Eukaryotes duplication

Eukaryotic ceils possess a discrete, membrane-bounded nucleus, the repository of the cell s genetic material, which is distributed among a few or many chromosomes. During ceil division, equivalent copies of this genetic material must be passed to both daughter ceils through duplication and orderly partitioning of the chromosomes by the process known as mitosis. Like prokaryotic... 

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. 

Many important details have emerged concerning the mechanisms of DNA replication in both bacteria (Prokaryotes) and higher cells (Eukaryotes). These mechanisms are vital in understanding how a cell duplicates its genetic material (DNA), and how this duplication is related to cell division. For these reasons, cells have evolved elaborate mechanisms to ensure that the process of duplication (DNA replication) is error free. This level of control is so important that cells will actually cease cell division if errors become too frequent and wait until the DNA is repaired. 

Eukaryotic chromosomes are detectable by light microscopy at the stage just prior to cell duplication. At this... 

Mitosis and cell division in eukaryotes. After DNA duplication has occurred, mitosis is the process by which quantitatively and qualitatively identical DNA is delivered to daughter cells formed by cell division. Mitosis is traditionally divided into a series of stages characterized by the appearance and movement of the DNA-bearing structures, the chromosomes. (a) Premitosis, (b) through (h) Successive stages of mitosis, (/) Postmitosis. 

From the complementary duplex structure of DNA described in chapter 25, it is a short intuitive hop to a model for replication that satisfies the requirement for one round of DNA duplication for every cell division. In chapter 26, DNA Replication, Repair, and Recombination, key experiments demonstrating the semiconservative mode of replication in vivo are presented. This is followed by a detailed examination of the enzymology of replication, first for how it occurs in bacteria and then for how it occurs in animal cells. Also included in this chapter are select aspects of the metabolism of DNA repair and recombination. The novel process of DNA synthesis using RNA-directed DNA polymerases is also considered. First discovered as part of the mechanisms for the replication of nucleic acids in certain RNA viruses, this mode of DNA synthesis is now recognized as occurring in the cell for certain movable genetic segments and as the means whereby the ends of linear chromosomes in eukaryotes are synthesized. 

The nuclei of eukaryotic cells contain multiply coiled DNA bound with proteins in bodies called chromosomes. The number of chromosomes varies with the organism. Humans have 46 chromosomes in their body cells (somatic cells) and 23 chromosomes in each germ cell, the eggs and sperm that fuse to initiate sexual reproduction. During cell division, each chromosome is duplicated and the DNA in it is said to be replicated. The production of duplicates of a molecule as complicated as DNA has the potential to go wrong and is a common mode of action of toxic substances. Uncontrolled cell duplication is another problem that can be caused by toxic substances and can result in the growth of cancerous tissue. This condition can be caused by exposure to some kinds of toxicants. 

Before one cell can divide into two cells, the cell must make a copy of the cellular DNA so that after cell division, each cell will contain a complete complement of the genetic material. Replication is the cellular process by which DNA or the cellular genome is duplicated with almost perfect (and sometimes perfect) fidelity. The replicative process in prokaryotic cells, such as Escherichia coli (E. coli) cells, is best understood and will be described in detail, and the aspects that differ in replicating eukaryotic cells will be noted. 

Huet J, Schanbel R, Sentenac A, Zillig W (1983) Archaebacteria and eukaryotes posess DNA-dependent RNA polymerases of a common type. EMBO J 2 1291-1294 Iwabe N, Kuma KI, Hasegawa M, Osawa S, Miyara T (1989) Evolutioanry relationship of archaebacteria, eubacteria, and eukaryotes inferred from phylogenetic trees of duplicated genes. Proc Natl Acad Sci USA 86 9355-9359... 

---