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CASE FILES: BIOCHEMISTRY
A nsw ers
[6.1]
C. The temperature at which the DNA strands separate is dependent
on the number of hydrogen bonds that make up the base pairing.
Since G-C pairs have three hydrogen bonds while A-T pairs only
have two, then the strand that has the greatest number of G-C pairs
will have the higher melting temperature, Tm, which is the tempera-
ture at which half of the base pairs are broken. Interestingly, the
TATA box, the starting point of transcription in eukaryotes, has
weaker bonding.
[6.2]
B. Most of the sequences recognized by restriction endonucleases are
palindromes; that is, they have the same nucleotide sequence on both
strands when read in the 5' to 3' direction. Since choice B has the only
sequence that will be a palindrome when paired with its complemen-
tary strand, it is the most likely to be a site recognized by a restriction
endonuclease (it is the site recognized by the restriction endonuclease
Pst1).
[6.3]
D. A VNTR analysis examines the hypervariable regions of the
human genome. These contain sequences that are repeated in tandem
a variable number of times and the length is unique for each individual.
Because it is DNA fragments that are being analyzed, the Southern
blot is the most appropriate technique to use to separate and detect
these regions. DNA sequencing is too time-consuming to be practical
for forensic analyses. The Northern blot is used to separate and detect
RNA, whereas the Western blot is used for proteins. Allele-specific
oligonucleotide probes are used when testing for the presence of a
genetic mutation that either introduces or removes a restriction site.
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