Chapter 13, Problem 20A

a)

Summary Introduction

To determine:

Lane in gel electrophoresis that depicts recombinant DNA.

Introduction:

The technique of separating DNA fragments based on their size is termed as gel electrophoresis. In this technique, DNA samples are added to well at the end of the gel. Then, electric current is applied through the gel. As DNA is negatively charged, DNA fragments go towards the positive electrode.

Answer to Problem 20A

Third lane contains recombinant DNA.

Explanation of Solution

As recombinant DNA is formed by combination of plasmid DNA and DNA fragment, the mass of recombinant DNA would be high. In gel electrophoresis, DNA fragments with higher mass move slowly towards the end of the gel as compared to with low mass. So, recombinant DNA being high in mass will flow slowly through the gel and hence, will be seen near top of gel. Hence, recombinant DNA is in third lane of gel.

b)

Summary Introduction

To determine:

Lane corresponding to plasmid.

Introduction:

The technique of separating DNA fragments based on their size is termed as gel electrophoresis. In this technique, DNA samples are added to well at the end of the gel. Then, electric current is applied through the gel. As DNA is negatively charged, DNA fragments go towards the positive electrode.

Answer to Problem 20A

First lane corresponds to plasmid.

Explanation of Solution

As recombinant DNA is formed by combination of plasmid DNA and DNA fragment, the mass of recombinant DNA would be high. In gel electrophoresis, DNA fragments with higher mass move slowly towards the end of the gel as compared to with low mass. So, plasmid will move fast at the end of gel as compared to recombinant fragment gel and is seen at level below recombinant DNA. Hence, plasmid is found in first lane of gel.

c)

Summary Introduction

To determine:

Lane that shows DNA fragments that formed by cleavage done by restriction enzymes.

Introduction:

The technique of separating DNA fragments based on their size is termed as gel electrophoresis. In this technique, DNA samples are added to well at the end of the gel. Then, electric current is applied through the gel. As DNA is negatively charged, DNA fragments go towards the positive electrode.

Answer to Problem 20A

Second lane represents cleaving using a restriction enzyme of the recombinant DNA molecule.

Explanation of Solution

Restriction enzymes cleave the DNA strand at a particular site and form two different DNA fragments, that can be similar or different in size. In the second lane, there are two DNA fragments, this means, in the well along with the DNA, restriction enzyme was also added, that cleaved the DNA into small fragments.