Preface

Deoxyribonucleic acid (DNA) is the cornerstone of life. It consists of the sugar ribose, phosphate, and the bases of thymine, cytosine, adenine, and guanine. Among these constructive materials, bases have the most important role in transferring genetic information from one generation to another. Hence, the language of information located on DNA molecules is genetic, which, by the contribution of RNA polymerase, changes into mRNA molecules. By the participation of ribosomes, the mRNAs are then translated into proteins. Thus, the genetic language of DNA is translated into proteins.

There are several cellular, genetic, and environmental factors that can damage DNA molecules. This damage may lead to destructive mutations and lesions predisposing individuals to different infectious diseases, autoimmune diseases, and cancers. As such, there are several DNA repair mechanisms that protect DNA molecules from a variety of damages, lesions, and destructive agents.

DNA modifications can occur spontaneously or via cellular activities such as errors in DNA replication or RNA transcription processes. Moreover, reactive oxygen species (ROS), reactive nitrogen species (RNS), alkylation agents, X-rays, ionizing radiation, and ultraviolet (UV) beams are the most recognized DNA-modifying agents that result in lesions and damages to one or both DNA strands.

In contrast to DNA-modifying agents, there is a wide range of DNA repair mechanisms, such as base excision repair (BER), mismatch repair (MMR), nucleotide excision repair (NER), homologous recombination (HR), and non-homologous end joining (NHEJ) that have evolved in different organisms.

This book is a collection of chapters covering DNA structural bioinformatics, DNA damages and lesions, and related DNA repair mechanisms. The volume is divided into three main sections: "Biochemistry and Bioinformatics," "DNA Damage-Repair Mechanisms," and "DNA Repair: Cancers and Diseases."

The first section consists of Chapter 1: "Where Quantum Biochemistry Meets Structural Bioinformatics: Excited Conformationally-Tautomeric States of the Classical A·T DNA Base Pair." This chapter uses quantum biochemistry and structural bioinformatics to reveal the conformation and configuration of DNA and its base pairs at the quantum level.

The second section includes five chapters: Chapter 2 "Origin of DNA Repair in the RNA World"; Chapter 3 "Super-Resolution Radiation Biology: From Bio-Dosimetry towards Nano-Studies of DNA Repair Mechanisms"; Chapter 4 "DNA Damage and Repair Mechanisms Triggered by Exposure to Bioflavonoids and Natural Compounds"; Chapter 5 "Recent Perspectives in Radiation-Mediated DNA Damage and Repair: Role of NHEJ and Alternative Pathways"; and Chapter 6 "Interstrand Crosslink Repair: New Horizons of DNA Damage Repair."

**II**

**Section 3**

DNA Repair Defects in Sarcomas

*and Vishwa Jyoti Baruah*

*by Huifangjie Li and Jinbin Xu*

Epigenetics and DNA Repair in Cancer

Genomic Instability and DNA Repair in Cancer *by Bhaswatee Das, Bipasha Choudhury, Aditya Kumar* 

The Striatal DNA Damage and Neurodegenerations

DNA Repair: Cancers and Diseases **141**

**Chapter 7 143**

**Chapter 8 167**

**Chapter 9 189**

**Chapter 10 207**

*by Niknam Riyahi, M. Reza Saadatzadeh, Khadijeh Bijangi-Vishehsaraei,* 

*by María José López-Ibarra and Marta Elena Hernández-Caballero*

*Farinaz Barghi, Pankita H. Pandya and Karen E. Pollok*

The third section includes four chapters: Chapter 7 "DNA Repair Defects in Sarcomas"; Chapter 8 "Epigenetics and DNA Repair in Cancer"; Chapter 9 "Genomic Instability and DNA Repair in Cancer"; and Chapter 10 "The Striatal DNA Damage and Neurodegenerations."

This book is the result of collaboration and cooperation among numerous experts in the field. I am sincerely grateful for their contributions. I would also like to thank Ms. Mia Vulovic, Lucija Tomicic-Dromgool, and Martina Usljebrka Kauric at IntechOpen for their support and cooperation during the preparation of this valuable book.
