One turn of the helix in a B-form DNA is approximately:
Correct answer: D. 3.4 nm
- A. 2 nm
- B. 20 nm
- C. 0.34 nm
- D. 3.4 nm
Explanation
DNA is the largest macromolecule made of helically twisted two antiparallel polydeoxyribonucleotide strands held together by hydrogen bonds. The two strands of DNA are together called a DNA duplex. They have a diameter of 20Å. One turn of a spiral has a distance of 34Å. It contains 10 deoxyribonucleotides in each strand, so that the distance between two adjacent nucleotides is 3.4 Å.
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Chromosomes are DNA-protein structures that carry genes and become visible during cell division. Coverage includes chromatin, centromeres, sister chromatids, homologous chromosomes, chromosome number, and the distinction between diploid and haploid cells, with links to DNA replication, mitosis and meiosis.
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