Mitosis predictions

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Pre-Lab Questions

1. What are chromosomes made of?

2. Research the differences that exist between mitosis and binary fission. Identify at least one difference, and explain why it is significant.

3. Cancer is a disease related to uncontrolled cell division. Investigate two known causes for these rapidly dividing cells and use this knowledge to invent a drug that would inhibit the growth of cancer cells.

Experiment 1: Observation of Mitosis in a Plant Cell

In this experiment, we will look at the different stage of mitosis in an onion cell. Remember that mitosis only occupies one to two hours while interphase can take anywhere from 18 - 24 hours. Using this information and the data from your experiment, you can estimate the percentage of cells in each stage of the cell cycle.

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Materials

Onion (allium) Root Tip Digital Slide Images

Procedure:

Part 1: Calculating Time Spent in Each Cell Cycle Phase

1. The length of the cell cycle in the onion root tip is about 24 hours. Predict how many hours of the 24 hour cell cycle you think each step takes. Record your predictions, along with supporting evidence, in Table 1.

2. Examine the onion root tip slide images on the following pages. There are four images, each displaying a different field of view. Pick one of the images, and count the number of cells in each stage. Then count the total number of cells in the image. Record the image you selected and your counts in Table 2.

3. Calculate the time spent by a cell in each stage based on the 24 hour cycle:

Hours of Stage =

24 x Number of Cells in Stage

Total Number of Cells Counted

Part 2: Identifying Stages of the Cell Cycle

1. Observe the images of the root cap tip.

2. Locate a good example of a cell in each of the following stages: interphase, prophase, metaphase, anaphase, and telophase.

3. Draw the dividing cell in the appropriate area for each stage of the cell cycle, exactly as it appears. Include your drawings in Table 3.

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Onion Root Tip: 100X

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Onion Root Tip: 100X

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Onion Root Tip: 100X

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Onion Root Tip: 100X

Table 1: Mitosis Predictions

Predictions:

Supporting Evidence:

Table 2: Mitosis Data

Number of Cells in Each Stage

Total Number of Cells

Calculated % of Time Spent in Each Stage

Interphase:

Interphase:

Prophase:

Prophase:

Metaphase:

Metaphase:

Anaphase:

Anaphase:

Telophase:

Telophase:

Cytokinesis:

Cytokinesis:

Table 3: Stage Drawings

Cell Stage:

Drawing:

Interphase:

Prophase:

Metaphase:

Anaphase:

Telophase:

Cytokinesis:

Post-Lab Questions

1. Label the arrows in the slide image below with the appropriate stage of the cell cycle.

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2. In what stage were most of the onion root tip cells? Based on what you know about cell cycle division, what does this imply about the life span of a cell?

3. Were there any stages of the cell cycle that you did not observe? How can you explain this using evidence from the cell cycle?

4. As a cell grows, what happens to its surface area to volume ratio? (Hint: Think of a balloon being blown up). How does this ratio change with respect to cell division?

5. What is the function of mitosis in a cell that is about to divide?

6. What would happen if mitosis were uncontrolled?

7. How accurate were your time predication for each stage of the cell cycle?

8. Discuss one observation that you found interesting while looking at the onion root tip cells.

Experiment 2: Tracking Chromosomal DNA Movement through Mitosis

image10.jpgAlthough mitosis and meiosis share similarities, they are different processes and create very different results. In this experiment, you will follow the movement of the chromosomes through mitosis to create somatic daughter cells.

Materials

2 Sets of Different Colored Pop-it® Beads (32 of each - these may be any color) (8) 5-Holed Pop-it® Beads (used as centromeres)

Procedure

Genetic content is replicated during interphase. DNA exists as loose molecular strands called chromatin; it has not condensed to form chromosomes yet.

Sister chromatids begin coiling into chromosomes during prophase. Begin your experiment here:

1. Build a pair of replicated, homologous chromosomes. 10 beads should be used to create each individual sister chromatid (20 beads per chromosome pair). Two five-holed beads represent each centromere. To do this...

