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#DNA double helix

3 public questions tagged with this topic.

Nucleosome Packing

Diameter of DNA double helix is:

B-form DNA double helix diameter measured by Franklin Wilkins X-ray diffraction patterns approximates 2.0 nanometers, corresponding to distance across base pair plus phosphate backbone van der Waals radii. This baseline dimension explains how 147 base pairs wrapped around 11 nanometer octamer achieves first level compaction. Subsequent levels: nucleosome 11 nanometer, solenoid 30 nanometer, looped scaffold 300 nanometer, metaphase chromatid 700 nanometer represent stepwise coiling. Recognizing 2 nanometer starting point underscores approximately seven-fold linear compaction achieved at nucleosome level alone before higher-order scaffolding multiplies packing ratio toward functional chromosome formation during mitosis.

Ref: Watson and Crick 1953 Nature; Alberts et al., Molecular Biology of the Cell, Chapter 4: DNA Double Helix 2 nm Diameter

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Chemical Bonding

Which of the following interactions contributes least to the stability of a DNA double helix?

London dispersion forces accurately identifies the binding site, binding partner, or molecular interaction described in this question. In Chemical Bonding, molecular recognition and binding specificity are governed by complementary shape, charge, and hydrophobic interactions between molecules. London dispersion forces binds at the specified location due to its structural complementarity and specific non-covalent or covalent interactions. The other options (Base stacking interactions, Hydrogen bonding between base pairs, and Covalent bonds in sugar-phosphate backbone) describe binding to different sites, involve different types of molecular interactions, or represent incorrect binding partners.

Ref: Campbell Biology, Urry et al., 12th Ed.

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DNA

Which of the following stabilizes the double helix at high salt concentrations?

Shielding of phosphate charges is the scientifically accurate answer to this question. Within the study of Nucleic Acid, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Shielding of phosphate charges directly address what is being asked. Among the other options, Increase in hydrogen bonds, Covalent modification of bases, and Phosphodiester hydrolysis do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.

Ref: Campbell Biology, Urry et al., 12th Ed.

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