Chapter 24, Problem 11P

(a)

Summary Introduction

To describe: The two structural features required by a DNA molecule to maintain a negatively supercoiled state.

Introduction:

Supercoiling is important for packaging of circular DNA molecule referred as closed circular double helix DNA. DNA can be supercoiled in two ways, positive supercoiling and negative supercoiling. Positive supercoiling is the right-handed and double helical form of DNA, while negative supercoiling is the left-handed and double helical form of DNA.

(b)

Summary Introduction

To enlist: Three structural changes that become more favorable when a DNA molecule is negatively supercoiled.

Introduction:

Deoxyribonucleic acid (DNA) is a genetic material which is responsible for passing information from one generation to another. It is a double helical structure which consists of “two parallel strands” made up of nucleotides. A molecule of DNA carries deoxyribose sugar and a backbone of phosphate. Nitrogenous bases present in DNA molecule are adenine, guanine, cytosine and thymine. Three types of DNA that occur are B-form, A-form and Z-form.

(c)

Summary Introduction

To determine: The enzyme that can generate negative superhelicity in DNA with the aid of ATP.

Introduction:

Topoisomerase II or DNA gyrase “reduces supercoiling” in the DNA at replication fork. It causes nick (breaks) in the double helix DNA strands.

(d)

Summary Introduction

To describe: The physical mechanism by which this enzyme acts.

Introduction:

In replication and transcription, DNA gyrase causes relaxing of positive supercoils and possess the ability to add negative supercoils within the DNA.