Biological Sciences
DNA replication
DNA replication is the process by which a cell makes an identical copy of its DNA. It occurs during the S phase of the cell cycle and involves the unwinding of the DNA double helix, followed by the synthesis of new complementary strands using the existing strands as templates. This process ensures that genetic information is faithfully passed on to daughter cells during cell division.
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8 Key excerpts on "DNA replication"
eBook - PDF- Alasdair Steven, Wolfgang Baumeister, Louise N. Johnson, Richard N. Perham(Authors)
- 2016(Publication Date)
- Garland Science(Publisher)
The final result is a complete and accurate copy of the original double-stranded DNA. DNA is copied by DNA polymerases The first enzyme capable of replicating DNA ( DNA polymerase ) was discovered by Arthur Kornberg and colleagues in E. coli, and is now known as DNA polymerase I ( Pol I). Because mutations in the gene encoding this enzyme were later found not to be lethal, it turned out that Pol I is not the enzyme that copies DNA as the helicase unwinds it. Further experiments identified this as Pol III. Instead, Pol I has a key role in another part of the replication pro-cess and, as described in Chapter 4, in some areas of DNA repair. DNA polymerases are now seen as a diverse set of enzymes that fall into seven distinct superfamilies (A, B, C, D, X, Y, and the reverse transcriptases), based on sequence analysis. Polymerases in these superfam-ilies can also be classified, based on whether they primarily function in DNA replication or repair. Replicative DNA polymerases are found in family A (mitochondria, bacteriophage T7), family B (human DNA pols alpha, delta, and epsilon; viral DNA polymerases—herpes-virus, vaccinia virus, adenovirus; bacteriophage T4 and phi29 DNA polymerases), family C (bacterial DNA pols), or family D (archaeal DNA pols). The enzymes that act in DNA repair are in family A (DNA polymerase I), family X (human DNA pol beta), or family Y (transle-sion DNA pols that can replicate past DNA damage). DNA polymerases copy an ssDNA template using dNTPs as substrate. The newly formed DNA strand is synthesized in the direction 5 ′ –3 ′ , dNTPs being added one at a time in a sequence complementary to the base sequence on the strand (3 ′ –5 ′ ) being copied ( Figure 3.14A ). The side product, pyrophosphate, can be hydrolyzed by a suitable phosphatase to two molecules of P i ; thus the addition of one nucleotide to the growing strand utilizes the free energy of hydrolysis of two phosphoanhydride bonds.
eBook - PDF- Charlotte W. Pratt, Kathleen Cornely(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
A human cell contains 46 separate DNA molecules—chromosomes—comprising over 6 billion base pairs. Lined up end-to-end, these molecules would be slightly longer than 2 m, but the average diameter of a mammalian nucleus is only 6 μm (0.000006 m). Fitting all the DNA into the nucleus would be like stuffing a 100-km strand of hair into a backpack. Not surprisingly, cells have elaborate mechanisms for keeping DNA neatly packaged as well as unpacking it so that it can be copied. DNA replication can be considered to be part of the central dogma of molecular biology: the information in a parent DNA molecule must be copied to produce two identical DNA molecules that are passed on to daughter cells when the parent cell divides. In this chapter, we’ll look at the process of DNA replication in detail, as well as some of the challenges cells face in accurately replicating DNA, repairing damaged DNA, and storing it safely. DO YOU REMEMBER? • A DNA molecule contains two antiparallel strands that wind around each other to form a double helix in which A and T bases in opposite strands, and C and G bases in opposite strands, pair through hydrogen bonding (Section 3.1). • Double-stranded nucleic acids are denatured at high temperatures; at lower temperatures, com- plementary polynucleotides anneal (Section 3.1). • A DNA molecule can be sequenced or amplified by using DNA polymerase to make a copy of a template strand (Section 3.5). • A reaction that hydrolyzes a phosphoanhydride bond in ATP occurs with a large change in free energy (Section 12.3). C H A P T E R 2 0 DNA replication AND REPAIR When Watson and Crick described the complementary, double-stranded nature of DNA in 1953, they recognized that DNA could be duplicated by a process involving sep- aration of the strands followed by the assembly of two new complementary strands. This mechanism of copying, or replication, was elegantly demonstrated by Matthew Meselson and Franklin Stahl in 1958.
