In: Biology
Of the following four 15-bp double-stranded DNA sequences, which will have a higher melting temperature? (Note: only one strand is shown here) Choose the single best answer
CCCGCATCGCCATCG
CATCCTAGCGACTAT
CTATACGACATAGCC
AAATGCATACATCTT
Melting point of DNA :-
• This is the temperature, at where double stranded DNA turns into
single stranded DNA by breaking all hydrogen bonds between double
strands.
• The DNA which has high number of hydrogen bonds has higher
melting point.
Number of hydrogen bonds :-
• In double stranded DNA = Three hydrogen bonds present between
guanine and cytosine, two hydrogen bonds present between adenine
and thymine.
• So, now the DNA strand which has more numbers of cytosine-guanine
base pairs, has more numbers of hydrogen bonds and has higher
melting point.
• Here in question only single strand is given so, which single
strand has more number of guanine and cytosine that has more
guanine-cytosine base pairs.
Melting point of DNA ∝ Numbers of hydrogen bonds ∝ Numbers of guanine cytosine base pairs.
So, guanine cytosine base pairs in given DNA strands -
Strand 1 = 11 Guanine and cytosine bases.
Strand 2 = 7
Strand 3 = 7
Strand 4 = 4
Hence, Strand 1 has highest melting point.
Sequence of melting point :-
Strand 1> Strand 2= Strand 3> Starnd 4