Chromosomes duplication

Recent studies have concentrated on control mechanisms, such as the crucial part played by cyclin dependent protein kinases in triggering chromosome duplication and segregation (Nurse 1990) and surveillance mechanisms (checkpoints) that monitor the fidelity of these two processes (Hartwell Weinert 1989). This focus on control is however a recent phenomenon. Earlier studies, largely... 

The anti-Pseudomonas action of norfloxacin is related to its ability to inhibit chromosome duplication in rapidly-dividing cells. Which of the following enzymes participates in bacterial DNA replication and is directly inhibited by this antibiotic ... 

Bowers JE, Chapman BA, Rong J, Paterson AH (2003) Unraveling angiosperm genome evolution by phylogenetic analysis of chromosomal duplication events. Nature 422 433 38... 

Onion cells in the process of dividing show chromosomes that consist of DNA and protein molecules clumped together. During division, the chromosomes duplicate themselves such that each new cell receives a Rill set of chromosomes identical to the set in the parent cell. 

During cellular mitosis, DNA and certain cellular proteins bundle together into chromosomes, which are visible under a microscope. These chromosomes duplicate themselves and then divide evenly into two separate cells called daughter cells. 

DNA contains the genetic information transmitted to each daughter cell when cells divide. The DNA usually exists in the form of nucleoprotein (DNA-protein) complexes called chromosomes. A prokaryotic cell contains a single chromosome. Prior to cell division this chromosome duplicates and segregates so that an identical complement of DNA goes to each of two newly formed daughter cells. 

The histones present in chromatin are of five major types HI, H2a, H2b, H3, and H4 (table 25.2). The lysine-rich histone HI is not present in the nucleosome core particles, as evidenced by its release on extensive nuclease treatment and the finding that HI is the only histone that readily exchanges between free and DNA-bound histone. HI may play a key role in the conversion of chromatin to the highly compacted chromosome that occurs immediately before cell division. The other eight histones, two each of the other four histones, form the protein core of the nucleosome. These protein octamers do not come apart even when chromosomes duplicate. 

The c-myc gene encodes a 49-kd protein that is highly concentrated in the nucleus of the cell. The concentration of c-myc protein normally varies appreciably with the metabolic state of the cell, increasing by more than an order of magnitude in cells just prior to chromosome duplication and cell division. 

G phase. That period of the cell cycle in which preparations are being made for chromosome duplication, which takes place in the S phase. 

The process of cell division is a nice example of many of these motors working together. Figure 3 illustrates this in a simple schematic. Here, from the parent cell (A), duplication of the centriole occurs (B), and the centrioles migrate to opposite ends of the cell (C). Chromosome duplication and condensation follow (D), the nuclear envelope breaks down, and the two sets of chromosomes are drawn to the centrioles at opposite ends of the cell (E). Cell cleavage then takes place (F and G), and two... 

Chromosome duplication in eukaryotic cells requires the enzyme telomerase which replicates the chromosome ends, the telomeres, a task that cannot be carried out by DNA replicases. (Telomerase is a ribonucleoprotein where the RNA moiety serves as template for addition of short nucleotides to the 3 end of the chromosome. The telomerase contains reverse transcriptase motifs which are essential for the duplication of the telomeres. For further information see ref. 20.). The cell-cycle clock is tightly coupled to the telomerase clock. ... 

E. coli can divide every 40 minutes. Thus, its DNA (MW = 2.2x 10 ) can be duplicated in 40 minutes (or less). Calculate (a) the number of internucleotide bonds made per minute, (b) the rate of chromosome duplication in terms of mm/min and /xm/min (assuming only one growing point), and (c) the rate at which the double helix unwinds (turns/min) during duplication. 

Brosch, R., S. V. Gordon, C. Buchrieser, A. S. Pym, T. Gamier, and S. T. Cole. 2000. Comparative genomics uncovers large tandem chromosomal duplications in Mycobacterium bovis BCG Pasteur. Yeast 17 111-23. 

Gene duplication clearly plays an important role in the evolution of LDH as it does in the evolution of dehydrogenases in general. It may be caused either by unequal crossover of chromosomes or by chromosomal duplication. 

Trask B.J., Massa H., Brand-Arpon V., Chan K.., Friedman C., Nguyen O.T., Eichler E.E., van den Engh G., Rouquier S., Shizuya H., et al. (1998). Large multi-chromosomal duplications encompass many members of the olfactory receptor gene family in the human genome. Hum. Mol. Genet. 7 2007-2020. 

Mitosis is the normal prooess of chromosome duplication which takes place every Time that a cell divides. In it, all the chromosomes are duplicated, and in the early stages of the process, the copies stick together. All of the duplicated chromosomes line up in the middle of the cell, and one of the two copies of each is pulled to either end of the cell, resulting in two complete sets of chromosomes. 

The nucleus is responsible for the direction of the metabolic activity of the cell. The key to this activity lies in the chromosomes, threadlike bodies containing a nucleic acid, deoxyribonucleic acid (DNA), and, more specifically, in the genes which are incorporated in the chromosomes. The great majority of human cells, the somatic cells, contain 23 pairs of chromosomes. The only exceptions are the gametes (sperm cells and ova), involved in reproduction, which contain only half this number. The combination of a sperm and ovum in the fertilization process produces a new cell (the zygote) with the required 23 pairs of chromosomes, which forms the basis for the new individual. Further development takes place by mitosis, or cell division, a process in which each chromosome duplicates itself prior to the cell splitting into two new cells, each of which emerges with an identical set of 23 chromosome pairs. 

In every reputable textbook it is stated that, in contrast to meiosis, mitotic division entails exact chromosome duplication. Thus, each daughter cell carries the same genetic information as the parent cell. Since we already know that DNA is the genetic material of higher organisms, we must direct our attention to the DNA when considering evidence for this statement. 

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