NDA Biology · Cell Biology

Prokaryotic vs Eukaryotic Cells

Prokaryotic cells (bacteria) have no membrane-bound nucleus — just a 'nucleoid' of naked circular DNA — and no membrane-bound organelles; eukaryotic cells (plants, animals, fungi) have a true nucleus and organelles like mitochondria.

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Why this matters

A tight, high-frequency 5-PYQ cluster, all single-fact recall. The bank tests the same handful of points: prokaryotes lack a true nucleus (they have a nucleoid), lack membrane-bound organelles (no mitochondria), have a single circular chromosome, and their DNA is 'naked' (no histone proteins). All EASY or MODERATE.

Concept 1 of 2

Prokaryote vs eukaryote — the contrast table

Intuition

The whole subtopic rests on one comparison. A eukaryote has a membrane-bound nucleus and organelles; a prokaryote has neither — its DNA sits free as a nucleoid and it has no mitochondria. Anything 'membrane-bound' is the eukaryote's signature.

Definition

The key differences between the two cell types:

Nucleus — eukaryotes have a true membrane-bound nucleus; prokaryotes have only a nucleoid (no membrane).
Organelles — eukaryotes have membrane-bound organelles (mitochondria, ER, Golgi); prokaryotes have none.
Both have a cell wall, plasma membrane and ribosomes — so these do NOT distinguish them.
'Exclusively present in a eukaryote' = the mitochondrion (a membrane-bound organelle).
'NOT present in a prokaryote' = the nucleus (and other membrane-bound organelles).

Both have a wall, membrane and ribosomes. Only the eukaryote has a true nucleus and membrane-bound organelles.

Feature	Prokaryote	Eukaryote
Nucleus	Nucleoid (no membrane)	True membrane-bound nucleus 'Not present in a prokaryote' → the nucleus.
Mitochondria	Absent	Present 'Exclusively in eukaryotes' → mitochondria (membrane-bound).
Cell wall	Present	Present (plants/fungi)
Plasma membrane	Present	Present
Ribosomes	Present (70S)	Present (80S)

Cell wall, plasma membrane and ribosomes are in BOTH — so they can never be the answer to 'what's exclusive / what's missing'. Look for the membrane-bound feature.

Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 1Cell BiologyEASY

Which one of the following structures is not present in a prokaryotic cell?

[Q69 · Apr · 2023]

Cell wall is NOT eukaryote-exclusive

Bacteria (prokaryotes) have a cell wall, so 'cell wall' can never be the answer to 'what is exclusive to eukaryotes'. The eukaryote-only answer is a membrane-bound structure — the nucleus or mitochondria.

Drill 2 more on prokaryote vs eukaryote — the contrast table

Concept 2 of 2

The nucleoid and 'naked' bacterial DNA

Intuition

Because a prokaryote has no nuclear membrane, its DNA floats free in a region called the nucleoid. That DNA is also called 'naked' — it isn't wrapped around histone proteins the way eukaryotic DNA is. And there's just one of it: a single circular chromosome.

Definition

Prokaryotic DNA facts:

The membrane-less region holding the DNA is the nucleoid (not nucleolus, not nucleosome).
Bacterial DNA is called 'naked' because it is NOT associated with histone proteins (eukaryotic DNA is wound around histones).
Most prokaryotes have a single circular chromosome — chromosome number = 1 (plus optional plasmids).

Term	Meaning
Nucleoid	The membrane-less DNA region of a prokaryote Nucleoid — not nucleolus (eukaryotic) or nucleosome (DNA+histone unit).
'Naked' DNA	Bacterial DNA NOT bound to histone proteins 'Naked because not associated with' → proteins (histones).
Chromosome number	Usually 1 (a single circular chromosome)

Practice this conceptself-check · 3 quick reps

From the bank · past-year question

Example 2Cell BiologyEASY

Bacterial DNA is referred to as naked because it is

\textbf{\text{not}}

associated with :

[Q122 · Apr · 2024]

Nucleoid vs nucleolus vs nucleosome

The prokaryotic DNA region is the NUCLEOID. The nucleolus (makes ribosomes) and the nucleosome (DNA wound on histones) are EUKARYOTIC structures — both are distractors here.

Drill 1 more on the nucleoid and 'naked' bacterial dna

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Prokaryote vs eukaryote — the contrast table5 rows

Feature	Prokaryote	Eukaryote
Nucleus	Nucleoid (no membrane)	True membrane-bound nucleus 'Not present in a prokaryote' → the nucleus.
Mitochondria	Absent	Present 'Exclusively in eukaryotes' → mitochondria (membrane-bound).
Cell wall	Present	Present (plants/fungi)
Plasma membrane	Present	Present
Ribosomes	Present (70S)	Present (80S)

Cell wall, plasma membrane and ribosomes are in BOTH — so they can never be the answer to 'what's exclusive / what's missing'. Look for the membrane-bound feature.

The nucleoid and 'naked' bacterial DNA3 rows

Term	Meaning
Nucleoid	The membrane-less DNA region of a prokaryote Nucleoid — not nucleolus (eukaryotic) or nucleosome (DNA+histone unit).
'Naked' DNA	Bacterial DNA NOT bound to histone proteins 'Naked because not associated with' → proteins (histones).
Chromosome number	Usually 1 (a single circular chromosome)

Watch out for (2)

Cell wall is NOT eukaryote-exclusive
→ Prokaryote vs eukaryote — the contrast table
Nucleoid vs nucleolus vs nucleosome
→ The nucleoid and 'naked' bacterial DNA

Drill every past-year question on this subtopic

5 questions from the bank — paginated, with cart and Word-export support.

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