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Figure 5: Bead set-up. The blue beads represent one pair of sister chromatids and the black beads represent a second pair of sister chromatids. The black and blue pair are homologous.

a. Start with 20 beads of one color to create your first sister chromatid pair. Five beads must be snapped together for each of the four different strands. Two strands create the first chromatid, and two strands create the second chromatid.

b. Place one five-holed bead flat on a work surface with the node positioned up. Then, snap two of the four strands into the bead to create an “I” shaped sister chromatid. Repeat this step with the other two strands and another five-holed bead.

c. Once both sister chromatids are constructed, connect them by their five-holed beads creating an “X” shape.

d. Repeat this process using 20 new beads (of a different color) to create the second sister chromatid pair. See Figure 5 for reference.

2. Assemble a second pair of replicated sister chromatids; this time using 12 beads, instead of 20, per pair (six beads per each complete sister chromatid strand).

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Figure 6: Second set of replicated chromosomes.

3. Repeat this process using 12 new beads (of a different color) to create the second set of sister chromatids. See Figure 6 for reference.

4. Configure the chromosomes as they would appear in each of the stages of the cell cycle (prophase, metaphase, anaphase, telophase, and cytokinesis). Diagram the images for each stage in the section titled “Cell Cycle Division: Mitosis Beads Diagram”. Be sure to indicate the number of chromosomes present in each cell for each phase.

Cell Cycle Division: Mitosis Beads Diagram:

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Post-Lab Questions

1. How many chromosomes did each of your daughter cells contain?

2. Why is it important for each daughter cell to contain information identical to the parent cell?

3. How often do human skin cells divide? Why might that be? Compare this rate to how frequently human neurons divide. What do you notice?

4. Hypothesize what would happen if the sister chromatids did not split equally during anaphase of mitosis.

Experiment 3: The Importance of Cell Cycle Control

Some environmental factors can cause genetic mutations which result in a lack of proper cell cycle control (mitosis). When this happens, the possibility for uncontrolled cell growth occurs. In some instances, uncontrolled growth can lead to tumors, which are often associated with cancer, or other biological diseases.

image11.jpgIn this experiment, you will review some of the karyotypic differences which can be observed when comparing normal, controlled cell growth and abnormal, uncontrolled cell growth. A karyotype is an image of the complete set of diploid chromosomes in a single cell.

Materials

*Computer Access *Internet Access

*You Must Provide

Procedure

1. Begin by constructing a hypothesis to explain what differences you might observe when comparing the karyotypes of human cells which experience normal cell cycle control versus cancerous cells (which experience abnormal, or a lack of, cell cycle control). Record your hypothesis in Post-Lab Question 1. Note: Be sure to include what you expect to observe, and why you think you will observe these features. Think about what you know about cancerous cell growth to help construct this information

2. Go online to find some images of abnormal karyotypes, and normal karyotypes. The best results will come from search terms such as “abnormal karyotype”, “HeLa cells”, “normal karyotype”, “abnormal chromosomes”, etc. Be sure to use dependable resources which have been peer-reviewed

3. Identify at least five abnormalities in the abnormal images. Then, list and draw each image in the Data section at the end of this experiment. Do these abnormalities agree with your original hypothesis? Hint: It may be helpful to count the number of chromosomes, count the number of pairs, compare the sizes of homologous chromosomes, look for any missing or additional genetic markers/flags, etc.

Data

1.

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5.

Post-Lab Questions

1. Record your hypothesis from Step 1 in the Procedure section here.

2. What do your results indicate about cell cycle control?

3. Suppose a person developed a mutation in a somatic cell which diminishes the performance of the body’s natural cell cycle control proteins. This mutation resulted in cancer, but was effectively treated with a cocktail of cancer-fighting techniques. Is it possible for this person’s future children to inherit this cancer-causing mutation? Be specific when you explain why or why not.

Pre-Lab Questions

1. Arrange the following molecules from least to most specific with respect to the original nucleotide sequence: RNA, DNA, Amino Acid, Protein

2. Identify two structural differences between DNA and RNA.

3. Suppose you are performing an experiment in which you must use heat to denature a double helix and create two single stranded pieces. Based on what you know about nucleotide bonding, do you think the nucleotides will all denature at the same time? Use scientific reasoning to explain why.

Experiment 1: Coding

In this experiment, you will model the effects of mutations on the genetic code. Some mutations cause no structural or functional change to proteins while others can have devastating affects on an organism.