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प्रश्न
Write a note on the packaging of DNA in prokaryotes.
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उत्तर
- In prokaryotes like E. coli, cell size is almost 2-3 µm long.
- They lack a well-organized nucleus i.e. nucleus is without nuclear membrane and nucleolus.
- The nucleoid is a small, circular, highly folded, naked ring of DNA which is 1100 µm (approximately 1.1 mm) long in perimeter, containing about 4.6 million base pairs.
- The nucleoid is to be packaged into a cell that is approximately 2-3 µm long.
- Hence, the negatively charged DNA becomes circular, reducing the size to 350 µm in diameter. This is further reduced to 30 µm in diameter because of folding/looping. 40-50 domains (loops) are formed.
- The formation of loops is assisted by RNA connectors.
- Each domain is further coiled and supercoiled, thereby reducing the size down to 2 µm in diameter.
- This coiling (packaging) is assisted by positively charged HU (Histone like DNA binding proteins) proteins and enzymes like DNA gyrase and DNA topoisomerase I, for maintaining super coiled state.
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संबंधित प्रश्न
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