Volume 1

Principles and practice of medical genetics / edited by Alan E.H. Emery, David L. Rimoin ; associate editor, Jeffrey A. Sofaer ; editorial assistant, Isobel Black ; foreword by Victor A. McKusick.

Date:
1990
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Principles and practice of medical genetics / edited by Alan E.H. Emery, David L. Rimoin ; associate editor, Jeffrey A. Sofaer ; editorial assistant, Isobel Black ; foreword by Victor A. McKusick. Source: Wellcome Collection.

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    2. Gene structure and function in eukaryotic organisms Gregory S. Barsh Charles J. Epstein INTRODUCTION Perhaps nothing has contributed more to our present state of knowledge regarding gene structure and function than the ability to efficiently manipulate pieces of DNA in vitro and to introduce the product back into a living cell. This revolution in molecular biology has led to an exponential increase in data regarding the physical structure of the human genome which may not plateau for several decades. Inundated with DNA sequences, it is sometimes possible to lose sight of the primary lesson of classical genetics - that a gene, rather than being a string of nucleotide pairs, is the determinant of an inherited phenotype which segregates from one generation to the next. As human geneticists, the challenge for the future is to explain biological phenomena with the physical language we already understand. conservative. Thus, any particular duplex contains a newly synthesized strand from the parental cell and an older previously existing strand. The first step in communication of genetic informa tion from the nucleus to the cytoplasm is the transcription of DNA into messenger RNA. During this process, the DNA duplex unwinds and one of the strands serves as the template for synthesis of a complementary RNA strand. RNA is distinguished from DNA by the presence of uracil instead of thymine, ribose instead of deoxyribose, and a different three-dimensional folding pattern. A hybrid DNA-RNA duplex is transiently formed during the transcriptional process, but completed messenger RNA remains single stranded and functions as the vehicle for translating nucleic acid into protein sequence. In prokaryotes a single enzyme, RNA polymerase, THE TOPOLOGY OF DNA STRUCTURE The complementary strands of the double helix underlie the molecular basis of DNA replication, transcription, and recombination The preservation, communication, and exchange of genetic information are fundamental biological processes intricately linked to the double-stranded structure of native DNA (Fig. 2.1). According to the rules of Watson and Crick base pairing, guanine pairs with cytosine and adenine pairs with thymine (or its analogue, uracil, in RNA). The hydrogen bonds formed between these pyrimidine-purine pairs (guanine and adenine are pur ines; cytosine, thymine, and uracil are pyrimidines) help to stabilize and ‘seal’ the two complementary strands together (Saenger 1984). Genetic information is preserved by DNA replication (Kornberg 1980). During this process, the two parental strands separate, and each serves as a template for the synthesis of a new complementary strand (Fig. 2.2). Each daughter cell inherits one strand of the parental duplex; this pattern of DNA replication is described as semi- ® I 1 phosphodiester linkage pyrimidines deoxyribose purines Fig. 2.1 The complementary structure of double-stranded DNA.