Question

DNA fragments are

• A. Neutral
• B. Either positively or negatively charged depending on their size
• C. Negatively charged
• D. Positively charged

Answer 1

The correct option is C Negatively charged

Introduction to structure of DNA
.DNA is a double stranded helical molecule in which each strand is composed of repeating units of deoxyribonucleotides. The adjacent nucleotides are connected by phosphodiester bonds between the 3’OH group of one nucleotide and the 5’ phosphate group of the adjacent one.
.The sugar and phosphodiester bonds form the backbone of each strand and the nitrogenous bases of each strand are projected inwards and form complementary base pairs. Adenine pairs with thymine and cytosine pairs with guanine.

Charge carried by DNA
.DNA is negatively charged due to the presence of the phosphate groups in the sugar phosphate backbone and the free phosphate group present at the 5’ end.
.Each phosphate group participating in the phosphodiester bond formation has one oxygen atom that is negatively charged. These negatively charged oxygen atoms confer an overall negative charge to the DNA strand.

Final answer
(A) Negatively charged