Precise chromosomal DNA replication during S phase of the cell cycle is a crucial factor in the proper maintenance of the genome from generation to generation. The current “once-per-cell-cycle” model of eukaryotic chromosome duplication describes a highly coordinated process by which temporally regulated replicon clusters are sequentially activated and subsequently united to form two semi-conserved copies of the genome. Replicon clusters, or replication domains, are comprised of individual replication units that are synchronously activated at predetermined points during S phase. Bi-directional replication within each replicon is initiated at periodic AT-rich origins along each chromosome. Origins are not characterized by any specific nucleotide sequence, but rather the spatial arrangement of origin replication complexes (ORCs). Given the duration of the S phase and replication fork rate, adjacent origins must be appropriately spaced to ensure the complete replication of each replicon. Chromatin arrangement by the nuclear matrix may be the underpinning factor responsible for ORC positioning. The six subunit ORC binds to origins of replication in an ATP-dependent manner during late telophase and early G1. In yeast, each replication domain simply contains a single ORC binding site. However, more complex origins are characterized by an initiation zone where DNA synthesis may begin at numerous locations. A single round of DNA synthesis at each activated origin is achieved by “lic...
The fungus Sordaria fimicola is commonly used to study the different processes of cell cycles such as the assortment of genes and the crossing over during meiosis. Considering the importance of genetics in the world today, this experiment is crucially valuable in helping the students gain knowledge in the different processes of cell cycle and learning how to attempt similar experiments on their own in the future. Sordaria fimicola requires “both mitotic and meiotic nuclear divisions to manufacture eight haploid ascospores” (Helm, 1998). This fungus “spend most of its life in haploid condition” (Glase, 1995). When the haploid nuclei fuse together in the cells, they beco...
Trisomy 13 or Patau Syndrome” Trisomy 13 is a genetic disorder found in babies. It is also called Patau syndrome in honor of the physician who first described it, Krause Palau. Trisomy 13 is a genetic disorder in which there is three copies of chromosomes on Chromosome 13. Patau first described the syndrome and its involvement with trisomy in 1960. It is sometimes called Bartholin-Patau syndrome, named in part for Thomas Bartholin, a French physician who described an infant with the syndrome in 1656.
The location of genomes in both prokaryotes and eukaryotes show major discrepancies because they have different levels of cell organization. Due to the simplicity of the prokaryotes, they lack membrane bound organelles such the nucleus. Therefore, genomes of the prokaryotes reside as irregular Protein and deoxyribos nucleic acid (DNA) complex in cytosol (liquid portion of cytoplasm). This area of the cytoplasm is defined as the ‘nucleoid’ (Bauman.R 2004). Unlike Eukaryotes, it does not possess a nuclear envelope.
During interphase, cell growth, DNA replication, separation of centrioles and protein synthesis takes place. This phase is acknowledged to being the most extensive period of the cell cycle thus signifying the stage in which the cell devotes th...
RNAi, DNA and chromatin modification are involved in heterochromatin formation and gene regulation and genome stability.
Mechanisms and Functions of ATP-Dependent Chromatin-Remodeling Enzymes Geeta J. Narlikar, Tom Owen-Hughes Email DOI: http://dx.doi.org/10.1016/j.cell.2013.07.011
Rather than the recruitment of DSB repair proteins to DNA damage sites for repair as part of the damage response, nuclear foci of Rad50/Rad51 did no colocalize with the γ-H2AX foci in HGPS cells. Although all other elements of the damage response system such as the ATR and ATM checkpoints and Chk1 and Chk2, the critical components for repair of DNA DSBs and the resting of stalled replication forks, were not activated. Failure to recruit repair factors to DNA damage sites result in irreparable DNA damage in HGPS cells.
Cloning (asexual reproduction) is the production of individuals who are genetically identical to an already existing individual. The procedure is called somatic cell nuclear transfer. Scientists take a mature, unfertilized egg and remove its nucleus. Next, they, introduce a nucleus obtained from a specialized (somatic) cell of an adult organism. Once the egg begins to divide, they transfer the embryo into woman's uterus to initiate a pregnancy. Since almost all the hereditary material of a cell is contained within its nucleus, the re-nucleated eggs are genetically identical to the organism that was the source of the transferred nucleus (Kass, 2001). The genetically identical individual is called the clone and could be produced by nuclear transfer. Any person, living or deceased could be cloned, and in any number. Due to the fact that cloning requires no personal involvement on the part of the person whose genetic material is used, cloning could be completed without a person’s consent. This would be a threat to reproductive freedom, according to Kass.
