Question

The unpaired nucleotides/single-stranded DNA produced by the action of restriction enzymes on plasmid DNA are referred to as?

a. sticky ends

b.blunt ends

c. triple Strand DNA

d.ligases

Answer 1

Ans.

The Answer is (a) Sticky ends

Explanation:

When a certain restriction enzyme digest's a DNA, a short single stranded segment of DNA is obtained with the one strand overhanging the other.These restriction enzyme cuts the DNA in such a way that although the segment obtained lies between the same 2 bases on the opposite strand but is cut at a short distance away from the center of palindromic sequences. This results in single stranded DNA segments that are not paired up with its corresponding nucleotides.Since they are overhanging stretches and can easily re-attach to the other ends,these are known as sticky ends.The stickness of the ends helps the action of DNA ligase enzyme.Example of Restriction enzyme that forms sticky ends - enzyme BamHl.

Let us also understand what other answer options are :

(b) Blunt ends - While most of the restriction enzymes staggerly cuts the DNA to produce ends with single stranded DNA that overhangs, there are some restriction enzymes that produces blunt ends.These enzymes cut at the middle of the target sequence, leaving no overhang to form blunt ended DNA fragments.Since there are no single stranded overhangs in these blund ended fragments to hold the DNA,it is harder to ligate them together. Smal is a blunt cutter restriction enzyme.

(c) Triple Strand DNA - A DNA structure with 3 oligonucleotides that forms a triple helix by winding around each other is what is called as a Triple strand DNA.

(d) Ligases - Ligases are enzymes used for catalysing the joining of two large molecules.In particular DNA ligases joins two newly formed fragments of  DNA pieces that has a matching ends to form a single unbroken molecule of DNA.