Question

Which of the following sequences in double-stranded DNA is most likely to be recognized as a cutting site for a restriction enzyme?

(A) AAGG

TTCC

(B) GGCC

CCGG

(C) ACCA

TGGT

(D) AAAA

TTTT

Short answer

(A) The option “AAGG-TTCC” is false.

(B) The option “GGCC-CCGG” is true.

(C) The option “ACCA-TGGT” is false.

(D)The option “AAAA-TTTT” is false.

Step-by-step solution

Step 1: Restriction Enzyme

Restriction enzymes are types of endonucleases that cut DNA molecules at specific sites to get the DNA fragments. They are divided into five types on the basis of the site of restriction.

They break double-stranded DNA by making breaks in both strands in the backbones. So they are important tools in recombinant DNA technology.

Explanation of option ‘(A)’

Restriction enzymes cleave the DNA at their recognition sequences that are called restriction sites that are generally symmetrical. The sequence has a similar nucleotide sequence when read in the same orientation.

Thus, AAGG-TTCC is not a symmetrical sequence.

Therefore, the given option is false.

Explanation of option ‘(B)’

When the first strand is read in 5’ to 3’ direction, it is GGCC, and when the second strand is read in 5’ to 3’ direction, it is also GGCC. So it is a symmetrical sequence.

Thus, the sequence given in the option can be recognized by restriction enzymes.

Therefore, the given option is true.

Explanation of option ‘(C)’

When the first strand is read in 5’ to 3’ direction, it is ACCA, and when the second strand is read in 5’ to 3’ direction, it is TGGT. The sequences in both strands are different, so it is not a symmetrical sequence.

Thus, the restriction enzyme only cuts the symmetrical sequences.

Therefore, the given statement is false.

Explanation of option ‘(D)’

Restriction enzyme only cuts at the restriction sites that have palindromic or symmetrical sequences.

Thus, the sequence mentioned in the option is not symmetrical.

Therefore, the given statement is false.