Lab 8
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Thurman Young NB 1110 Thursday: 8am -10:50am Lab Report
Lab #8: Chromosome and Cell Division Thesis (Principle) – Cell division is the splitting of one cell into two, this is the process that makes growth and reproduction possible for any organism. Cell division follows a specific progression that depends on whether the cell is prokaryotic or eukaryotic. Introduction – In eukaryotic cells, DNA and associated proteins are wrapped together in packages called chromosomes. Eukaryotic cell division can take many forms depending on the chromosome structure of the cell involved. DNA in eukaryotic cells is wrapped around the proteins to form a complex called a chromatin. Throughout most of a cell’s life cycle, the chromatin is loosely packed within the nucleus. During cell division, however, the chromatin becomes highly condensed and folds up to form condensed chromosomes. DNA is always replicated, or copied, before becoming condensed. Therefore, the characteristic x shape associated with chromosomes actually represents a replicated chromosome consisting of two identical sister chromatids joined at the centromere. Unlike eukaryotes, prokaryotes do not have chromosomes. Prokaryotic DNA exists in a single loop and is not extensively folded the way eukaryotic DNA is. Chromosome number refers to the number of chromosomes within each cell of an organism. Most animals possess two nonidentical versions of every chromosome. These pairs are known as homologous chromosomes. Homologous chromosomes have the same size, shape, and function but may have slightly different versions of most genes, the basic unit of hereditary information. A pair of homologous chromosomes may both have genes for eye color, but one may have genes encoding blue eyes, while the other has genes encoding brown eyes. Cells with two sets of every chromosome between their homologous chromosomes are diploid (2n), while cells with one set of every chromosome are haploid (1n). See figure 1 as and example. Figure 1
The chromosome number of nearly every cell in the human body can be written as 2n = 46. This notation indicates that human cells are diploid, possessing 2 sets each of 23 chromosomes. The exceptions are human egg and sperm cells. These cells have a chromosome number of 1n = 23, indicating that egg and sperm are haploid and possess one set each of 23 chromosomes. The union of sperm and egg that occurs during fertilization restores the chromosome number of the resulting embryo to 2n = 46. The eukaryotic cell cycle is broken into two major phases: interphase, when the cell is not dividing, and mitotic phase, when it is. Subphases of these two phases are shown in table 1 shown below. Table 1 Subphase
Description
G1 (Growth 1)
The main development period of cell growth, during which new organelles form within the cell.
Phase
Interphase
S (Synthesis)
The cell duplicates its DNA. Cells emerge from the S phase with two identical copies of their DNA.
G2 (Growth 2)
The second period of cell growth, during which the cell prepares for the division that will take place during the mitotic phase.
Mitosis
The cell’s chromosomes, or gene-carrying structures, divide.
Cytokinesis
The cell’s cytoplasm and cell membrane divide, completing cell division.
Mitotic phase, or M phase
As they divide, cells must proceed through the various stages of the cell cycle, including the G1, G2, and M phases. All stages of the cell cycle are controlled by checkpoints. Triggers at each checkpoint assess the cell’s readiness to proceed to the next stage. Regulation also ensures that each cell obtains the proper number and type of chromosomes (packages of DNA) and organelles. Without the controlled timing of cell division, an organism would be a shapeless blob of uncoordinated cells.
Materials – Wheat germ, cold alcohol, pipettes, hot plate, beakers, test tubes, measure cylinder, spatula, detergent (Woolite), hot water, warm water, microscope, prepared slide, virgin slide and wood sticks. Methods - In this lab we removed the DNA molecules from a cell so that we could view them in detail under a microscope. We accomplished this by extracting these DNA molecules from wheat germ. We started this process by filling a large beaker with tap water and placing it on a hot plate early-on. We needed to warm the water because it aided in softening of the cell walls. After getting the water to the desired temperature we then placed about one gram of wheat germ in a large test tube. After this we added 20 mL of water. Then we used a wooden stick to gently stir the wheat germ in the water for about three minutes to soften the cell walls. The next step was to add a detergent; we used one Pasteur pipette full of Woolite as seen in Figure 2 below. Figure 2
After adding Woolite to the large test tube with the water and wheat germ, we then used the wooden stick again to stir the contents of the large test tube gently for about five more minute. We had to be careful as to not stir up bubbles due to the addition of the Woolite. After the five minutes we were ready to add the cold alcohol, in accordance with the lab procedures, we added 15 mL. When adding the cold alcohol you must tilt the test tube to a 45-degree angle and pour very slowly down the side of the test tube. The alcohol should just trickle down the side of the test tube and form a clear layer on top of the other contents in the test tube, as displayed here. We followed these steps precisely and received the results we desired.
