Scientists used cells called fibroblasts to study factors that cause nondividing cells in the G0 stage of the cell cycle to reen
ter the cell cycle and undergo mitosis. In a laboratory, fibroblasts typically grow and divide when they are cultured in a growth medium that contains 10% serum (the liquid part of blood that remains after blood clots). If fibroblasts are cultured for 48 hours in the absence of serum (serum-starvation), they stop dividing and enter the G0 stage of the cell cycle.
The scientists divided serum-starved fibroblasts into groups to which they added no serum, 10% serum, or 0.1% serum. Each of the groups with 0.1% serum was also treated to block the production of only one or combinations of four proteins (p16, p18, p21, and p27) that are inhibitors of cyclin-dependent kinases. The scientists grew the fibroblasts for 48 hours and then measured the amount of DNA replication taking place to determine whether the cells had reentered the cell cycle. The scientists compared each group of cells to the group cultured with 10% serum and plotted the data (Figure 1).
Figure 1. DNA replication by treated fibroblasts relative to DNA replication by fibroblasts cultured with 10% serum. The treatment of each group of cells is shown in the table directly under the graph. + means the protein is present; − means the protein is absent.
(a) Based on the data for the groups of cells cultured with 0.1% serum (groups 3 to 7), identify which of the four proteins tested do(does) not appear to play a role in blocking cell cycle entry by fibroblasts.
(b) Based on the data for the groups of cells cultured with 0.1% serum (groups 3 to 7), identify the groups(s) most likely to include cells undergoing mitosis.
(c) Neurons (nerve cells) of the central nervous system (brain and spinal cord) are in G0 of the cell cycle and generally do not divide in response to an injury. The scientists predict that they can use the data from this experiment to help them treat individuals who suffer from spinal cord injuries. Provide reasoning to support the scientists’ prediction.
The scientists divided serum-starved fibroblasts into groups to which they added no serum, 10% serum, or 0.1% serum. Each of the groups with 0.1% serum was also treated to block the production of only one or combinations of four proteins (p16, p18, p21, and p27) that are inhibitors of cyclin-dependent kinases. The scientists grew the fibroblasts for 48 hours and then measured the amount of DNA replication taking place to determine whether the cells had reentered the cell cycle. The scientists compared each group of cells to the group cultured with 10% serum and plotted the data (Figure 1).
Figure 1. DNA replication by treated fibroblasts relative to DNA replication by fibroblasts cultured with 10% serum. The treatment of each group of cells is shown in the table directly under the graph. + means the protein is present; − means the protein is absent.
(a) Based on the data for the groups of cells cultured with 0.1% serum (groups 3 to 7), identify which of the four proteins tested do(does) not appear to play a role in blocking cell cycle entry by fibroblasts.
(b) Based on the data for the groups of cells cultured with 0.1% serum (groups 3 to 7), identify the groups(s) most likely to include cells undergoing mitosis.
(c) Neurons (nerve cells) of the central nervous system (brain and spinal cord) are in G0 of the cell cycle and generally do not divide in response to an injury. The scientists predict that they can use the data from this experiment to help them treat individuals who suffer from spinal cord injuries. Provide reasoning to support the scientists’ prediction.
1 answer:
Answer:
a)
Based on the data for the group of cells, among the four proteins, protein p16 does not appear to play a role in blocking cell cycle entry by fibroblasts. The evidence for this is in group 7, where, in the absence of the other proteins the p16 presence has helped the replication of DNA almost as good as the growth in the 10% serum.
In the other groups (3 to 6) the presence of any other protein has always inhibited the DNA replication compared to the fibroblast in 10% serum.
b)
Groups 4 to 7 have higher chance of including cells undergoing mitosis as they are showing more DNA replication compared to the group 1 which has 0% serum. In this group since it has been cultured for 48 hours in the absence of serum (serum-starvation), they stop dividing and enter the G0 stage of the cell cycle.
c)
The data here would provide the crucial information on which protein is required to induce the cells to enter the cell cycle. To recover from an injury the cells should divide and repair the wound, this will happen through stimulating the cell with the required protein. It would also shed light on which protein would inhibit the cells from entry into the cell cycle.
Note: Figure is added in the attachment section
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