A1.2 核酸（分子）：练习题

Which of the following components is not found in a DNA nucleotide?

The phosphodiester bond links the phosphate group of one nucleotide to which specific carbon atom of the pentose sugar of the next nucleotide?

While the canonical B-form DNA is right-handed, certain sequences, particularly those with alternating purine-pyrimidine repeats, can transiently adopt the Z-form. What key structural feature distinguishes Z-DNA from B-DNA?

Which base pairs with Adenine in a DNA molecule?

Why is RNA generally considered less stable and more reactive than DNA?

State the specific name of the sugar found in a DNA nucleotide and identify the chemical group located at the 5' carbon position of this sugar.

Explain why the antiparallel orientation of the two strands is crucial for the proper formation and stability of the DNA double helix.

The deamination of cytosine naturally produces uracil. Explain why the presence of thymine instead of uracil in DNA provides a significant evolutionary advantage in terms of genetic stability and repair.

In a double-stranded DNA sample extracted from a specific organism, $18\%$ of the bases are Cytosine (C).

a) Calculate the percentage of Adenine (A) bases present in this DNA sample.

b) Explain the chemical basis for the observation that the amount of Guanine equals the amount of Cytosine, referencing the structure of the DNA double helix.

Eukaryotic DNA is highly organized within the nucleus.

a) Describe the structure of a nucleosome, including the components involved.

b) Explain the role of nucleosomes and subsequent folding processes in the efficient packaging of the long linear DNA molecules within the confines of the eukaryotic nucleus.