No longer available |Learn more- Gustavo Blanco, Antonio Blanco(Authors)
- 2017(Publication Date)
- Academic Press(Publisher)
Chapter 21The Genetic Information (I)
Abstract
DNA biosynthesis occurs when a cell divides, in a process called replication . It involves separation of the DNA double helix and subsequent synthesis of complementary DNA strand, using the parent DNA chain as a template. Helicase unwinds the DNA strands and topoisomerase relieves tensions originated by the unwinding process. “Replication forks” move in opposite directions to form the new DNA. First, an RNA primer of 10 nucleotides in length is formed by α-primase. DNA elongation is catalyzed by polymerases , which assemble the new strand of DNA by addition of complementary nucleotides on each strand of the original DNA. As the chains are synthesized in the 5′ to 3′ direction, it can be performed continuously on one strand (leading strand) . The other strand (lagging strand ) has to be synthesized in segments (Okasaki fragments ). Structural units used for synthesis enter as deoxyribonucleoside triphosphates (dATP, dGTP, dTTP, and dCTP). Telomerase adds repeated sequences to the end of chromosome to replenish the segments lost after each replication. DNA repair mechanisms correct errors during the process of DNA synthesis. DNA recombination is an event that takes place in the gametes during meiosis. It involves the exchange of DNA segments between two homologous chromosomes. Restriction endonucleases are enzymes which digest phosphodiester bonds at specific sites (palindromic sites) in the DNA double helix. RNA biosynthesis is performed via a process called transcription . It involves the assembly of a complementary RNA using DNA as a template. It is catalyzed by RNA polymerases . Only one of the DNA strands serves as a template. Ribonucleoside triphosphate molecules (ATP, GTP, CTP, and UTP) are used for RNA synthesis. mRNA synthesis starts by binding to a promoter. Transcription factors are responsible for enzyme-promoter interaction. RNA synthesis proceeds in the 5′ to 3′ direction. The 5′ end of the newly synthesized RNA strand receives a “cap” of triphosphate 7-methyl-guanosine, which provides stability. One hundred to two hundred adenine nucleotides are added at the 3′ end (poly A tail ). Reverse transcriptase
eBook - PDF- Charlotte W. Pratt, Kathleen Cornely(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
519 CHAPTER 20 A human cell contains 46 separate DNA molecules—chromosomes—comprising over 6 billion base pairs. Lined up end-to-end, these molecules would be slightly longer than 2 m, but the average diameter of a mammalian nucleus is only 6 μm (0.000006 m). Fitting all the DNA into the nucleus would be like stuffing a 100-km strand of hair into a backpack. Not surprisingly, cells have elaborate mechanisms for keeping DNA neatly packaged as well as unpacking it so that it can be copied. DNA replication can be considered to be part of the central dogma of molecular biology: the information in a parent DNA molecule must be copied to produce two identical DNA molecules that are passed on to daughter cells when the parent cell divides. In this chapter, we’ll look at the process of DNA replication in detail, as well as some of the challenges cells face in accurately replicating DNA, repairing damaged DNA, and storing it safely. 20.1 The DNA replication Machinery When Watson and Crick described the complementary, double-stranded nature of DNA in 1953, they recognized that DNA could be duplicated by a process involving separation of the strands followed by the assembly of two new complementary strands. This mechanism of copying, or replication, was elegantly demonstrated by Matthew Meselson and Franklin DO YOU REMEMBER? • A DNA molecule contains two antiparallel strands that wind around each other to form a double helix in which A and T bases in opposite strands, and C and G bases in opposite strands, pair through hydrogen bonding (Section 3.1). • Double-stranded nucleic acids are denatured at high temperatures; at lower temperatures, com- plementary polynucleotides anneal (Section 3.1). • A DNA molecule can be sequenced or amplified by using DNA polymerase to make a copy of a template strand (Section 3.5). • A reaction that hydrolyzes a phosphoanhydride bond in ATP occurs with a large change in free energy (Section 12.3).
