Molecular Biology And Genetics PdfBy Udolfo A. In and pdf 05.12.2020 at 13:52 8 min read
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Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Molecular Biology has emerged from the synthesis of two complementary approaches to the study of life—biochemistry and genetics—to become one of the most exciting and vibrant scientific fields at the end of the twentieth century.
This introductory chapter provides a brief history of the intellectual foundations of modern molecular biology and defines key terms and concepts that recur throughout the subsequent chapters. The concepts of molecular biology have become household words. DNA, RNA, and enzymes are routinely discussed in newspaper stories, prime-time television shows, and business weeklies.
The passage into popular culture is complete only 40 years after the discovery of the structure of deoxyribonucleic acid DNA by James Watson and Francis Crick and only 20 years after the first steps toward genetic engineering. With breathtaking speed, these basic scientific discoveries have led to astonishing scientific and practical implications: the fundamental biochemical processes of life have been laid bare.
The evolutionary record of life can be read from DNA sequences. Genes for proteins such as human insulin can be inserted into bacteria, which then can inexpensively produce large and pure amounts of the protein. Farm animals and crops can be engineered to produce healthier and more. Sensitive and reliable diagnostics can be developed for viral diseases such as AIDS, and treatments can be developed for some hereditary diseases, such as cystic fibrosis.
Molecular biology is certain to continue its exciting growth well into the next century. As its frontiers expand, the character of the field is changing. With ever growing databases of DNA and protein sequences and increasingly powerful techniques for investigating structure and function, molecular biology is becoming not just an experimental science, but a theoretical science as well. The role of theory in molecular biology is not likely to resemble the role of theory in physics, in which mathematicians can offer grand unifying theories.
In biology, key insights emerge less often from first principles than from interpreting the crazy quilt of solutions that evolution has devised. Interpretation depends on having theoretical tools and frameworks.
Sometimes, these constructs are nonmathematical. Increasingly, however, the mathematical sciences—mathematics, statistics, and computational science—are playing an important role. This book emerged from the recognition of the need to cultivate the interface between molecular biology and the mathematical sciences.
In the following chapters, various mathematicians working in molecular biology provide glimpses of that interface. The essays are not intended to be comprehensive up-to-date reviews, but rather vignettes that describe just enough to tempt the reader to learn more about fertile areas for research in molecular biology. This introductory chapter briefly outlines the intellectual foundations of molecular biology, introduces some key terms and concepts that recur throughout the book, and previews the chapters to follow.
Historically, molecular biology grew out of two complementary experimental approaches to studying biological function: biochemistry and genetics Figure 1. Biochemistry involves fractionating breaking up the molecules in a living organism, with the goal of purifying and characterizing the chemical components responsible for carrying out a particular function.
To do this, a biochemist devises an assay for. In vitro literally, in glass assays were accomplished back in the days when biologists were still grappling with the notion of vitalism. Originally, it was thought that life and biochemical reactions did not obey the known laws of chemistry and physics.
Living organisms are composed principally of carbon, hydrogen, oxygen, and nitrogen; they also contain small amounts of other key elements such as sodium, potassium, magnesium, sulfur, manganese, and selenium. These elements are combined in a vast array of complex macromolecules that can be classified into a number of major types: proteins, nucleic acids, lipids fats , and carbohydrates starches and sugars.
Of all the macromolecules, the proteins have the most diverse range of functions. The human body makes about , distinct proteins, including:.
In short, proteins do the work of the cell. From a structural standpoint, a protein is an ordered linear chain made of building blocks known as amino acids Figures 1. There are 20 distinct amino acids, each with its own chemical properties including size, charge, polarity, and hydrophobicity, or the tendency to avoid packing with water. Each protein is defined by its unique sequence of amino acids; there are typically 50 to amino acids in a protein.
The diagram shows a highly stylized view of this linear structure. Reprinted, by permission, from Richardson and Richardson The amino acid sequence of a protein causes it to fold into the particular three-dimensional shape, having the lowest energy. This gives the protein its specific biochemical properties, that is, its function.
Typically, the shape of a protein is quite robust. If the protein is heated, it will be denatured that is, lose its three-dimensional structure , but it will often reassume that structure refold when cooled. Predicting the folded structure of a protein from the amino acid sequence remains an extremely challenging problem in mathematical optimization.
The challenge is created by the combinatorial explosion of plausible shapes, each of which represems a local minimum of a complicated nonconvex function of which the global minimum is sought.
The second major approach to studying biological function has been genetics. Whereas biochemists try to study one single component purified away from the organism, geneticists study mutant organisms that are intact except for a single component. Genetics can be traced back to the pioneering experiments of Gregor Mendel in These key experiments elegantly illustrate the role of theory and abstraction in biology.
For his experiments, Mendel started with pure breeding strains of peas—that is, ones for which all offspring, generation after generation, consistently show a trait of interest. This Choice was key to interpreting the data. One of the traits that he studied was whether the pea made round or wrinkled seeds. Starting with pure breeding round and wrinkled strains, Mendel made a controlled cross to produce an F 1 generation.
The i th generation of the cross is denoted F i. Mendel noted that all of the F 1 generation consisted of round peas; the wrinkled trait had completely vanished. However, when Mendel crossed these F 1 peas back to the pure breeding wrinkled parent, the wrinkled trait reappeared: of the second generation, approximately half were round and half were wrinkled.
