Class 12 · Molecular Basis of Inheritance

Nucleoid Structure & DNA Organization — NEET Biology

✅ Asked in NEET 2023
📖 NCERT Source

In prokaryotes, such as, E. coli, though they do not have a defined nucleus, the DNA is not scattered throughout the cell. DNA (being negatively charged) is held with some proteins (that have positive charges) in a region termed as 'nucleoid'. The DNA in nucleoid is organised in large loops held by proteins.

🖼️Related NCERT figure: Diagram showing nucleosome structure with DNA wrapped around H1 histone and core histone molecules forming a histone octamer (Figure 5.4a Nucleosome)
NCERT Biology · Class 12 · Chapter 5 · Paragraph 19
How NTA Uses This Concept

In prokaryotes like E. coli, DNA is organized in the nucleoid region through electrostatic interactions: negatively charged DNA binds to positively charged proteins, forming large supercoiled loops. NTA tests this because students often confuse nucleoid with nucleus or assume prokaryotic DNA is randomly scattered. The common mistake is forgetting that proteins actively organize prokaryotic DNA despite the absence of a membrane-bound nucleus. To score correctly, remember: nucleoid = protein-organized DNA loops held by ionic charges, NOT a nucleus, and this organization is essential for gene regulation and DNA replication in prokaryotes.

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QuestionNEET 2023

Given below are two statements: (NEET 2023) Statement I: In prokaryotes, the positively charged DNA is held with some negatively charged proteins in a region called nucleoid. Statement II: In eukaryotes, the negatively charged DNA is wrapped around the positively charged histone octamer to form nucleosome.

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