To What Extent Is The Cell Cycle Fundamental To The Development Of Eukaryotic Organisms

Mitosis is a component of the cell cycle, in which cells replicate to form two identical daughter cells, so that the total number of chromosomes is maintained, for growth, repair and asexual reproduction. Therefore, mitosis is essential in maintaining genetic continuity between generations of cells. Mitosis is composed of prophase, metaphase, anaphase, and telophase. ;However, before mitosis begins, the cell must first undergo interphase, during which it grows and its DNA replicates. The chromosomes then condense to form chromatin; sister chromatids align at the equator of the cell and finally, during cytokinesis, the cytoplasm divides, producing two genetically identical daughter cells.

All multi cellular organisms contain a range of specialised cells, designed to carry out a specific function. In order for a cell to become specialised, a process called differentiation occurs, where stem cells (undifferentiated cells that are genetically identical with the ability to differentiate into any cell) produce cells with specialised structures. It is during interphase that cells specialize through a process where genes are selectively activated or deactivated. How this occurs is through a process known as histone modification. This includes methylation, which typically decreases the likelihood of a gene being transcribed and therefore represses the gene. Acetylation on the other hand opens up the chromatin structure, so that RNA polymerase is better able to access the gene and transcribe it, activating the gene. ;The cell cycle is therefore fundamental in the development of eukaryotic organisms, as specialised cells are needed to form whole tissues, which work together to form organs, which then finally make up organ systems, ensuring that there is no conflict in the functioning of cells to perform specific tasks, vital for carrying out the vital processes for eukaryotic organisms to survive.

Checkpoints in mitosis regulate the progress of the cell cycle, ensuring that each step is only performed once, and in the correct sequence, therefore preventing the transmission of genetic errors to daughter cells. Cancer is characterised by the uncontrolled replication of mutated cells; hence it is vital that mitosis is regulated to prevent this. These checkpoints are necessary in controlling genetic instability.

In the semi conservative replication of DNA, the double helix is un winded and hydrogen bonds between complementary bases are broken. Free DNA nucleotides are joined to the exposed bases of the template strand, where DNA polymerase then connects adjacent nucleotides in condensation reactions. ;Therefore the newly formed DNA will contain one strand from the original template and one that is newly synthesized. As mentioned previously, DNA replication is vital in interphase (and more specifically the S phase) before mitosis. ;Eukaryotic organisms rely on each daughter cell receiving identical genetic information during processes like growth and repair. Any mutations that occur during this process could result in dysfunctional cells and potentially cause disease.

Mitosis allows for asexual reproduction, where genetically identical offspring are produced. In some aspects asexual reproduction can be advantageous opposed to sexual reproduction as only one parent cell is required, unlike sexual reproduction which requires two parent cells where gametes are fused. Therefore, offspring can be successfully created without the need for a partnership, making it a far more efficient process as less energy or time is needed. This allows a population to rapidly increase when conditions are favourable/stable, making it essential for eukaryotic organisms to develop as all the offspring will be adapted to that environment.

On the other hand, meiosis allows for sexual reproduction, needed to ensure genetic variation in offspring. This is achieved through two processes known as crossing over and independent assortment. In crossing over, genetic information is exchanged between homologous chromosomes producing new combinations of maternal and paternal alleles, therefore generating genetic variation. Independent assortment allows for various combinations to be made in the distribution of maternal and paternal alleles in the daughter cells. Meiosis therefore allows for genetic variability in daughter cells, allowing for natural selection. Those that have inherited an allele that is favourable to the environment are more likely to survive and reproduce, passing on that allele to the following generation. This allele will eventually increase in the gene pool. Meiosis is vital for the development of eukaryotic organisms that are exposed to changing environments as they are allowed to adapt.