Q20.1-2CC. - Campbell Biology

Question

One strand of DNA molecule has the following sequence:    

5’-CTTGACGATCGTTACCG-3’

Draw the other strand. Will PvuI (see question I) cut this molecule? If so, draw the products.

Step-by-Step Solution

Answer

The DNA sequence of both strands would be:

 

 $\begin{array}{c}5’-CTTGACGATCGTTACCG-3’\\ 3’-GAACTGCTAGCAATGGC-5’\\ \end{array}$

Yes, PvuI can cut the given DNA sequence. The products of the cleavage are:

 

$\begin{array}{c}5’-CTTGACGAT-3’\\ 3’-GAACTGC-5’\\ \end{array}$ +        $\begin{array}{c}5’-GTTACCG-3’\\ 3’- TAGCAATGGC-5’ \\ \end{array}$

Step 1: Structure of DNA

DNA comprises two strands running in opposite directions. One runs in 5’ to 3’ while the other runs in 3’ to 5’ direction. The two strands of DNA are complementary to each other and bonded through hydrogen bonds.

 

In DNA, thymine (T) base pairs with adenine (A) and cytosine (C) base pairs with guanine (G). Thus, the DNA sequence of the other strand is $3’-GAACTGCTAGCAATGGC-5\text{'}$.

The sequence of the DNA molecule would be  $\begin{array}{c}5’-CTTGACGATCGTTACCG-3’\\ 3’-GAACTGCTAGCAATGGC-5’\\ \end{array}$.

 

Step 2: Pvu I cuts the DNA molecule

The restriction enzyme PvuI recognizes 5’-CGATCG-3’ on both strands of DNA. This restriction site is present in the given DNA sequence. Therefore, PvuI recognizes the restriction site and cuts the DNA molecule within the restriction site.

Step 3: Products of Pvu I cleavage

PvuI recognizes its restriction site and cleaves the sugar-phosphate covalent bond between the T and C on each strand. As a result, two fragments of DNA with staggering ends are produced.

 

 $\begin{array}{c}5’-CTTGACGAT-3’\\ 3’-GAACTGC-5’\\ \end{array}+\begin{array}{c}5’-GTTACCG-3’\\ 3’- TAGCAATGGC-5’\\ \end{array}$