Video Transcript
DNA from different sources can be
combined, or hybridized, in a series of steps. In this process, how are the
hydrogen bonds between the two strands of DNA broken? (A) By heating the DNA to a high
temperature, 95 to 100 degrees Celsius. (B) By rapidly cooling the DNA to a
low temperature, five to 10 degrees Celsius. (C) By using the enzyme DNA
polymerase. (D) By using restriction
enzymes. Or (E) by physically forcing the
two strands apart.
This question asks about the
process of DNA hybridization. So let’s review the steps involved
in this process.
DNA hybridization is the process of
two distinct DNA strands separating and then recombining. This recombination often happens
with complementary DNA strands from a different source. You might remember that the two
strands of DNA are connected by hydrogen bonds between nucleotide base pairs. Cytosine and guanine are held
together with three hydrogen bonds, while adenine and thymine are held together with
two.
In order to separate the two
strands of DNA into single strands, these hydrogen bonds must be broken. Because hydrogen bonds are much
weaker than the phosphodiester bonds holding the sugar–phosphate backbone together,
this can be done fairly easily. Hydrogen bonds are destroyed when
the DNA is heated to a high temperature. This results in a single strand of
DNA. Provided a second complementary DNA
strand is present, the DNA can recombine once it has cooled down to form a
double-stranded DNA molecule.
Now that we have discussed the role
of heating in DNA hybridization, we are able to answer our question correctly. The correct answer to the question
“How are the hydrogen bonds between the two strands of DNA broken?” is answer choice
(A): by heating the DNA to a high temperature, 95 to 100 degrees Celsius.