eBook - PDF- Donald Voet, Judith G. Voet(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
The surprising intri- cacy of DNA replication compared to the chemically similar transcription process (Section 26-2) arises from the need for extreme accuracy in DNA replication so as to preserve the integrity of the genome from generation to generation. A. Replication Forks DNA is replicated by enzymes known as DNA-directed DNA polymerases or simply DNA polymerases. These enzymes utilize single-stranded DNA as templates on which to catalyze the synthesis of the complementary strand from the appropriate deoxynucleoside triphosphates (Fig. 25-1). The incoming nucleotides are selected by their ability to form Watson–Crick base pairs with the template DNA so that the newly synthesized DNA strand forms a dou- ble helix with the template strand. Nearly all known DNA polymerases can only add a nucleotide donated by a nucle- oside triphosphate to the free 3′-OH group of a base paired polynucleotide so that DNA chains are extended only in the 5′ → 3′ direction. DNA polymerases are discussed further in Sections 25-2A, 25-2B, and 25-4B. 1 DNA replication: An Overview A. Replication Forks B. Role of DNA Gyrase C. Semidiscontinuous Replication D. RNA Primers 2 Enzymes of Replication A. DNA Polymerase I B. DNA Polymerase III C. Unwinding DNA: Helicases and Single-Strand Binding Protein D. DNA Ligase E. Primase 3 Prokaryotic Replication A. Bacteriophage M13 B. Bacteriophage X174 C. Escherichia coli D. Fidelity of Replication 4 Eukaryotic Replication A. The Cell Cycle B. Eukaryotic Replication Mechanisms C. Reverse Transcriptase D. Telomeres and Telomerase 5 Repair of DNA A. Direct Reversal of Damage B. Excision Repair C. Mismatch Repair D. The SOS Response E. Double-Strand Break Repair F. Identification of Carcinogens 6 Recombination and Mobile Genetic Elements A. Homologous Recombination B. Transposition and Site-Specific Recombination 7 DNA Methylation and Trinucleotide Repeat Expansions 1150 Chapter 25 DNA replication, Repair, and Recombination a.
eBook - PDF- Charlotte W. Pratt, Kathleen Cornely(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
582 DNA replication and Repair CHAPTER 20 DO YOU REMEMBER? • A DNA molecule contains two antiparallel strands that wind around each other to form a double helix in which A and T bases in opposite strands, and C and G bases in opposite strands, pair through hydrogen bonding (Section 3.1). • Double-stranded nucleic acids are denatured at high temperatures; at lower temperatures, com- plementary polynucleotides anneal (Section 3.2). • Changes in a DNA sequence can cause disease (Section 3.3). • A reaction that hydrolyzes a phosphoanhydride bond in ATP occurs with a large change in free energy (Section 12.3). A human cell contains 46 separate DNA molecules—chromosomes—comprising over 6 billion base pairs. Lined up end-to-end, these molecules would be slightly longer than 2 m, but the average diameter of a mammalian nucleus is only 6 μm (0.000006 m). Fitting all the DNA into the nucleus would be like stuffing a 50-mile-long strand of hair into a backpack. Not surprisingly, cells have elaborate mechanisms for keeping DNA neatly packaged as well as unpacking it so that it can be copied. DNA replication can be considered to be part of the cen- tral dogma of molecular biology: the information in a parent DNA molecule must be copied to produce two identical DNA molecules that are passed on to daughter cells when the parent cell divides. In this chapter, we will look at the process of DNA replication in detail, as well as some of the challenges cells face in accurately replicating DNA, repairing damaged DNA, and storing it safely. The Tools and Techniques section at the end of the chapter describes some of the methods used to manipulate and sequence DNA. 20.1 The DNA replication Machinery LEARNING OBJECTIVES Summarize the actions of the enzymes and other proteins involved in synthesizing the leading and lagging strands. • Explain why DNA replication is semiconservative. • Relate the structure of helicase to its function. • Explain why DNA replication requires an RNA primer.
