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Making Inferences After nine population doublings, would the rate of cell division be different between the two cultures? After 15? Why?

Making Inferences After nine population doublings, would the rate of cell division be different between the two cultures? After 15? Why?

Human Anatomy & Physiology (11th Edition)
Human Anatomy & Physiology (11th Edition)
11th Edition
ISBN:9780134580999
Author:Elaine N. Marieb, Katja N. Hoehn
Publisher:Elaine N. Marieb, Katja N. Hoehn
Chapter1: The Human Body: An Orientation
Section: Chapter Questions
Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...
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Do question number 3 making inferences
Inquiry & Analysis Why Do Human Cells Age? Effect of Telomerase on Cell Culture Growth Population doublings Human cells appear to have built-in life spans. As you learned 30 60 90 120 150 in this chapter, cell biologist Leonard Hayflick reported in 1961 the startling result that skin cells growing in tissue culture, such as those growing in culture flasks in the photo below, will Normal Telomerase plus divide only a certain number of times. After about 50 population doublings, cell division stops (a doubling is a round of cell division producing two daughter cells for each dividing cell; for example, going from a population of 30 cells to 60 cells). If a cell sample is taken after 20 doublings and frozen, when thawed, it resumes growth for 30 more doublings and then stops. An explanation of the "Hayflick limit" was suggested in 1978, when researchers first glimpsed an extra length of DNA at the end of chromosomes. Dubbed telomeres, these lengths proved to be composed of the simple DNA sequence TTAGGG, 0 3 6 9 12 15 18 21 24 27 30 33 repeated nearly a thousand times. Importantly, telomeres Months TTAGGG TTAGGG TTAGGG TTAGGG TTAGGG--- were found to be substantially shorter in the cells of older body tissues. This led to the hypothesis that a run of some 16 TTAGGGS was where the DNA replicating enzyme, called polymerase, first sat down on the DNA (16 TTAGGGS being the size of the enzyme's "footprint"), and because of being its docking spot, the polymerase was unable to copy that bit. Thus, a 100-base portion of the telomere was lost by a chromosome during each doubling as DNA replicated. Eventually, after some 50 doubling cycles, each with a round of DNA replication, the telomere would be used up and there would be no place for the DNA replication enzyme to sit. The cell line would then enter senescence, no longer able to proliferate. This hypothesis was tested in 1998. Using genetic engineering, researchers transferred into newly established Courtesy Priv. Doz. Dr. Roland Zel human cell cultures a gene that leads to expression of an enzyme called telomerase that all cells possess but no body b. After how many doublings do the telomerase plus cell uses. This enzyme adds TTAGGG sequences back to the cells cease to divide in this experiment? end of telomeres, in effect rebuilding the lost portions of the telomere. Laboratory cultures of cell lines with (telomerase 3. Making Inferences After nine population doublings, would the rate of cell division be different between the plus) and without (normal) this gene were then monitored for two cultures? After 15? Why? many generations. The graph displays the results. 4. Drawing Conclusions How does the addition of the Analysis telomerase gene affect the senescence of skin cells growing in culture? Does this result confirm the telomerase 1. Applying Concepts a. Variable. In the graph, what is the dependent variable? b. Comparing Continuous Processes. How do normal skin cells (blue line) differ in their growth history from telomerase plus cells with the telomerase gene (red line)? hypothesis this experiment had set out to test? 5. Further Analysis a. Cancer cells are thought to possess mutations disabling the cell's ability to keep the telomerase gene shut off. How would you test this hypothesis? 2. Interpreting Data a. After how many doublings do the normal cells cease to divide? Is this consistent with the telomerase hypothesis? b. Sperm-producing cells continue to divide throughout a male's adult life. How might this be possible? How would you test this idea? Relative growth rate
Transcribed Image Text:Inquiry & Analysis Why Do Human Cells Age? Effect of Telomerase on Cell Culture Growth Population doublings Human cells appear to have built-in life spans. As you learned 30 60 90 120 150 in this chapter, cell biologist Leonard Hayflick reported in 1961 the startling result that skin cells growing in tissue culture, such as those growing in culture flasks in the photo below, will Normal Telomerase plus divide only a certain number of times. After about 50 population doublings, cell division stops (a doubling is a round of cell division producing two daughter cells for each dividing cell; for example, going from a population of 30 cells to 60 cells). If a cell sample is taken after 20 doublings and frozen, when thawed, it resumes growth for 30 more doublings and then stops. An explanation of the "Hayflick limit" was suggested in 1978, when researchers first glimpsed an extra length of DNA at the end of chromosomes. Dubbed telomeres, these lengths proved to be composed of the simple DNA sequence TTAGGG, 0 3 6 9 12 15 18 21 24 27 30 33 repeated nearly a thousand times. Importantly, telomeres Months TTAGGG TTAGGG TTAGGG TTAGGG TTAGGG--- were found to be substantially shorter in the cells of older body tissues. This led to the hypothesis that a run of some 16 TTAGGGS was where the DNA replicating enzyme, called polymerase, first sat down on the DNA (16 TTAGGGS being the size of the enzyme's "footprint"), and because of being its docking spot, the polymerase was unable to copy that bit. Thus, a 100-base portion of the telomere was lost by a chromosome during each doubling as DNA replicated. Eventually, after some 50 doubling cycles, each with a round of DNA replication, the telomere would be used up and there would be no place for the DNA replication enzyme to sit. The cell line would then enter senescence, no longer able to proliferate. This hypothesis was tested in 1998. Using genetic engineering, researchers transferred into newly established Courtesy Priv. Doz. Dr. Roland Zel human cell cultures a gene that leads to expression of an enzyme called telomerase that all cells possess but no body b. After how many doublings do the telomerase plus cell uses. This enzyme adds TTAGGG sequences back to the cells cease to divide in this experiment? end of telomeres, in effect rebuilding the lost portions of the telomere. Laboratory cultures of cell lines with (telomerase 3. Making Inferences After nine population doublings, would the rate of cell division be different between the plus) and without (normal) this gene were then monitored for two cultures? After 15? Why? many generations. The graph displays the results. 4. Drawing Conclusions How does the addition of the Analysis telomerase gene affect the senescence of skin cells growing in culture? Does this result confirm the telomerase 1. Applying Concepts a. Variable. In the graph, what is the dependent variable? b. Comparing Continuous Processes. How do normal skin cells (blue line) differ in their growth history from telomerase plus cells with the telomerase gene (red line)? hypothesis this experiment had set out to test? 5. Further Analysis a. Cancer cells are thought to possess mutations disabling the cell's ability to keep the telomerase gene shut off. How would you test this hypothesis? 2. Interpreting Data a. After how many doublings do the normal cells cease to divide? Is this consistent with the telomerase hypothesis? b. Sperm-producing cells continue to divide throughout a male's adult life. How might this be possible? How would you test this idea? Relative growth rate
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