After the addition of the cold alcohol we then placed the test tube back in the rack and allowed it to stand for approximately 15 minutes. The DNA begin precipitating between the two layer. After the 15 minutes had passed we could see a measurable amount of DNA floating at the top of the alcohol, in the test tub. This looked much like the beaker displayed on the next page in figure 3.
Figure 3
We then used our spatula to remove a DNA sample from the test tube to place on a virgin slide. We had prepared the slide for the sample earlier while waiting for the DNA to rise. We prepared the virgin slide by simply placing a circle on the bottom side of the slide. Therefore all we needed to do at this point was to place our sample in the circle on the top side of the slide and place a side cover on top of the sample. We were then ready for the microscope. We placed our sample under the microscope and view the sample under the 4X, 10X, 40X and 100X objectives. What I viewed in each objective is illustrated in figure 4 below.
Figure 4
Discussion – As we investigated the divisions of cells and what cells are made of, it has been found that all cells have a distinct finger print found in the form of DNA. This DNA can be found in the nucleus of the cell. Today we were able to remove that DNA and view it by breaking down the cell wall and allowing the DNA to be released. Conclusion – Cells must have a controlled timing for cell division, the organisms would not have structure without it. In the division of the cells the DNA must decide properly or the result is abnormalities such as Cancer or Down syndrome. References – Biology I Lab book – Symbiosos: The Benjamin Cummings Custom laboratory program for the biological sciences.
Lab #8: Chromosome and Cell Division Thesis (Principle) – Cell division is the splitting of one cell into two, this is the process that makes growth and reproduction possible for any organism. Cell division follows a specific progression that depends on whether the cell is prokaryotic or eukaryotic. Introduction – In eukaryotic cells, DNA and associated proteins are wrapped together in packages called chromosomes. Eukaryotic cell division can take many forms depending on the chromosome structure of the cell involved. DNA in eukaryotic cells is wrapped around the proteins to form a complex called a chromatin. Throughout most of a cell’s life cycle, the chromatin is loosely packed within the nucleus. During cell division, however, the chromatin becomes highly condensed and folds up to form condensed chromosomes. DNA is always replicated, or copied, before becoming condensed. Therefore, the characteristic x shape associated with chromosomes actually represents a replicated chromosome consisting of two identical sister chromatids joined at the centromere. Unlike eukaryotes, prokaryotes do not have chromosomes. Prokaryotic DNA exists in a single loop and is not extensively folded the way eukaryotic DNA is. Chromosome number refers to the number of chromosomes within each cell of an organism. Most animals possess two nonidentical versions of every chromosome. These pairs are known as homologous chromosomes. Homologous chromosomes have the same size, shape, and function but may have slightly different versions of most genes, the basic unit of hereditary information. A pair of homologous chromosomes may both have genes for eye color, but one may have genes encoding blue eyes, while the other has genes encoding brown eyes. Cells with two sets of every chromosome between their homologous chromosomes are diploid (2n), while cells with one set of every chromosome are haploid (1n). See figure 1 as and example. Figure 1
The chromosome number of nearly every cell in the human body can be written as 2n = 46. This notation indicates that human cells are diploid, possessing 2 sets each of 23 chromosomes. The exceptions are human egg and sperm cells. These cells have a chromosome number of 1n = 23, indicating that egg and sperm are haploid and possess one set each of 23 chromosomes. The union of sperm and egg that occurs during fertilization restores the chromosome number of the resulting embryo to 2n = 46. The eukaryotic cell cycle is broken into two major phases: interphase, when the cell is not dividing, and mitotic phase, when it is. Subphases of these two phases are shown in table 1 shown below. Table 1 Subphase
Description
G1 (Growth 1)
The main development period of cell growth, during which new organelles form within the cell.
