INTRODUCTION To divide, a cell must grow, replicate its genetic material (DNA), and split into two daughter cells. Cells perform these tasks in an organized series of steps that make up the cell cycle. In eukaryotic cells, or cells with a nucleus, the stages of the cell cycle are divided into two major phases: interphase and the mitotic (M) phase. • During interphase, the cell grows and makes a copy of its DNA. • The mitotic (M) phase, divides the cell DNA into two sets and its cytoplasm, forming two new cells.
At the end of G2, a second checkpoint, the G2 Checkpoint, will occur to determine if I can now proceed and enter into the next stage, mitosis. Mitosis contains its own five individual stages: prophase, prometaphase, metaphase, anaphase, and telophase. During prophase, my chromosomes become visible as paired sister chromatids and my nuclear envelope disappears. Sister chromatids are replicated chromosomes that form an X shape thanks to the centromere. They are identical pieces of DNA.
On the last phase, telophase I, the daughter cells completely divide, chromosomes disappear, and the nucleic membranes forms. Meiosis II also have the four phases in meiosis I. First at prophase II, centrioles form spindle fibers as nuclear membrane disappears and chromosome become more visible entering into metaphase II where chromosomes again line up at the middle along the spindle fibers. In anaphase II, the chromosomes split into two chromatids each containing a DNA strand then the cell divides. Lastly, the nucleic membrane forms creating four new cells each with distinct DNA.
Basic Stages in an Animal Development Animal development is the process that leads to the formation of a new animal or organism from cells that derived from one or more parent individuals. Animal or organism arises through a process that begins with the fertilized egg and ends with a new individual. The fertilized egg will undergo cell divisions to increase the number of cells and simultaneously the cells produced will differentiated into organs and organs systems of the fully formed organism. Animal will go through six basic stages of development. They are fertilization of egg (ovum) and sperm, cleavage, gastrulation, neurulation, organogenesis and metamorphosis (refer to Figure 1 in Appendix 1).
According to MicroPop yeast can reproduce sexually in this way: In sexual reproduction, a single yeast cell undergoes meiosis and produces haploid spores; these spores can recombine with other haploid spores, producing a diploid cell – the yeast’s “normal” state. And lastly stated by BBC: Like bacteria, yeast cells reproduce asexually. However, they do this by producing a bud. This is a new cell that eventually breaks away from the parent cell. The growth rate of a yeast
Cell Division As a eukaryotic organism grows, cells divide and create new cells based on its DNA. This is called cell division. Cell division is the process when a parent cell divides into two or more daughter cells. Cell division occurs as part of the cell cycle. The two types of cell division processes are mitosis and meiosis.
To increase the size of DNA fragments used in transgenesis, scientists are cloning them in yeast or bacterial artificial chromosomes (YACs and BACs). This has increased the use of transgenic mice as disease model. Single Gene Knock-Outs and Knock-Ins These are models to target a mutation to a specific gene locus and are particularly useful if a single gene is shown to be the primary cause of a disease. Knock-out mice carry a gene that has been inactivated while knock-out mice are produced by inserting a transgene at the exact location where it is overexpressed. Many knock-out and knock-in mice have similar, if not identical phenotype to human patients and are therefore good models for human
Through the reverse transcription, the viral RNA is transcribed to viral double-stranded DNA. This process is catalyzed by an RNA-dependent DNA polymerase, also known as reverse transcriptase, which is encoded by the viral genome, which is integrated within the cell genome by integrase. This protein cleaves nucleotides of each 3’ ends of the double helix DNA creating two sticky ends, transfers the modified provirus DNA into the cell nucleus and facilitates its integration into the host genome. The integration of proviral DNA and the expression of the provirus require that target cell is in an activated state. Monocytes/macrophages, microglial cells, and latently infected quiescent CD4+ T-cells contain integrated provirus and are important long-living cellular reservoirs of HIV.
To transfer genes, scientists use yeast cells instead of bacteria because yeast cells are eukaryotic and they can translate genes from other eukaryotes. To transfer DNA, a vector is used in genetic engineering is a carrier. Bacteria contain vectors called plasmids, which are small circular pieces of DNA within the bacteria. An example in medicine would be diabetes. Before genetic engineering was common, doctor’s cures diabetes with animal insulin obtained from farm animals, but that used to cause allergic reactions in some patients.