eBook - PDF- Shirley Lehnert(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
The genetic information stored in the DNA contains the instructions for all the proteins the organism will ever synthesize. DNA replication takes place at a Y-shaped structure called a replication fork. A self-correcting DNA polymerase enzyme catalyzes nucleotide poly-merization in a 5 0 -to-3 0 direction, copying a DNA template strand with a high degree of fidelity. Since the two strands of a DNA double helix are antiparallel, this 5 0 -to-3 0 DNA synthesis can take place continuously on only one of the strands (the leading strand). On the lagging strand, short DNA fragments synthesized in the 5 0 -to-3 0 direction are ligated together. In addition to DNA polymerase, DNA replication requires the cooperation of many proteins associated with each other at a replication fork to form ‘‘replication machines.’’ Before the synthesis of a particular protein can begin, the corresponding mRNA molecule is produced by transcription. mRNA is synthesized by RNA polymerase II, one of three RNA polymerases found in eukaryotic cells. This enzyme requires a series of additional proteins, termed the 48 Biomolecular Action of Ionizing Radiation general transcription factors, to initiate transcription on a purified DNA tem-plate and still more proteins (including chromatin-remodeling complexes and histone acetyltransferases) to initiate transcription on its chromatin template inside the cell. During the elongation phase of transcription, the nascent RNA undergoes three types of processing events: a special nucleotide is added to its 5 0 end (capping), intron sequences are removed from the middle of the RNA molecule (splicing), and the 3 0 end of the RNA is generated (cleavage and polyadenylation). Genes for which RNA is the end product are usually tran-scribed by either RNA polymerase I or III. RNA polymerase I synthesizes ribosomal RNAs as large precursors that are chemically modified, cleaved, and assembled into ribosomes in the nucleolus.
eBook - PDF- Rene Fester Kratz, Lisa Spock(Authors)
- 2023(Publication Date)
- For Dummies(Publisher)
FIGURE 7-3: The results of Taylor, Woods, and Hughes experiment show that DNA replication is semiconservative. 110 PART 2 DNA: The Genetic Material Most eukaryotic DNA is linear, whereas most bacterial DNA (and your mitochon- drial DNA) is circular. The shape of the chromosome (an endless loop versus a string) doesn’t affect the process of replication at all. However, the shape means that circular DNAs have special problems to solve when replicating their hoop- shaped chromosomes. See the section “How Circular DNAs Replicate” later in this chapter to find out more. Meeting the replication crew For successful replication, several players must be present: » Template DNA, a double-stranded molecule that provides a pattern to copy » Nucleotides, the building blocks necessary to make new DNA » Enzymes and various proteins that do the unzipping and assembly work of DNA replication, which is also called DNA synthesis Template DNA In addition to the material earlier in this chapter detailing how the template DNA is replicated in a semiconservative manner (see the section “Unzipped: Creating the Pattern for More DNA”), it’s vitally important for you to understand all the meanings of the term template. » Every organism’s DNA exists in the form of chromosomes. During DNA replication, cells use the chromosomes being copied as the pattern for making new chromosomes. » Both strands of each double-stranded original molecule are copied, and therefore, each of the two strands serves as a template (that is, a pattern) for replication. The bases of the template DNA provide critical information needed for replication. Each new base of the newly replicated strand must be complementary to the base opposite it on the template strand (see Chapter 5 for more about the complemen- tary nature of DNA). For example, if an A is present in the template strand, then a T must be added opposite in the newly replicated strand.
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