How Do Different Stages of The Cell Cycle Work

Introduction

In this lab we looked at cells that where exhibiting different stages of the cell cycle and mitosis using appropriate aseptic technique. The cell cycle refers to the development and reproductive process a cell goes through. According to The Biology Project by the University of Arizona the cell cycle is defined as, “The cell cycle is an ordered set of events, culminating in cell growth and division into two daughter cells. Non-dividing cells not considered to be in the cell cycle”( the Biology Project).

The cell cycle has 5 stages. G1, S, and G2, which is part of interphase, where genetic material replicates and the cell increases in size. M phases is where the cell divide completely. G0 refers to a cell in a dormant state, it is neither growing nor dividing and might not ever. The M phase contains multiple phases within it, representing the stage of division the cell is in. According to a lecture by Dr. Beaster-Jones M phase consists of Prophase, Prometaphase, Metaphase, Anaphase, and Telophase followed by Cytokinesis. Prophase is the beginning stage of the M phase, the nuclear membrane dissociates into smaller vesicles and the chromatids become highly compacted. Prometaphase consists of the formation of the meiotic spindle, and the interaction of the spindle fibers with the chromatids. Metaphase is characterized by the alignment of chromatids along the middle of the cell across the metaphase plate in a single row. In the Anaphase stage, the chromatids begin to be pulled toward the poles of the cell by the microtubules. In Telophase two nuclei form and the nuclear envelope reforms along with the beginning of a cleavage furrow/cell wall. Cytokinesis is where the cell fully divides into two full daughter cells when the cytoplasm divides.

The cell cycle acts as a checks and balances system for cell division. Without it cells would grow uncontrolled resulting in cancerous and noncancerous tumors and other deformities and issues. The following terms refer to regulations in the cell cycle according to The Biology Project, “Cdk (cyclin dependent kinase, adds phosphate to a protein), along with cyclins, are major control switches for the cell cycle, causing the cell to move from G1 to S or G2 to M.MPF (Maturation Promoting Factor) includes the CdK and cyclins that triggers progression through the cell cycle. P53 is a protein that functions to block the cell cycle if the DNA is damaged. If the damage is severe this protein can cause apoptosis (cell death) (The Biology Project). A p53 mutation is the most common mutation that leads to cancer. In some individuals, a genetic defect leads to a higher risk of p53 mutation, like Angelina Jolie, and preventative measures are sometimes taken. People with this genetic defect experience higher rates of cancer.

Meiosis is the cell division reserved for sex cells, or gametes. Meiosis has two rounds of chromosome manipulations and cell divisions compared to Mitosis’ one division. Meiosis ensures genetic diversity as only one set of chromosomes of the parent is passed on through each gamete, ensuring a mix of both parent’s genetic material in the offspring. Female sex gamete’s have XX chromosomes and XY chromosomes. Because of this a lot of genetic disorders are sex linked, meaning they are inherited through the X or Y chromosome. Sex linked genetic disorders that stem from the X chromosome are far more common in men, as they inherit only one X chromosome, and females inherit two X chromosomes, which helps to offset the effect of the genetic disorder.

Both of these forms of reproduction are pertinent to all forms of life. In this lab we learned how to properly identify each stage that a cell might be in and how to correctly prepare an agar plate and to prepare slides of samples.

Methods and Results

This study was conducted in one of the laboratory in the Science and Engineering Building at UC Merced. Students were given models of cells in different stages of Mitosis and asked to put them in order from the beginning to end. Then Students were given a petri dish with agar. We had black and tan strains of Sordaria, and were supposed to compare them. Making sure not to open the petri dish lid, we labeled the bottom of the dish like so:

The plus signs represent the wild type strain, or the black strain while the minus signs represent the mutant strain, which is the white strain. We applied the two strains by first sterilizing the inoculation loop by dipping alcohol then passing it over the Bunsen burner until it turned red, then let it cool for 10 seconds. Then we applied the wild type strain to the plate by scooping up a small amount of the mycelium and transferring it unto the plus signs on our petri dishes. Then we reheated the inoculation loop, and repeated the steps except with the mutant type, which was applied to the area marked with the minus signs on the dish. Our dish was then given to the instructor.

The next part of the lab was an examination of the cell count of am onion root tip from a prepared slide. Using a light microscope we examined the prepared slide, and attempted to identify the different stages 200 separate cells where in at the time the slide was prepared. We found that a large amount of cells were in the interphase stage, and amount of cells in each stage almost seemed to decrease as we observed cells in the last few stages.

The last section of the lab we prepared our own slide of the onion root tip. We clipped the end of a root of the bulb, then placed it onto a slide. Then, we covered the rip of the root with 2 drops of HCL, and heated the slide over the alcohol lamp by passing the slide over the heat once every 2 seconds for 30 seconds while using a clip to hold the slide. Then we let the slide cool for 10 minutes, and since it didn’t dry out, we didn’t need to add more HCL. We then added 2 drops of Toluidine Blue to the tip of the onion root and let it stand for 2 more minutes, and since it didn’t dry out at the end of the two minutes we didn’t have to reapply the Toluidine Blue. We then rinsed the root with the dH2O provided. Then we added one drop of water to the slide and applied the cover slip. We gently smooshed the over slip and the root to spread the root tissue. The first time we examined the root we examined it on low power, then we increased the magnification to view the stages of mitosis. We had a difficult time observing any of the stages of mitosis, may have been due to us overdyeing the root or squashing it too much.

Discussion

During this experiment we compared the prepared slides cells, to our own slide that we prepared. The slide that was provided by the lab instructor was easier to examine then our slide. This was due to the fact that ours slide appeared to be entirely in Interphase, whereas the prepared slide had clearly defined stages of the cell cycle. This may be the result of over dying, or squashing the root too much. This means that our cells might have died through apoptosis, or cell death caused by over staining the slide. This is why we counted the pre-prepared slide’s cell count, instead of our slides as ours was extremely unclear, and we would have been unable to identify any stages of the cell cycle except Interphase.

In the pre-prepared slides examination, we looked at the number of cells in each stage of the cell cycle. We found that the majority of the cells in Interphase, which may be because cells spend most of their “time” in the Interphase stage. As each stage was examined in order, less and less cells appeared in them. This may be because of the time the cell spent in each stage, or other factors. It was much easier to view this slide than our own slide overall due to the lack of clarity in our slide.

Conclusion

The purpose of this lab was to determine the differences between meiosis and mitosis, and be able to determine what stage in the cell cycle a cell was in. We compared a slide we prepared and a slide given to us by the lab structure, and found that our slide was not reliable due to the fact that all of our cells was in interphase however, the other slide showed that interphase had the most cells, and the number of cells decreased in each stage as it moved through the cell cycle.