The Mitotic Cell Cycle

Place the letters representing the individual cells in the correct sequence of the mitotic cell cycle. The first letter has already been filled in.

Cell A in Fig. 6.1 is in one of the main stages of mitosis.

Describe the events that occur during this main stage of mitosis.

Complete Table 6.1 by stating the term that matches each of the descriptions.

Table 6.1

Changes occur to chromatin during mitosis so that chromosomes become visible.

State what happens to chromatin so that individual chromosomes can be seen during mitosis.

Fig. 5.1 is a transmission electron micrograph of two human chromosomes at metaphase of mitosis.

Describe the structure of chromosomes at metaphase, such as the two chromosomes shown in Fig. 5.1.

Some of the structures shown in Fig. 6.1 contain DNA.

Use a line labelled D on Fig. 6.1 to indicate one of these structures.

Name the stage of mitosis shown in Fig. 6.1.

Colchicine is a chemical used by scientists to study mitosis. This chemical inhibits the organisation of the microtubules in prophase of mitosis.

The cell shown in Fig. 6.1 had not been treated with colchicine.

Explain the evidence in Fig. 6.1 that shows the cell had not been treated with colchicine.

Identify the stages of mitosis occurring in the cells labelled B and C in Fig. 1.1.

B ______
C ______

Describe the behaviour of the chromosomes in the stage of mitosis shown in cell A in Fig. 1.1.

Cell D in Fig. 1.1 is in interphase.

Describe the role of DNA ligase in interphase.

State the location of telomeres on a chromosome.

Some people with a long lifespan have cells showing a higher than normal activity of telomerase.

Suggest why a long lifespan could result from a higher telomerase activity.

In interphase, individual chromosomes are too diffuse (long and thin) to be visible using a microscope. In this stage, the chromosomal material is known as chromatin.

State the term used to describe the proteins that are complexed with DNA and form part of chromatin.

When viewed through a microscope, a chromosome is most clearly visible during the metaphase stage of mitosis.

Complete Fig. 1.1 to produce a labelled diagram of the metaphase stage of mitosis in an animal cell with two chromosomes.

Outline the changes that occur to the structure and behaviour of a chromosome:

• from the start of the S phase to the end of interphase
• during prophase of mitosis.

Name the stage of mitosis shown in Fig. 2.1.

Fig. 2.2 shows the cell in Fig. 2.1 at the start of cytokinesis.

Complete Fig. 2.2 to show the daughter chromosomes in each nucleus.

State the role of telomeres during DNA replication.

Multiple myeloma is a type of cancer in the bone marrow where some of the stem cells start to produce abnormal blood cells.

• One treatment is to collect stem cells from the bone marrow of the person with multiple myeloma. Healthy stem cells are isolated and grown in the laboratory.
• Radiation is then used to destroy all stem cells and cancerous cells in the bone marrow.
• Finally, large numbers of the healthy stem cells grown in the laboratory are returned to the bone marrow.

Suggest the role of stem cells in this treatment of multiple myeloma.

Name the stage of mitosis shown in cell Q.

Outline the roles of mitosis in a healthy plant.

Uncontrolled mitosis can cause cancer in humans. Paclitaxel is a drug used in the treatment of some forms of cancer.

Researchers investigated the effect of Paclitaxel on the mitotic cell cycle of cancer cells.

• The cancer cells were grown for two days and then divided into groups.
• Each group was treated with a different concentration of Paclitaxel.

After 28 hours (one cell cycle):

• the percentage of cells in stages of mitosis was calculated
• the ratio of the number of cells in anaphase to the number of cells in metaphase was determined.

The results of the investigation are shown in Fig. 6.2.

With reference to Fig. 6.2, describe the results and suggest an explanation for the effect of Paclitaxel on the mitotic cell cycle.

Name the stage of mitosis in cell A and in cell B, shown in Fig. 4.1.

A = ______
B = ______

Fig. 4.1 shows microtubules in the cells that are dividing.

Describe the role of microtubules in mitosis.

State what happens in cell C, shown in Fig. 4.1, until two new cells are formed.

The cells produced in the developing whitefish are genetically identical.

Identify and explain two events that occur during the cell cycle that lead to daughter cells being genetically identical.

Complete Table 2.1 by stating one feature, visible in Fig. 2.1, that is used to identify each stage.

Table 2.1

Draw a labelled diagram to show one chromosome at metaphase of mitosis.

On the chromosome you have drawn add labels to show:

• the position of a telomere
• a chromatid
• the centromere.

State the type of protein that is associated with DNA in chromosomes.

Describe how the spindle is involved during the process of mitosis.

Complete Table 6.1 to show the correct order of stages in the mitotic cell cycle.

Some of the stages have been completed for you.

At various points during the mitotic cell cycle, checks are made. A cell goes through cell death (apoptosis) if errors occur that cannot be repaired. This makes sure that the daughter cells produced are genetically identical to each other and to the original cell.

Drugs have been developed that can inhibit the mitotic cell cycle and cause the cell to carry out apoptosis. These drugs are used in the treatment of cancer.

Vincristine and 5-fluorouracil are chemical compounds that act as cell cycle inhibitors and can lead to apoptosis.

• Vincristine binds to spindle microtubules and prevents the spindle from carrying out its function.
• 5-fluorouracil prevents the synthesis of thymine nucleotides.

Complete Table 6.2 to show which event in the cell cycle will occur when Vincristine or 5-fluorouracil are added to healthy dividing cells at the start of the interphase stage of the cell cycle.

Place a tick ($\checkmark$) if the event will occur or a cross ($\times$) if the event will not occur.

All boxes in the table should be completed.

Table 6.2

Vincristine has been used in the treatment of certain types of leukaemia.

Fig. 6.1 is a photomicrograph of a blood smear of a person with one form of leukaemia, which affects lymphocytes.

Describe how:

• the blood smear shown in Fig. 6.1 differs from a blood smear of a healthy person
• the lymphocytes in a person with leukaemia, such as those shown in Fig. 6.1, differ from those of a healthy person.