ABSTRACT
Natural nucleic acids (deoxyribonucleic acid [DNA], and ribonucleic acid [RNA]) are macromolecules composed of nucleotide chains. Nucleotides consist of a sugar ring (deoxyribose in DNA and ribose in RNA), a phosphate group, and a nucleic acid ring (which contains a basic nitrogen group and hence is the base in the nucleotide). These nucleotides form phosphodiester bonds between the 3′ group of one sugar molecule and 5′ group of another. The sugar-phosphate backbone does not change, but the base group can be different throughout the chain. There are four nucleic acid bases in DNA nucleotides, to give four different nucleotides: adenine, cytosine, guanine, and thymine. Similarly, there are four nucleic acid bases in RNA, to give four different nucleotides: adenine, cytosine, guanine, and uracil. The bases can be either a purine (adenine or guanine) or a pyrimidine (thymine, cytosine, or uracil). DNA is a double helix and has two complementary antiparallel strands, whereas RNA is, in many of its biological roles, single stranded. The role of nucleic acids (NAs) in nature is of tremendous importance since they are responsible for carrying genetic information from one generation to another. Passage of the genetic information is done by Watson-Crick base pair recognition of complementary strands. Each adenine in one strand makes two hydrogen bonds with thymine (or uracil) in the complementary strand,
CONTENTS
8.1 Introduction ................................................................................................ 231 8.2 Nucleic Acid Hybridization Biosensors .................................................. 232 8.3 Aptamer-Based Biosensor ........................................................................234 8.4 DNAzyme-and Aptazyme-Based Biosensor ........................................235 8.5 DNA-Based Biosensor for Toxicity Evaluation ...................................... 237 8.6 Conclusion .................................................................................................. 240 References ............................................................................................................. 241
and each guanine makes three hydrogen bonds with cytosine. Additionally, the DNA sequence is matched with its complementary sequence in RNA, which is further used to make a protein that satises the genetic code. The process of building the RNA from the DNA is called transcription, whereas the process of building the protein based on the RNA is called translation.
