Q29-25E - Organic Chemistry (Mcmurry)

Question

Question: Which of the following base sequences would most likely be recognized by a restriction endonuclease? Explain.

(a) GAATTC 

(b) GATTACA 

(c) CTCGAG

Step-by-Step Solution

Answer

In solution (a), GAATTC will be recognised by the restriction endonuclease.

In solution (b), GATTACA will not be recognised by the restriction endonuclease.

In solution (c), CTCGAG will be recognised by the restriction endonuclease.

Step 1: Introduction

Restriction endonuclease, commonly known as restriction enzyme, is a kind of restriction endonuclease. It is a bacterial protein that aids in the breaking of DNA at certain locations. Restriction endonuclease has a short and particular nucleotide sequence, i.e. (adenine, guanine, cytosine and thymine). These sequences are strewn over the DNA at random. 

Step 2: Explanation for (a).

The given sequence is,

GAATTC

The above nucleotide sequence can be written as,

$5\text{'}$-GAATTC-$3\text{'}$

The inverted palindromic sequence is,

$3\text{'}$-CTTAAG-$5\text{'}$

Thus, the chain is a complement to each other.

Therefore, it will occur in every $4^6=\mathbf{4096}\mathbf{ }\mathbf{\text{bp}}$

Step 3: Explanation for (b).

The given sequence is,

GATTACA

The above nucleotide sequence can be written as,

$5\text{'}$-GATTACA-$3\text{'}$

The inverted palindromic sequence is,

$3\text{'}$-ACATTAG-$5\text{'}$

Because the nucleotide and the palindromic sequence are incompatible. As a result, restriction endonuclease will fail to identify them.

Step 4: Explanation for (c)

The given sequence is,

CTCGAG

The above nucleotide sequence can be written as,

$5\text{'}$-CTCGAG-$3\text{'}$

The inverted palindromic sequence is,

$3\text{'}$-GAGCTC-$5\text{'}$

Thus, the chain is a complement to each other.

Therefore, it will occur in every $4^6=\mathbf{4096}\mathbf{ }\mathbf{\text{bp}}$