DNA supercoiling occurs in all cells that undergo genetic processing. This event blocks replicative and transcriptional machinery from binding to the DNA helix, which proves detrimental to the cell. However, current research is beginning to show that not all affects of supercoiling produce negative results. These studies prove that different coiling patterns increase the efficiency of epigenetic processes such as methylation and acetylation. Topoisomerase, a post-transcriptional monomeric enzyme, solves the winding problem of the double helix by implementing transient cuts in the genome. As these cuts build up, the genome is essentially fragmented by the enzyme and the cell is unable to express essential genes; this genomic degradation by topoisomerase serves as a viable pathway into cancer research. This review article synthesizes the many ideas surrounding topological cellular events, and presents a new direction for research on chromatin modification in cancerous cells. However, due to the time constraints of the project, this article will not thoroughly discuss the mechanistic process of the replication pathway.
A chromosome is made up of two identical structures called chromatids. The process of nuclear division is called interphase; each DNA molecule in a nucleus makes an identical copy of itself. Each copy is contained in the chromatid and a characteristic narrow region called the centromere holds the two chromatids together. The centromere can be found anywhere along a chromosome but the position is the characteristic for a particular chromosome. Each Chromatid contains one DNA molecule. DNA is the molecule of inheritance and is made up of a series of genes. The fact that the two DNA molecules in the sister chromatids, and hence their genes, are identical is the key to precise nuclear division.
Past research has shown increases in the recombination rates due to environmental stressors including age, food availability, behavioral stresses, chemicals and most importantly temperature. This study looks at the effects of an increase in incubation temperature on recombination rates in Drosophila melanogaster. A wildtype parent for three genes (al+ dp+ and b+) was crossed with a recessive parent (al dp b). These genes included presence of aristala, wing type and body color, all found on the second chromosome. The parents were mated and the organisms were divided into two different vials each placed in a different temperature; one in 25°C and the other in 30°C. The offspring were counted based on their phenotype for the three studied traits. It was predicted that there would be an increase
The two new pair of centrioles arise from the proximal end of each of the older centrioles, and elongate to reach the same length as the parent centrioles. The original mother and daughter centrioles completely separate from each other, along with their new daughter centrioles to form two new centrosomes. Each of the two resulting centrosomes thus contain one centriol from the older generation and one newly formed centriole (semiconservative replication). The PCM also gets divided between the two new centrosomes. The sequence of steps of the centrosome duplicaiton cycle shows variations in some cells. For example, in Drosophila melanogaster embryo, the PCM divides before the new daughter centrioles are
permanently in the G1 phase. Next is the S phase, in which the mass of
During prophase I, homologous chromosomes pair and form snynapses. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. The bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.
During this phase the DNA aka “deoxyribose nucleic acid” clone then forms chromatin. Chromatin is the mass of genetic material that forms into chromosomes. Interphase is divided into smaller parts: G1 Phase, S phase and G2 Phase. Throughout all the phases, the cells continuously develop by producing mitochondria, endoplasmic reticulum, and proteins. The actual division occurs during the S phase bur the G phases are mainly for the purpose of growing. Starting with the G1 phase the cell grows in preparation for certain intracellular components and DNA replication. This phase makes sure the cell is prepared for the process of DNA replication. It reviews the size and environment to ensure that is it ready to go, and cannot leave the G1 until it is complete. But what happens to a cell when it is not complete and cannot exit out of the phase? It will pause and transfer to phase G0. There’s no certain time to be in this phase but it will remain until it reaches the fitting size and is in a supportive surroundings for DNA replication. It will exit either G1 or G0 and there is no other way besides these. Then the cell will advance to the next phase which is the S phase. Synthesis, or more known as S phase is the section of the cell cycle when the DNA is wrapped into chromosomes then duplicated. This is a very important part of the cycle because it grants each of them that is created, to have the exact same genetic