Video Transcript
What type of bond forms between
base pairs in DNA to hold the two strands together in a double helix? (A) Glycosidic, (B) hydrogen, (C)
ionic, (D) covalent, or (E) phosphodiester.
This diagram represents the
double-helix structure of DNA. If we zoom in on a small section of
this DNA molecule, we can see that it’s made of individual units that we call
nucleotides. Each nucleotide contains a
base. There are four different possible
bases, as represented by the four different colors you see here. A special type of covalent bond
called a phosphodiester bond forms between nucleotides. These phosphodiester bonds form the
two strands that make up the DNA molecule. But this question is asking us what
bonds form between base pairs to hold the two strands together. So we can rule out (E) because
phosphodiester is not the correct answer.
The bonds that form between base
pairs are hydrogen bonds. As you can see on this diagram, two
hydrogen bonds form between thymine and adenine, which are the names of these two
bases, and three hydrogen bonds form between guanine and cytosine, which are the
names of the other two bases. We have therefore determined that
the type of bond that forms between base pairs in DNA to hold the two strands
together in a double helix is (B) hydrogen.
