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White blood cells are classified into granulocytes and agranulocytes. Granulocytes have a multi-lobed nucleus and a 'grainy' appearance. They can be further classified into basophils, eosinophils and neutrophils. Agranulocytes have a single, large nucleus which covers about 75% of the cell and can be further classified into monocytes and lymphocytes (Wikipedia, 2010).
DNA and RNA are both nucleic acids and they are made up of polynucleotides. A nucleotide consists of nitrogenous base, a pentose sugar and a phosphate unit. Genes of all organisms are made up of DNA except for some viruses which are made up of RNA. DNA is found in the nucleus and mitochondria whereas RNA is located in the nucleolus of the nucleus and the cytoplasm. DNA is a double-stranded helix while RNA is single stranded. Figure 1 shows the difference in structure for DNA and RNA. Table 1 compares the difference between DNA and RNA. Table 3 shows a comparison between the hypothesis and results of the experiment, showing that the hypothesis is the same as the results obtained. The green stains seen under the microscope indicated that DNA was present while the rose-red stains indicated that RNA was present.
The results obtained were not very desirable as the amount of DNA and RNA observed was very little. The amount of DNA and RNA was determined by the intensity of the green and rose-red colouration. The higher the intensity of the rose-red and green colouration observed under the microscope, the higher the concentration of RNA and DNA respectively.
One of the possible reasons for the low concentration of DNA and RNA could be because of the dryness of the blood sample. The blood sample might not be completely dry during the air dry process, resulting in some of the blood sample coming off when the slides were placed in solutions such as distilled water and ethanol.
In order to speed up the air-drying process of the blood smears, hair dryer was used. The use of hair dryer might result in cracks due to the high heat produced by the hair dryer. The heat produced by the hair dryer might also damage the cells, thus affecting the final result.
Only 95% ethanol is used to dehydrate the slide to prevent bacterial decay. However, it is recommended to use a series of increasing alcohol concentrations as more water would be drawn out of the cells. The full dehydration process starts off with 50% ethanol, followed by 75% ethanol, and then 90% ethanol, followed by 95% ethanol and lastly absolute (100%) alcohol.
Carnoy fixative is a slightly yellow liquid with chloroform odour that is used to rapidly penetrate the cell membrane and stop all its macromolecules to preserve the shape and structure of the cell. Other fixative that could be used includes formalin and acetic acid. Carnoy fixative contains ethanol, chloroform and glacial acetic acid in the ratio 6:3:1. Carnoy fixative is flammable due to the presence of alcohol. The Coplin jar that contained Carnoy fixative was wrapped in aluminium foil as Carnoy fixative is sensitive to light.
According to Wikipedia (2010), xylene is a clear, colourless, sweet-smelling liquid that could also be used in the experiment to make a transparent background for cells to be seen more clearly. However, the use of xylene is not recommended because xylene is carcinogenic.
The layer of blood spread onto the slides might be uneven, especially at the end of the smear as all the excess blood will gather to the end of the slide. This will result in uneven dryness of the blood smears when the smears are dried using the hair dryer and might even result in cracks in regions where the layer of blood is thin. Therefore, extra care should be taken when air drying the blood smears to ensure that no cracks were formed on the blood smears.
The control for the experiment is the slide treated with RNase + MGP. The DNase + MGP treated slide was not prepared for the experiment as only one control slide was needed. The RNase + MGP treated slide could also be replaced with a DNase + MGP treated slide depending on one's preference.
Mitochondrial DNA are found in the mitochondria which are situated in the cytoplasm. However, green stains were not seen in the cytoplasm when both slides were viewed under the microscope. This is because of the minute amount of DNA present in the mitochondria which were too small to be seen under a microscope. DNA is also located in the chloroplasts which are found in the cytoplasm of the cell. However, since we are looking at animals cells, no chloroplasts are present because chloroplasts are only found in plant cells.
RNA is also located in the nucleolus of the cell; however, no rose-red stain was seen in the nucleus when viewed under the microscope. This could be due to the small amount of RNA present in the nucleolus that is too little to be seen under the microscope. A microscope of higher magnification power is required to see the minute amount of RNA present in the nucleus.
In conclusion, two types of white blood cells were identified-granulocytes and agranulocytes. The blood smears were prepared successfully and the staining had shown the location of DNA and RNA in the cells. The results proved that RNase degrades only RNA as the RNase + MGP treated slide was stained green only. The nucleus was stained green and the cytoplasm was stained rose-red by MGP for the MGP treated slide. The hypothesis was the same as the results of the experiment. Precautions were taken when handling blood during the experiment.