The recognition sequences of four Type-II restriction enzymes (RE) are givenbelow. The symbol (↓) indicates the cleavage site. Identify the RE that generatessticky ends.(A) RE1 - 5̍ G↓GATCC 3̍(B) RE2 - 5̍ CTG↓CAG 3̍(C) RE3 - 5̍ CCC↓GGG 3̍(D) RE4 - 5̍ AG↓CT 3̍
Question
The recognition sequences of four Type-II restriction enzymes (RE) are givenbelow. The symbol (↓) indicates the cleavage site. Identify the RE that generatessticky ends.(A) RE1 - 5̍ G↓GATCC 3̍(B) RE2 - 5̍ CTG↓CAG 3̍(C) RE3 - 5̍ CCC↓GGG 3̍(D) RE4 - 5̍ AG↓CT 3̍
Solution 1
The restriction enzymes that generate sticky ends are those that cut the DNA strand in a staggered manner, leaving a few unpaired bases on one strand. These unpaired bases can form hydrogen bonds with their complementary bases on a DNA fragment cut by the same restriction enzyme, hence the term "sticky".
Looking at the given sequences:
(A) RE1 - 5̍ G↓GATCC 3̍ This enzyme cuts between the G and G in the sequence, leaving a 5' overhang (or "sticky end") of ATCC.
(B) RE2 - 5̍ CTG↓CAG 3̍ This enzyme cuts between the G and C in the sequence, leaving a 5' overhang of CAG.
(C) RE3 - 5̍ CCC↓GGG 3̍ This enzyme cuts between the C and G, but since the sequence is the same on both sides of the cut, it leaves blunt ends, not sticky ends.
(D) RE4 - 5̍ AG↓CT 3̍ This enzyme cuts between the G and C, but since the sequence is not the same on both sides of the cut, it leaves blunt ends, not sticky ends.
So, the restriction enzymes that generate sticky ends are RE1 and RE2.
Solution 2
The restriction enzymes that generate sticky ends are those that cut the DNA strand in a staggered manner, leaving a few unpaired bases on one strand. These unpaired bases can form hydrogen bonds with their complementary bases on a DNA fragment cut by the same restriction enzyme, hence the term "sticky".
Looking at the given sequences:
(A) RE1 - 5̍ G↓GATCC 3̍ This enzyme cuts between the G and G in the sequence, leaving a 5' overhang of ATCC. This is a sticky end.
(B) RE2 - 5̍ CTG↓CAG 3̍ This enzyme cuts between the G and C in the sequence, leaving a 5' overhang of CAG. This is a sticky end.
(C) RE3 - 5̍ CCC↓GGG 3̍ This enzyme cuts between the C and G in the sequence, leaving a 5' overhang of GGG. This is a sticky end.
(D) RE4 - 5̍ AG↓CT 3̍ This enzyme cuts between the G and C in the sequence, leaving a 5' overhang of CT. This is a sticky end.
So, all four restriction enzymes (RE1, RE2, RE3, RE4) generate sticky ends.
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