DNA Packaging Flashcard (PDF)

Anil birla sir Learning objective: DNA packaging (NCERT page no. 83) Questions Answers 1. What is the distance The distance is approximately 0.34 nm between two consecutive (0.34×10–9 m). base pairs in DNA? 2. How long is the DNA It is approximately 2.2...

Anil birla sir Learning objective: DNA packaging (NCERT page no. 83) Questions Answers 1. What is the distance The distance is approximately 0.34 nm between two consecutive (0.34×10–9 m). base pairs in DNA? 2. How long is the DNA It is approximately 2.2 metres long. double helix in a typical mammalian cell? 3. How is such a long The DNA is packaged with the help of polymer packaged in a proteins into a compact, organized cell? structure. 4. What is the length of E. The length of E. coli DNA is 1.36 mm. coli DNA? 5. How is DNA organized in In prokaryotes, DNA is held with some prokaryotes like E. coli? proteins in a region termed as ‘nucleoid’. The DNA in nucleoid is organised in large loops held by proteins. 6. How is DNA organized in In eukaryotes, DNA is wrapped around a set eukaryotes? of positively charged proteins called histones to form a structure called a nucleosome. 7. What are histones? Histones are a set of positively charged, basic proteins that are rich in the basic amino acid residues lysine and arginine. 8. What is a histone A histone octamer is a unit of eight octamer? histone molecules. 9. What is a nucleosome? A nucleosome is a structure formed by DNA wrapped around a histone octamer. A typical nucleosome contains 200 bp of DNA helix. 10. What is chromatin? Chromatin is a structure in the nucleus formed by nucleosomes. It appears as ‘beads- on-string’ structure under an electron microscope. Anil birla sir 11. How many nucleosomes The exact number can vary, but it’s in the are present in a millions given the length of DNA in a mammalian cell? mammalian cell. 12. How is the ‘beads-on- The structure is packaged to form chromatin fibers that are further coiled string’ structure in and condensed at metaphase stage of cell chromatin packaged to division to form chromosomes. form chromosomes? 13. What proteins are required The packaging of chromatin at higher level for higher level requires an additional set of proteins that packaging of chromatin? are collectively referred to as non-histone chromosomal (NHC) proteins. 14. What is the role of non- Non-histone chromosomal proteins play a histone chromosomal crucial role in maintaining the structure proteins? of the chromosomes and regulation of gene activity. 15. What is the charge on DNA DNA is negatively charged due to the and why? phosphate groups in its backbone. 16. Why are histones Histones are positively charged due to the positively charged? presence of basic amino acid residues lysine and arginine. 17. How does the charge on The negatively charged DNA is attracted to DNA and histones the positively charged histones, allowing facilitate their the DNA to wrap around the histones and interaction? form nucleosomes. 18. What happens to the During cell division, the chromatin fibers chromatin during cell coil and condense to form chromosomes. division? Non-histone chromosomal proteins are a set of proteins that play a crucial role in 19. What are Non-histone maintaining the structure of the Chromosomal (NHC) chromosomes and regulation of gene proteins? activity. Euchromatin is a region of chromatin that is loosely packed and stains light. It is said to be transcriptionally active 20. What is euchromatin? chromatin. Anil birla sir Heterochromatin is a region of chromatin that is more densely packed and stains dark. It is said to be transcriptionally 21. What is heterochromatin? inactive. The main difference lies in their structure and function. Euchromatin is 22.What is the difference loosely packed and transcriptionally between euchromatin and active, while heterochromatin is densely heterochromatin? packed and transcriptionally inactive.