Hartl, Jones - Genetics. Principlers and analysis - 1998 (522927), страница 58
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White, M. Skolnick, and R. W. Davis. 1980. Construction of a genetic linkage map in manusing restriction fragment length polymorphisms. American Journal of Human Genetics 32: 314.Carlson, E. A. 1987. The Gene: A Critical History. 2d ed. Philadelphia: Saunders.Creighton, H. S., and B. McClintock. 1931. A correlation of cytological and genetical crossing over in Zea mays.Proceedings of the National Academy of Sciences, USA 17: 492.Fincham, J.
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Advances in Human Genetics 17: 99.Sturtevant, A. H. 1965. A History of Genetics. New York: Harper & Row.Sturtevant, A. H., and G. W. Beadle. 1962. An Introduction to Genetics. New York: Dover.Voeller, B. R., ed. 1968. The Chromosome Theory of Inheritance: Classical Papers in Development and Heredity.New York: Appleton-Century-Crofts.White, R., and J.-M. Lalouel. 1988. Chromosome mapping with DNA markers. Scientific American, February.Page 172Human chromosomes isolated from cells of an ovarian cancer. Each chromosome islabeled with a different color. Note the many abnormal chromosomes, containingtwo or more colors,that have been formed by breakage of other chromosomes andReunion of their broken parts in abnormal combinations. Note also that thiscell has 63 chromosomes (instead of the normal 46) and that one of theX chromosomes is missing.[Courtesy of David C.
Ward and Michael R. Speicher.]Page 173Chapter 5—The Molecular Structure and Replication of the Genetic MaterialCHAPTER OUTLINE5-1 The Chemical Composition of DNA5-2 The Physical Structure of the Double Helix5-3 What a Genetic Material Needs That DNA Supplies5-4 The Replication of DNAThe Basic Rule for the Replication of Nucleic AcidsThe Geometry of DNA Replication5-5 DNA Synthesis5-6 Discontinuous ReplicationFragments in the Replication ForkInitiation by an RNA PrimerThe Joining of Precursor FragmentsOther Proteins Needed for DNA Replication5-7 The Isolation and Characterization of Particular DNA FragmentsDenaturation and RenaturationNucleic Acid HybridizationRestriction Enzymes and Site-Specific DNA CleavageGel ElectrophoresisThe Southern Blot5-8 The Polymerase Chain Reaction5-9 Determination of the Sequence of Bases in DNAThe Sequencing ProcedureClinical Use of Dideoxynucleoside AnalogsChapter SummaryKey TermsReview the BasicsGuide to Problem SolvingAnalysis and ApplicationsChallenge ProblemsFurther ReadingGeNETics on the webPRINCIPLES• A DNA strand is a polymer of A, T, G and C deoxyribonucleotides joined 3' to 5' by phosphodiester bonds.• The two DNA strands in a duplex are held together by hydrogen bonding between the A–T and G-C base pairs.• DNA replication is semiconservative and takes place only in the 5' to 3' direction; successive nucleotides areadded only at the 3' end.• Each type of restriction endonuclease enzyme cleaves double-stranded DNA at a particular sequence of basesusually four or six nucleotides in length.• Separated strands of DNA or RNA that are complementary in nucleotide sequence can come together (hybridize)spontaneously to form duplexes.• In the polymerase chain reaction, short oligonucleotide primers are used in successive cycles of DNA replicationto amplify selectively a particular region of a DNA duplex.• The DNA fragments produced by a restriction enzyme can be separated by electrophoresis, isolated, sequenced,and manipulated in other ways.CONNECTIONSCONNECTION: The Double HelixJames D.
Watson and Francis H. C. Crick 1953A structure for deoxyribose nucleic acidCONNECTION: Replication by HalvesMatthew Meselson and Franklin W. Stahl 1958The replication of DNA in Escherichia coliPage 174Analysis of the patterns of inheritance and even the phenotypic expression of genes reveals nothing about genestructure at the molecular level, how genes are copied to yield exact replicas of themselves, or how they determinecellular characteristics.
Understanding these basic features of heredity requires identification of the chemical natureof the genetic material and the processes through which it is replicated. In Chapter 1, we reviewed the experimentalevidence demonstrating that the genetic material is DNA. The structure of DNA was described as a helix of twopaired, complementary strands, each composed of an ordered string of nucleotides bearing A (adenine), T(thymine), G (guanine), or cytosine (C).
Watson-Crick base pairing between A and T and between G and C in thecomplementary strands holds the strands together. The complementarity also holds the key to replication, becauseeach strand can serve as a template for the synthesis of a new complementary strand. In this chapter, we take acloser look at DNA structure and its replication.