Moreover, when Mendel crossed the F 1 peas to themselves, he found that. On the basis of these and other experiments, Mendel hypothesized that traits such as roundness are affected by discrete factors—which today we call genes. In particular, Mendel suggested the following:. Each organism inherits two copies of a gene, one from each parent. Each parent passes on one of the two copies, chosen at random, to each offspring. Genes can occur in alternative forms, called alleles.
For example, the gene affecting seed shape occurs in one form allele A causing roundness and one form allele a causing wrinkledness. The pure breeding round and wrinkled plants carried two copies of the same allele, AA and aa , respectively. Individuals carrying two copies of the same gene are called homozygotes.
The F 1 generation consists of individuals with genotype Aa , with the round trait dominant over the wrinkled trait. Such individuals are called heterozygotes. In the cross of the F 1 generation Aa to the pure breeding wrinkled strain aa , the offspring were a mixture of Aa:aa according to which allele was inherited from the F 1 parent. In the cross between two F 1 parents Aa , the offspring were a mixture of AA:Aa:aa according to the binomial selection of alleles from the two parents.
It is striking to realize that the existence of genes was deduced in this abstract mathematical way. Probability and statistics were an intrinsic part of early genetics, and they have remained so.
Of course, Mendel did not have formal statistical analysis at his disposal, but he managed to grasp the key concepts intuitively. Incidentally, the famous geneticist and statistician R. Mendel probably discarded some outliers as likely experimental errors. It was almost 35 years before biologists had an inkling of where these hypothetical genes resided in the cell in the chromosomes and almost years before they understood their biochemical nature.
As suggested in Figure 1. Much like the great unifications in mathematics, molecular biology emerged from the recognition that the two apparently unrelated fields were, in fact, complementary perspectives on the same subject.
The first clues emerged from the study of mutant microorganisms in which gene defects rendered them unable to synthesize certain key macromolecules. Biochemical study of these genetic mutants showed that each lacked a specific enzyme. The answer depended on finding the biochemical nature of the gene itself, thereby uniting the fields. To purify the gene as a biochemical entity, one needed a test tube assay for heredity—something that might seem impossible. Fortunately, scientific serendipity provided a solution.
In a famous series of bacteriological studies, Griffith showed 50 years ago that certain properties such as pathogenicity could be transferred from dead bacteria to live bacteria. Avery et al. The surprising conclusion was that the gene appeared to be made of DNA. The notion of DNA as the material of heredity came as a surprise to most biochemists.
DNA was known to be a linear polymer of four building blocks called nucleotides referred to as adenine, thymine, cytosine, and guanine, and abbreviated as A, T, C, and G joined by a sugar-phosphate backbone. However, most knowledgeable scientists reckoned that the polymer was a boring, repetitive structural molecule that functioned as some sort of scaffold for more important components.
In the days before computers, it was not apparent how a linear polymer might encode information. In their legendary work in , Watson and Crick correctly inferred the structure of most DNA and, in so doing, explained the main secret of heredity. While some viruses have single-stranded DNA, the DNA of humans and of most other forms of life consists of two antiparallel chains strands in the form of a double helix in which the bases nucleotides pair up to form base pairs in a certain way Figure 1.
The sequences are complementary. The fact that the information is redundant explains the basis for the replication of living organisms: the two strands of the double helix unwind, and each serves as a template for the synthesis of a complete double helix that is passed on to a daughter cell. This process of replication is carded out by enzymes called DNA polymerases. Mutations are changes in the nucleotide sequence in DNA. Mutations can be induced by external.
Biochemical studies over the next decade showed that genes correspond to specific stretches of DNA along a chromosome much like individual files on a hard disk. These stretches of DNA can be expressed at particular times or under particular circumstances. Typically, gene expression begins with transcription of the DNA sequence into a messenger molecule made of ribonucleic acid RNA Figure 1.
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Molecular Biology: Academic Cell Update provides an introduction to the fundamental concepts of molecular biology and its applications. It deliberately covers a broad range of topics to show that molecular biology is applicable to human medicine and health, as well as veterinary medicine, evolution, agriculture, and other areas. The present Update includes journal specific images and test bank. It also offers vocabulary flashcards. The book begins by defining some basic concepts in genetics such as biochemical pathways, phenotypes and genotypes, chromosomes, and alleles. It also describes genetic processes such as transcription, recombination and repair, regulation, and mutations.
Such an approach is particularly efficient as the subject of molecular genetics now is far too advanced, large, and complex for much value to come from attempting.
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William Astbury described molecular biology in in Nature , as:. It is concerned particularly with the forms of biological molecules and [ It must at the same time inquire into genesis and function. Some clinical research and medical therapies arising from molecular biology are covered under gene therapy whereas the use of molecular biology or molecular cell biology in medicine is now referred to as molecular medicine. Molecular biology also plays important role in understanding formations, actions, and regulations of various parts of cells which can be used to efficiently target new drugs , diagnose disease, and understand the physiology of the cell.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Molecular Biology has emerged from the synthesis of two complementary approaches to the study of life—biochemistry and genetics—to become one of the most exciting and vibrant scientific fields at the end of the twentieth century. This introductory chapter provides a brief history of the intellectual foundations of modern molecular biology and defines key terms and concepts that recur throughout the subsequent chapters.
The journal, published since , is the official publication of the Spanish Society of Cardiology and founder of the REC Publications journal family. Articles are published in both English an Spanish in its electronic edition. The Impact Factor measures the average number of citations received in a particular year by papers published in the journal during the two receding years.