Bacterial DNA is referred to as naked because it is not associated with:
- (a)any scaffold
- (b)proteins
- (c)ribozymes
- (d)plasmid
Correct — B, proteins. In a eukaryotic cell the long DNA molecule is wound around histone proteins to form nucleosomes and packed into chromatin, so it is never bare. Bacteria, being prokaryotes, lack these histone proteins, so their single circular chromosome sits in the cytoplasm essentially uncoated — which is exactly why it is described as 'naked' DNA. Because the partner it lacks is the protein coat, option (b) is correct.
- (a)any scaffold — Scaffold-like proteins do help loop and fold the bacterial nucleoid, so DNA is not simply free of any scaffold; and 'naked' specifically contrasts with the histone-protein coat of eukaryotic chromatin, not with a scaffold.
- (c)ribozymes — Ribozymes are catalytic RNA molecules; they play no part in packaging DNA, so their presence or absence has nothing to do with DNA being called 'naked'.
- (d)plasmid — A plasmid is a small, separate circular DNA molecule many bacteria carry in addition to the main chromosome. It is itself DNA, not a packaging protein, so DNA being 'naked' is unrelated to plasmids.
DNA packaging differs sharply between prokaryotes and eukaryotes. In a eukaryotic cell, DNA wraps around histone proteins to form nucleosomes that coil into chromatin inside a membrane-bound nucleus. A bacterium has no nucleus and no histone packaging, so its single circular chromosome lies free in a cytoplasmic region called the nucleoid and is described as 'naked' DNA.
The trap is to pick 'plasmid', because plasmids are strongly linked with bacteria, or 'any scaffold', because both sound structural. But the word 'naked' is a comparison with eukaryotic chromatin, whose defining feature is the histone-protein coat. Ask what eukaryotic DNA has that bacterial DNA lacks, and the answer is the histone proteins.
- In eukaryotes, DNA winds around histone proteins to form nucleosomes, the repeating units of chromatin.
- Bacterial DNA is a single circular molecule lying in the nucleoid, with no surrounding nuclear membrane.
- Because it lacks the histone packaging of eukaryotes, prokaryotic DNA is described as 'naked'.
- Bacteria do carry some nucleoid-associated proteins (such as HU) that help fold the chromosome, but these are not the histones that define eukaryotic chromatin.
The word 'naked' means bacterial DNA lacks the histone-protein coat of eukaryotic chromatin, so the missing partner is proteins.
- Choosing 'plasmid' because plasmids are associated with bacteria — plasmids are extra DNA, not a packaging protein.
- Thinking bacterial DNA has no proteins at all; it does carry nucleoid-associated proteins, just not the histones of eukaryotes.
- Confusing the nucleoid (the DNA-containing region of a bacterium) with a true membrane-bound nucleus.
A single-best-answer on why prokaryotic DNA is called 'naked' — link it to the absence of histone-protein packaging.
Which organelle in the cell, other than nucleus, contains DNA?
- (a) Centriole
- (b) Golgi apparatus
- (c) Lysosome
- (d) Mitochondrion
Answer(d) Mitochondrion — mitochondria carry their own circular DNA, a relic of their bacterial (prokaryotic) ancestry.
Mitochondrial DNA is circular and naked like the bacterial chromosome in this NDA question — a direct echo of prokaryotic DNA organisation and its endosymbiotic origin.
- practice — not a real PYQ
In eukaryotic cells, DNA is packaged by wrapping around which proteins to form nucleosomes?
- (a)Histones
- (b)Actin
- (c)Keratin
- (d)Collagen
Answer(a) Histones — DNA coils around histone proteins to form nucleosomes, the repeating units of chromatin.
- practice — not a real PYQ
The region of a bacterial cell where the circular DNA is located is called the:
- (a)Nucleus
- (b)Nucleolus
- (c)Nucleoid
- (d)Ribosome
Answer(c) Nucleoid — bacteria have no membrane-bound nucleus; the naked circular DNA lies in a region called the nucleoid.