Access to DNA is required to regulate the gene expression, and this access regulated by many factors such as chromatin remodeling or histone modification. According to Vogel-Ciernia and Wood (2014), chromatin remodeling is a movement of nucleosomes along DNA by the aid of chromosome remodeling complexes (CRCs) that is composed of four large protein families which are BAF (SWI/SNF), INO80/SWR1, ISWI or NURF, and CHD or NuRD. CRCs are interacting with DNA and nucleosomes then broke contacts of nucleosomes to evict or exchange nucleosomes and changing its location along DNA by hydrolyzing ATP. They convert energy that comes from the hydrolysis of ATP to energy that is required for the movement of the nucleosome (Phillips & Shaw, 2008). These CRPs facilitate gene expression by altering the chromatin structure. Generally, each nucleosome has DNA-binding site that is inaccessible hence remodelers have to be used to get access to these inaccessible sites to enable transcription, DNA repair etc. (Philips et al., 2008). For example, SWI/SNF complexes regulate binding of transcription factors by disrupting nucleosomes to allow the binding of transcriptional activators such as GAL4 proteins to the core nucleosome (Kwon, Imbalzano, Khavari, Kingston & Green, 1994). To sum up, chromatin remodeling which is a changing of the location of nucleosomes facilitate the gene expression.
We prepare a slide from the tip of onion root to observe phages of mitosis. Firstly, we cut tips of the root of onion and there is a two main reason for using onion root. One of them is that onion is colorless, so when we stain it with acetocarmine, observation of chromosomes become easy. The second reason is that the tip of the root of plants are always growing as they search for water and nutrients. Hence the possibility of finding different phases of mitosis become easy. Also, we use more than one onion in the laboratory to increases our chance. Then we incubate them in HCl to get rid of the cell wall since they block the entry of dye into the cell. After that, we incubate it also in distilled water to remove the HCl since if we don’t remove HCl, it will harm to cell and can destroy it completely. Then we dissolve the carmine powder in acetic acid to make possible the entry of the powder into the cell because powder cannot enter the cell since its big. Also, we heat it and evaporate the acetic acid because when we do this, dissolved carmine powder stack to the chromosomes and stain it. After all, we prepare a slide by using one of these tips. While preparing the slide, unlike the normal slide preparation, we press onto the slide to decreases the layers because if there is more than one layer, observation becomes hard.
We observed telophase and prophase. We can distinguish the prophase stage since there is no nuclear membrane and the chromosomes condensed. Since there are two nuclei that are separated from each other with a cell template, we can observe telophase. Sister chromatids which look like fingers pulling to the opposite side of the cell, so we can say that it is the anaphase stage. We observe that the chromosomes line about an equatorial plane, so we can suggest that these are metaphase stage of mitosis. We observe nuclear membrane still there and condensed chromosomes cannot be seen, so we can say that the cell is in the interphase which is not a stage of mitosis, actually, it is a preparation for mitosis.
Before doing this experiment, I expect that we can see all the phages of mitosis very easily. But, we couldn’t. We observe only telophase and prophase stages. Also, ı thought that all stages are in the one shape, so ı expect that when we saw them, we be able to distinguish them easily. For example, ı thought that in metaphase, we always see a perfect equatorial plane. But there was not the case. Actually, distinguish phages from each other is hard since there are also stages like pre-metaphase or late-prophase.
- Phillips T. (2008). Chromatin Remodeling in Eukaryotes. Retrieved from https://www.nature.com/scitable/topicpage/chromatin-remodeling-in-eukaryotes-1082
- Kwon H., Imbalzano A.N., Khavari P.A., Kingston R.E., Green M.C. (1994, August 11). Nucleosome disruption and enhancement of activator binding by a human SW1/SNF complex. Retrieved from https://www.nature.com/articles/370477a0
- Vogel-Ciernia A., Wood M.A. (2014, May). Neuron-specific chromatin remodeling: A missing link in epigenetic mechanisms underlying synaptic plasticity, memory, and intellectual disability disorders. Retrieved from https://www.sciencedirect.com/science/article/pii/S0028390813004759#bib28
- Mitosis in Onion Root Tips. (n.d.). Retrieved from http://vlab.amrita.edu/?brch=188&cnt=1&sub=3&sim=1102