Phase
Interphase
S (Synthesis)
The cell duplicates its DNA. Cells emerge from the S phase with two identical copies of their DNA.
G2 (Growth 2)
The second period of cell growth, during which the cell prepares for the division that will take place during the mitotic phase.
Mitosis
The cell’s chromosomes, or gene-carrying structures, divide.
Cytokinesis
The cell’s cytoplasm and cell membrane divide, completing cell division.
Mitotic phase, or M phase
As they divide, cells must proceed through the various stages of the cell cycle, including the G1, G2, and M phases. All stages of the cell cycle are controlled by checkpoints. Triggers at each checkpoint assess the cell’s readiness to proceed to the next stage. Regulation also ensures that each cell obtains the proper number and type of chromosomes (packages of DNA) and organelles. Without the controlled timing of cell division, an organism would be a shapeless blob of uncoordinated cells.
Materials – Wheat germ, cold alcohol, pipettes, hot plate, beakers, test tubes, measure cylinder, spatula, detergent (Woolite), hot water, warm water, microscope, prepared slide, virgin slide and wood sticks. Methods - In this lab we removed the DNA molecules from a cell so that we could view them in detail under a microscope. We accomplished this by extracting these DNA molecules from wheat germ. We started this process by filling a large beaker with tap water and placing it on a hot plate early-on. We needed to warm the water because it aided in softening of the cell walls. After getting the water to the desired temperature we then placed about one gram of wheat germ in a large test tube. After this we added 20 mL of water. Then we used a wooden stick to gently stir the wheat germ in the water for about three minutes to soften the cell walls. The next step was to add a detergent; we used one Pasteur pipette full of Woolite as seen in Figure 2 below. Figure 2
After adding Woolite to the large test tube with the water and wheat germ, we then used the wooden stick again to stir the contents of the large test tube gently for about five more minute. We had to be careful as to not stir up bubbles due to the addition of the Woolite. After the five minutes we were ready to add the cold alcohol, in accordance with the lab procedures, we added 15 mL. When adding the cold alcohol you must tilt the test tube to a 45-degree angle and pour very slowly down the side of the test tube. The alcohol should just trickle down the side of the test tube and form a clear layer on top of the other contents in the test tube, as displayed here. We followed these steps precisely and received the results we desired.
After the addition of the cold alcohol we then placed the test tube back in the rack and allowed it to stand for approximately 15 minutes. The DNA begin precipitating between the two layer. After the 15 minutes had passed we could see a measurable amount of DNA floating at the top of the alcohol, in the test tub. This looked much like the beaker displayed on the next page in figure 3.
Figure 3
We then used our spatula to remove a DNA sample from the test tube to place on a virgin slide. We had prepared the slide for the sample earlier while waiting for the DNA to rise. We prepared the virgin slide by simply placing a circle on the bottom side of the slide. Therefore all we needed to do at this point was to place our sample in the circle on the top side of the slide and place a side cover on top of the sample. We were then ready for the microscope. We placed our sample under the microscope and view the sample under the 4X, 10X, 40X and 100X objectives. What I viewed in each objective is illustrated in figure 4 below.
Figure 4
Discussion – As we investigated the divisions of cells and what cells are made of, it has been found that all cells have a distinct finger print found in the form of DNA. This DNA can be found in the nucleus of the cell. Today we were able to remove that DNA and view it by breaking down the cell wall and allowing the DNA to be released. Conclusion – Cells must have a controlled timing for cell division, the organisms would not have structure without it. In the division of the cells the DNA must decide properly or the result is abnormalities such as Cancer or Down syndrome. References – Biology I Lab book – Symbiosos: The Benjamin Cummings Custom laboratory program for the biological sciences.
