ii. Prokaryotic vs. eukaryotic cells – EduRise Entry Test Experts

Topic: Prokaryotic vs. Eukaryotic Cells

The two fundamental blueprints of life.

1. Core Concepts: The Two Types of Cells

Prokaryotic Cells: The Simple Pioneers

The name "prokaryote" comes from Greek: pro (before) and karyon (nut or kernel), meaning "before nucleus." These are the simplest and most ancient types of cells.

Analogy: Think of a prokaryotic cell as a one-room studio apartment. Everything is in a single, open space. The bed (DNA) is in the main room, not in a separate bedroom.

No Nucleus: Their genetic material (a single, circular DNA molecule) floats in a region called the nucleoid. It is not enclosed by a membrane.
No Membrane-Bound Organelles: They lack complex, membrane-enclosed structures like mitochondria, endoplasmic reticulum, or a Golgi apparatus.
Ribosomes: They have ribosomes (for making proteins), but they are smaller (70S) than those in eukaryotes.
Size: They are very small, typically 0.1–5.0 micrometers in diameter.
Examples: Bacteria and Archaea.

Eukaryotic Cells: The Complex Organizers

"Eukaryote" means "true nucleus" (eu = true). These cells are larger, more complex, and make up all multicellular organisms, including us.

Analogy: A eukaryotic cell is like a large mansion with many specialized rooms. The important blueprints (DNA) are safely stored in the master office (the nucleus), the power is generated in the power plant (mitochondria), and there's a factory and shipping center (ER and Golgi).

True Nucleus: Their genetic material (multiple, linear DNA molecules) is well-protected inside a double membrane-bound nucleus.
Membrane-Bound Organelles: They are full of specialized compartments (organelles) like mitochondria, ER, Golgi, lysosomes, etc., each performing a specific job. This is called compartmentalization.
Ribosomes: Their ribosomes are larger (80S).
Size: They are much larger, typically 10–100 micrometers in diameter.
Examples: Animals, Plants, Fungi, and Protists.

2. Visualizing the Cells

Prokaryotic Cell

Simple structure with a nucleoid region for DNA and no internal compartments.

Eukaryotic Cell (Animal)

Complex structure with a true nucleus and membrane-bound organelles.

3. 🧠 Medical Case Study: Antibiotic Action

A patient presents with a severe sore throat, fever, and swollen lymph nodes. A throat swab confirms a diagnosis of strep throat, caused by the bacterium Streptococcus pyogenes. The doctor prescribes a course of antibiotics (e.g., penicillin).

Question: Why is this antibiotic effective against the bacteria but harmless to the patient's own cells?

Answer & Explanation (Selective Toxicity):

The effectiveness of antibiotics relies on the fundamental differences between prokaryotic (bacterial) and eukaryotic (human) cells. This principle is called selective toxicity.

Targeting the Cell Wall: Penicillin works by inhibiting the formation of peptidoglycan, a crucial component of the bacterial cell wall. Since human (eukaryotic) cells do not have a cell wall, the drug has no target and causes no harm.
Targeting Ribosomes: Other antibiotics, like erythromycin or tetracycline, target the smaller 70S ribosomes found in bacteria. They disrupt protein synthesis, killing the bacteria. Human cells have larger 80S ribosomes, which are unaffected by these drugs.
Takeaway: Understanding the structural differences between prokaryotic and eukaryotic cells is not just academic; it is the foundation for developing life-saving medicines that can specifically target pathogens without harming the host.

4. 📊 Concept Check: True or False?

Score: 0 / 4

5. 📝 IMAT-Style Practice Questions

Question 1: Which of the following structures is found in eukaryotic cells but is absent in prokaryotic cells?

A. Plasma membrane

B. Ribosomes

C. DNA

D. Mitochondrion

E. Cytoplasm

Show Answer & Explanation

Correct Answer: D

Reasoning:

The defining feature of eukaryotes is compartmentalization through membrane-bound organelles. The mitochondrion is a classic example.
Prokaryotes lack all membrane-bound organelles.
Incorrect Options: Both cell types have a plasma membrane (A), ribosomes (B), DNA (C), and cytoplasm (E). These are fundamental components required for any cell to live.

Question 2: A scientist discovers a new microscopic organism. It has a cell wall, a plasma membrane, and its DNA is organized in a single circular chromosome, not enclosed by a membrane. This organism is most likely a:

A. Plant cell

B. Animal cell

C. Fungus

D. Protist

E. Bacterium

Show Answer & Explanation

Correct Answer: E

Reasoning:

The key identifier is the genetic material: a single circular chromosome not enclosed by a membrane. This describes the nucleoid region of a prokaryote.
Of the choices given, only a bacterium is a prokaryote.
Incorrect Options: Plant cells (A), animal cells (B), fungi (C), and protists (D) are all eukaryotes. They have a true nucleus containing multiple linear chromosomes. While plant and fungal cells have cell walls, their internal organization is eukaryotic.

6. 🧾 Key Takeaways Summary

Main Distinction: The presence (Eukaryote) or absence (Prokaryote) of a true, membrane-bound nucleus.
Organelles: Eukaryotes have extensive internal membrane-bound organelles (mitochondria, ER, etc.); prokaryotes do not.
DNA: Eukaryotic DNA is linear and in the nucleus. Prokaryotic DNA is circular and in a nucleoid region.
Ribosomes: Both have ribosomes, but they are larger in eukaryotes (80S) than in prokaryotes (70S) - a key target for antibiotics.
Size & Complexity: Eukaryotes are significantly larger and more structurally complex than prokaryotes.