70S Ribosomes: Smaller ribosomes compared to eukaryotes.
  • Explanation: Difference in protein synthesis machinery.
    
• Binary Fission: Asexual reproduction.
  • Explanation: Rapid and efficient population growth. 
    
• Examples: Bacteria and Archaea.  

Eukaryotic Cell Characteristics:

• Nucleus Present: DNA enclosed within a membrane-bound nucleus.
  • Explanation: Compartmentalization and protection of genetic material.
  • Example: Nucleus in a human liver cell. 
    
• Membrane-Bound Organelles: Contain mitochondria, ER, Golgi, lysosomes, peroxisomes, and (in plants) chloroplasts.
  • Explanation: Specialized compartments for various cellular functions.  
  • Example: Mitochondria for cellular respiration. 
    
• Larger Size: Typically 10-100 μm in diameter.
  • Explanation: More complex internal organization allows for larger size.
    
• Cell Wall (In some): Present in plants (cellulose) and fungi (chitin), absent in animals.
  • Explanation: Provides structural support and protection.
  • Example: Cell wall of a plant cell made of cellulose. 
    
• Complex Structure: Highly organized internal structure with a cytoskeleton (microtubules, microfilaments).
  • Explanation: Support, cell movement, and intracellular transport.
    
• Linear DNA: Multiple linear chromosomes within the nucleus.
  • Explanation: More complex gene regulation and organization.
    
• 80S Ribosomes: Larger ribosomes compared to prokaryotes.
  • Explanation: Difference in protein synthesis machinery.
    
• Mitosis/Meiosis: Cell division for growth and sexual reproduction.
  • Explanation: Precise duplication and distribution of chromosomes.
  • Examples: Protists, Fungi, Plants, and Animals.

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Prokaryotic and Eukaryotic Cells

Difference Between Prokaryotic and Eukaryotic Cells

Prokaryotic and Eukaryotic cells distinctions reflect their evolutionary history and have profound implications for the diverse functions they perform.  

Fig. 3: Showing side-by-side comparison of prokaryotic (gram-negative bacteria) and eukaryotic (animal) cell structures, labeling key organelles and features.

Prokaryotic and Eukaryotic Cells Assessment

I. Fill in the Blanks:

1. Prokaryotic cells lack a membrane-bound __________, while eukaryotic cells have a true __________.  
2. The genetic material in prokaryotes is typically __________, while in eukaryotes it is __________.
3. __________ are smaller in prokaryotes (70S) compared to eukaryotes (80S).
4. __________ cells are generally smaller and simpler in structure than __________ cells.
5. __________ is a unique component of bacterial cell walls, not found in eukaryotic cell walls.
6. Eukaryotic cells possess membrane-bound __________, such as mitochondria and endoplasmic reticulum, which are absent in prokaryotes.
7. Prokaryotes primarily reproduce through __________, while eukaryotes can reproduce both sexually and __________.
8. __________ cells include bacteria and archaea, while _________ cells comprise protists, fungi, plants, and animals.
9. __________ is a network of protein filaments that provides structural support and facilitates cell movement in eukaryotes.  
10. Besides the main chromosome, prokaryotic cells may also contain small circular DNA molecules called __________.  

Answers: 

I. Fill in the Blanks:

1. nucleus, nucleus
2. circular, linear
3. Ribosomes
4. Prokaryotic, eukaryotic
5. Peptidoglycan
6. organelles
7. binary fission, asexually
8. Prokaryotic, eukaryotic
9. Cytoskeleton
10. plasmids