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How are the two strands of DNA held together?
A
By hydrogen bonds between complementary nitrogenous bases
B
By ionic bonds between sugar molecules
C
By covalent bonds between phosphate groups
D
By peptide bonds between nucleotides
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1
Recall the structure of DNA, which consists of two strands forming a double helix.
Understand that each strand is made up of nucleotides, which include a sugar, a phosphate group, and a nitrogenous base.
Recognize that the sugar and phosphate groups in each strand are connected by covalent bonds, specifically phosphodiester bonds, forming the backbone of each strand.
Focus on how the two strands are held together: the nitrogenous bases from each strand pair with each other through hydrogen bonds, which are weaker than covalent bonds but strong enough to stabilize the double helix.
Identify that these hydrogen bonds occur specifically between complementary bases: adenine pairs with thymine (two hydrogen bonds), and cytosine pairs with guanine (three hydrogen bonds).