Insect Molecular Genetics

An Introduction to Principles and Applications

Marjorie A. Hoy

• Publisher: Academic Press
• Year: 2018
• eBook ISBN: 9780128152317
• Edition: 4
• Topic: Biological Sciences
• Subtopic: Entomology
• Index: Biological Sciences

Insect Molecular Genetics

Part I

Genes and Genome Organization in Eukaryotes

Chapter 1

DNA, Gene Structure and DNA Replication

Abstract

This chapter covers the structure and make-up of Deoxyribonucleic acid (DNA), the various forms DNA can take, its replication via mitosis or meiosis, and the role of DNA in transmitting genetic information. The importance of the double helix structure of DNA is discussed. It goes on to cover the structure of RNA and the ways RNA relates to and differs from DNA. The chapter includes a brief discussion of the history of the study of genetics, the establishment of the “Central Dogma,” and subsequent challenges to that dogma. The section on genes covers the structure, effects, and organization of genes, and the difficulties of defining the nature of genes. The chapter goes on to discuss the fidelity of DNA replication, DNA repair, and mutations in the genome.

Keywords

DNA; RNA; Gene; Replication; Genetic

Chapter Outline

• 1.1 Overview
• 1.2 DNA is the Hereditary Material: A Brief History
• 1.3 The Central Dogma
• 1.4 The “RNA World” Came First?
• 1.5 The Molecular Structure of DNA
• 1.6 The Molecular Structure of RNA
• 1.7 The Double Helix
• 1.8 Complementary Base Pairing is Fundamental
• 1.9 DNA Exists in Several Forms
• 1.10 Genes
• 1.11 The Genetic Code for Protein-Coding Genes is a Triplet and is Degenerate
• 1.12 Gene Organization
• 1.13 Efficient DNA Replication is Essential
• 1.14 DNA Replication is Semiconservative
• 1.15 Replication Begins at Replication Origins
• 1.16 DNA Replication Occurs Only in the 5′ to 3′ Direction
• 1.17 Replication of DNA Requires an RNA Primer
• 1.18 Ligation of Replicated DNA Fragments
• 1.19 DNA Replication During Mitosis in Eukaryotes
• 1.20 Telomeres at the End: A Solution to the Loss of DNA During Replication
• 1.21 DNA Replication Fidelity and DNA Repair
• 1.22 Mutations in the Genome
• 1.23 Common Genetic Terminology
• 1.24 Independent Assortment and Recombination During Sexual Reproduction
• References
• Further Reading

1.1 Overview

Arthropod genes are made of DNA and are located in chromosomes that consist of proteins, RNA, and DNA. DNA is a polymer of nucleotides. Each nucleotide consists of a pentose sugar, one of four nitrogenous bases, and a phosphoric acid component. DNA consists of two complementary strands in a helix form. Pairing of the nitrogenous bases adenine (A) with thymine (T), and cytosine (C) with guanine (G) on the two complementary strands occurs by hydrogen bonding. A pairs with T by two hydrogen bonds, and C pairs with G by three. DNA has chemically distinct 5′ and 3′ ends and the two strands are antiparallel, with one running in the 5′ to 3′ direction and the other in the 3′ to 5′ direction. The antiparallel orientation of the two strands creates a problem when DNA is duplicated or replicated during mitosis or meiosis.

Genetic information in protein-coding genes is determined by the sequence of nitrogenous bases (A, T, G, C) in one of the strands, with a three-base (triplet) codon designating an amino acid. The genetic code is degenerate, which means that more than one codon specifies most amino acids. The genetic information is expressed when DNA is transcribed into pre-messenger RNA, which is processed into messenger RNA, which then is translated into polypeptides. Most insect genes have intervening noncoding sequences (introns) that must be removed from the mRNA molecule before translation into the protein can occur.

Efficient and accurate replication of DNA must occur at each cell division or the cell or organism may not survive. DNA replication is semiconservative, which means that one of the nucleotide strands of each new DNA molecule is new and the other is old. The new DNA strand is complementary to the parental (or template) strand. DNA replication occurs in one direction only, from the 5′ to the 3′ end of the strand, and thus replication takes place differently on the two antiparallel strands. Replication on the “leading strand” can occur in the 5′ to 3′ direction in a continuous manner. DNA replication on the “lagging strand” occurs in short segments (Okazaki fragments) because the DNA runs in the 3′ to 5′ direction. Subsequently, the Okazaki fragments must be ligated together. Replication of DNA in chromosomes begins at multiple sites called origins of replication along the chromosome, and involves a number of enzymes and proteins. Although DNA replication is usually highly accurate, errors in DNA replication, or mutations, can result from duplications, deletions, inversions, and translocations of nucleotides, which may affect the functioning of the resultant polypeptide. New combinations of genes can occur through recombination during meiosis.

1.2 DNA is the Hereditary Material: A Brief History

Gregor Johann Mendel founded modern genetics in 1866 by publishing his studies on inheritance in garden peas. He confirmed that hereditary traits were transmitted from generation to generation and proposed the Principles of Segregation and Independent Assortment, which will be discussed further in the description of meiosis and mitosis in Chapter 4. His work, however, was not widely known until 1900, when Hugo de Vries, Carl Correns, and Erich von Tschermak rediscovered these laws of inheritance. Mendel described traits in peas that were “dominant” or “recessive,” and showed that peas could be selected for different traits and were inherited in a stable manner.

The discovery that DNA (deoxyribonucleic acid) is the hereditary material was first determined using a bacterium that causes pneumonia (Streptococcus pneumoniae) (Griffiths, 1928). Prior to this, scientists speculated that the hereditary material might be composed of proteins or RNA. Proteins were considered the most likely hereditary material because they were more variable (having 20 amino acids that could serve as the genetic code) than DNA. Furthermore, proteins are present in the nucleus in amounts nearly equal to DNA. DNA, by contrast, seemed to have only four types of structure (consisting of adenine, thymine, cytosine, or guanine) that could serve as the genetic code. Griffiths (1928) found that nonvirulent forms of S. pneumoniae could be “transformed” to virulent forms by combining heat-treated virulent bacteria with nonvirulent bacteria. The reverse was true and led to the conclusion that the virulence traits were heritable and capable of surviving mild heat treatment. Subsequently Avery et al. (1944) conducted experiments in which the “transforming principle” had characteristics of DNA, and the transforming factors did not test positive for proteins or RNA. Avery et al. (1944) showed that enzymes that degrade proteins or RNA did not degrade the “transforming principle” but that enzymes that could degrade DNA did. Hershey and Chas...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• About the Author
• Preface to the Fourth Edition
• Preface to the Third Edition
• Preface to the Second Edition
• Preface to the First Edition
• Acknowledgments
• Part I: Genes and Genome Organization in Eukaryotes
• Part II: Molecular Genetic Techniques
• Part III: Applications in Entomology
• Glossary
• Index