Multiple Choice
In the context of DNA structure, what type of biomolecule are DNA and RNA?
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7. DNA and Chromosome Structure
DNA Structure
Multiple Choice
In terms of overall electrical charge at physiological pH, what net charge does DNA typically carry and what structural feature is primarily responsible?
A
Net positive charge due to the amino groups on the nitrogenous bases
B
Net neutral charge because base pairing cancels the charges in the helix
C
Net positive charge due to hydrogen bonding between complementary bases
D
Net negative charge due to the phosphate groups in the sugar-phosphate backbone
Verified step by step guidance1
Understand that DNA is composed of nucleotides, each containing a sugar, a phosphate group, and a nitrogenous base.
Recognize that at physiological pH (around 7.4), the phosphate groups in the sugar-phosphate backbone lose protons, becoming negatively charged.
Note that the nitrogenous bases do not contribute a net positive charge because their amino groups are not ionized to carry a positive charge at physiological pH.
Realize that base pairing (hydrogen bonding) does not neutralize the overall charge; it only stabilizes the double helix structure.
Conclude that the net charge of DNA is negative due to the presence of negatively charged phosphate groups along the backbone.
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