We also consider how our knowledge of DNA structure andreplication has been used in the development of laboratory techniques for isolating fragments that contain genes orparts of genes of particular interest and for determining the sequence of bases in DNA fragments.5.1—The Chemical Composition of DNADNA is a polymer—a large molecule that contains repeating units—composed of 2'-deoxyribose (a five-carbonsugar), phosphoric acid, and the four nitrogen-containing bases denoted A, T, G, and C. The chemical structures ofthe bases are shown in Figure 5.1.
Note that two of the bases have a double-ring structure; these are called purines.The other two bases have a single-ring structure; these are called pyrimidines.• The purine bases are adenine (A) and guanine (G).• The pyrimidine bases are thymine (T) and cytosine (C).In DNA, each base is chemically linked to one molecule of the sugar deoxyribose, forming a compound called anucleoside.
When a phosphate group is also attached to the sugar, the nucleoside becomes a nucleotide (Figure5.2). Thus a nucleotide is a nucleoside plus a phosphate. In the conventional numbering of the carbon atoms in thesugar in Figure 5.2, the carbon atom to which the base is attached is the 1' carbon. (The atoms in the sugar aregivenFigure 5.1Chemical structures of adenine, thymine, guanine, and cytosine, the four nitrogen-containing bases in DNA.In each base, the nitrogen atom linked to the deoxyribose sugar is indicated. The atoms shownin red participate in hydrogen bonding between the DNA base pairs, as explained in Section 5.2.Page 175Figure 5.2A typical nucleotide showing the three major components (phosphate, sugar, and base), thedifference between DNA and RNA, and the distinction between a nucleoside (no phosphate group) and anucleotide (with phosphate).
Nucleotides may contain one phosphate unit (monophosphate), twosuch units (diphosphate) or three (triphosphate).primed numbers to distinguish them from atoms in the bases.) The nomenclature of the nucleoside and nucleotidederivatives of the DNA bases is somewhat complicated and is summarized in Table 5.1. Most of these terms arenot needed in this book; they are included because they are likely to be encountered in further reading.In nucleic acids, such as DNA and RNA, the nucleotides are joined to form a polynucleotide chain, in which thephosphate attached to the 5' carbon of one sugar is linked to the hydroxyl group attached to the 3' carbon of thenext sugar in line (Figure 5.3). The chemical bonds by which the sugar components of adjacent nucleotides arelinked through the phosphate groups are called phosphodiester bonds.
The 5'-3'-5'-3' orientation of these linkagescontinues throughout the chain, which typically consists of millions of nucleotides. Note that the terminal groups ofeach polynucleotide chain are a 5'-phosphate (5'-P) group at one end and a 3'-hydroxyl (3'-OH) group at the other.The asymmetry of the ends of a DNA strand implies that each strand has a polarity determined by which end bearsthe 5'-phosphate and which end bears the 3'-hydroxyl.Three years before Watson and Crick proposed their essentially correct three-dimensional structure of DNA as adouble helix, Erwin Chargaff developed a chemical technique to measure the amount of each base present in DNA.As we describe his technique, we will let the molar concentration of any base be represented by the symbol for thebase in square brackets; for example, [A] denotes the molar concentration of adenine.
Chargaff used his techniqueto measure the [A], [T], [G], and [C] content of the DNA from a variety of sources. He found that the basecomposition of the DNA, d efined as the percent G + C, differs among species but isTable 5.1 DNA nomenclatureBaseNucleosideNucleotideAdenine (A)DeoxyadenosineDeoxyadenosine-5'monophosphate (dAMP)diphosphate (dADP)triphosphate (dATP)Guanine (G)DeoxyguanosineDeoxyguanosine-5'monophosphate (dGMP)diphosphate (dGDP)triphosphate (dGTP)Thymine (T)DeoxythymidineDeoxythymidine-5'monophosphate (dTMP)diphosphate (dTDP)triphosphate (dTTP)Cytosine (C)DeoxycytidineDeoxycytidine-5'monophosphate (dCMP)diphosphate (dCDP)triphosphate (dCTP)Page 176Figure 5.3Three nucleotides at the 5' end of a single polynucleotide strand.
(A) The chemical structure of thesugar-phosphate linkages, showing the 5'-to-3' orientation of the strand (the red numbers are thoseassigned to the carbon atoms). (B) A common schematic way to depict a polynucleotide strand.constant in all cells of an organism and within a species. Data on the base composition of DNA from a variety oforganisms are given in Table 5.2.Chargaff also observed certain regular relationships among the molar concentrations of the different bases.
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