Replication DNA synthesis

Phenol was reported to induce DNA oxidative damage in human promyelocytic HL60 cells and to inhibit repair of radiation-induced chromosomal breaks in human leukocytes (Morimoto et al., 1976). However, it only slightly inhibited DNA repair synthesis and DNA replication synthesis in WI-38 human diploid fibroblasts (Poirier et al., 1975). 

Figure 37.2 A simplified schematic view of cell cycle progression in diatoms, with critical arrest points and dominant processes indicated. Most diatoms arrest at the Gl/S boundary, but a secondary arrest point can occur during the G2/M phase. M mitosis S DNA replication (synthesis) G1 and G2 gap phases.

Nucleus The nucleus is the "Control Center" of the cell, which contains DNA (genetic information) in the form of genes, and also information for the formation of proteins. Information is carried on chromosomes, which are a form of DNA. Site for DNA replication, synthesis and processing of messenger RNA s. 

Telomere replication, (a) In replication of the lagging strand, short RNA primers are added (pink) and extended hy DNA polymerase. When the RNA primer at the 5 end of each strand is removed, there is no nucleotide sequence to read in the next round of DNA replication. The result is a gap (primer gap) at the 5 end of each strand (only one end of a chromosome is shown in this figure), (h) Asterisks indicate sequences at the 3 end that cannot he copied hy conventional DNA replication. Synthesis of telomeric DNA hy telomerase extends the 5 ends of DNA strands, allowing the strands to he copied hy normal DNA replication. 

A decrease in the activity of primase would account for the low rate of DNA replication. Synthesis of DNA itself requires the prior synthesis of RNA primers. Also, decreased rates of dNTP synthesis could slow replication. 

Millner GC, Shaddock JG, Harbison RD, et al. 1988. A comparison between the in vitro DNA repair assay and the in vivo/in vitro DNA repair and DNA replicative synthesis assays for detecting hepatocarcinogens [Abstract]. Environ Mol Mutagen 11 70. 

Fig. 2.10 The polymerase chain reaction (PCR). Vertical arrows indicate the heat-induced dissociation of the double strands and the association with the primers. Horizontal arrows symbolize the DNA replication (synthesis) step. With each cycle, the number of DNA strands containing the sequence of interest is doubled. See Box 3 for more details.

Once the broad outlines of DNA replication and protein biosynthesis were established scien tists speculated about how these outlines af fected various origins of life scenarios A key question concerned the fact that proteins are re quired for the synthesis of DNA yet the synthesis of these proteins is coded for by DNA Which came first DNA or proteins How could DNA store genetic infor mation if there were no enzymes to catalyze the polymerization of its nucleotide components How could there be proteins if there were no DNA to code for them ... 

Chromosomal organization, DNA replication, transcription, ribosome synthesis, and mitosis in plant cells are grossly similar to the analogous features in animals. 

The consequence of ADA deficiency is accumulation of adenosine and 2 -deoxyadenosine, substances toxic to lymphocytes, important cells in the immune response. 2 -Deoxyadenosine is particularly toxic because its presence leads to accumulation of its nucleotide form, dATP, an essential substrate in DNA synthesis. Elevated levels of dATP actually block DNA replication and cell division by inhibiting synthesis of the other deoxynncleoside 5 -triphosphates (see Chapter 27). Accumulation of dATP also leads to selective depletion of cellular ATP, robbing cells of energy. Children with ADA SCID fail to develop normal immune responses and are susceptible to fatal infections, unless kept in protective isolation. 

Nucleic acids are the last of the four major classes of biomolecules we ll consider. So much has been written and spoken about DNA in the media that the basics of DNA replication and transcription are probably known to you. Thus, we ll move fairly quickly through the fundamentals and then focus more closely on the chemical details of DNA sequencing and synthesis. 

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The eukaryotic somatic cell cycle is defined by a sequential order of tasks a dividing cell has to complete it must replicate its DNA, segregate its chromosomes, grow, and divide. The cell cycle can be divided into four discrete phases. DNA replication is restricted to S phase (DNA synthesis phase), which is preceded by a gap phase called G1 and followed by a gap phase called G2. During mitosis (M phase) the sister chromatids are segregated into two new daughter nuclei and mitosis is completed by the division of the cytoplasm termed cytokinesis (Fig. 1). 

DNA synthesis during S phase of the cell cycle resulting in a doubling of the genomic DNA. Replication can be subdivided into three distinct phases initiation, elongation, and termination. 

Figure 35-5. DNA replication is semiconservative. During a round of replication, each of the two strands of DNA is used as a template for synthesis of a new, complementary strand.

Section IV describes the structures and functions of the nucleotides and nucleic acids, and covers many major topics such as DNA replication and repair, RNA synthesis and modification, and protein synthesis. It also discusses new findings on how genes are regulated and presents the principles of recombinant DNA technology. 

Abstract. In eukaryotic cells, replicated DNA molecules remain physically connected from their synthesis in S phase until they are separated during anaphase. This phenomenon, called sister chromatid cohesion, is essential for the temporal separation of DNA replication and mitosis and for the equal separation of the duplicated genome. Recent work has identified a number of chromosomal proteins required for cohesion. In this review we discuss how these proteins may connect sister chromatids and how they are removed from chromosomes to allow sister chromatid separation at the onset of anaphase. 

This presented a more difficult problem How do the double-helical strands separate during DNA synthesis In a rapidly growing cell such as E. coli it has been calculated that if the strands separate by untwisting, the molecule would have to rotate at 10,000 rpm, a rate that is highly improbable. The answer to this problem lies in an understanding of the mechanism of DNA replication at the enzyme level. We will return to this subject after first considering the enzymes involved in DNA synthesis. 

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