Review the Concepts

1. What two properties define a stem cell? Distinguish between a totipotent stem cell, a pluripotent stem cell, and a precursor (progenitor) cell.

2. Where are stem cells located in plants? Where are stem cells located in adult animals? How does the concept of a stem cell differ between animal and plant systems?

3. In 1997, Dolly the sheep was cloned by a technique called somatic-cell nuclear transfer (or nuclear-transfer cloning). A nucleus from an adult mammary cell was transferred into an egg from which the nucleus had been removed. The egg was allowed to divide several times in culture, then the embryo was transferred to a surrogate mother who gave birth to Dolly. Dolly died in 2003 after mating and giving birth herself to viable offspring. What does the creation of Dolly tell us about the potential of nuclear material derived from a fully differentiated adult cell? Does the creation of Dolly tell us anything about the potential of an intact, fully differentiated adult cell?

4. Identify whether the following contain totipotent, pluripotent, or multipotent cells: (a) inner cell mass, (b) morula, (c) eight-cell embryo, (d) trophectoderm.

5. True or false: Differentiated somatic cells have the capacity to become reprogrammed to become other cell types. Provide one line of evidence discussed in the chapter that corroborates your response.

6. Explain how intestinal stem cells were first identified and then experimentally shown to be multipotent stem cells.

7. Explain how hematopoietic stem cells were experimentally shown to be both multipotent and capable of self-renewal.

8. The nematode C. elegans has proved to be a valuable model organism for studies of cell birth, cell asymmetry, and cell death. What properties of C. elegans render it so well suited for these studies? Why is so much information from C. elegans experiments of use to investigators interested in mammalian development?

9. Asymmetric cell division often relies on cytoskeletal elements to generate or maintain the asymmetric distribution of cellular factors. In S. cerevisiae, what factor is localized to the bud by myosin motors? In Drosophila neuroblasts, what factors are localized apically by microtubules?

10. Discuss the role of par genes in generating anterior/posterior polarity in the C. elegans embryo.

11. How do studies of brain development in knockout mice support the statement that apoptosis is a default pathway in neuronal cells?

12. Compare and contrast cell death by apoptosis and by necrosis.

13. Identify and list the functions of the three general classes of proteins that control cell death.

14. Based on your understanding of the events surrounding cell death, predict the effect(s) of the following on the ability of a cell to undergo apoptosis:

  1. Functional CED-9; nonfunctional CED-3

  2. Active Bax and cytochrome c; nonfunctional caspase-9

  3. Inactive PI-3 kinase; active Bad

15. TNF and Fas ligand bind cell-surface receptors to trigger cell death. Although the death signal is generated external to the cell, why do we consider the death induced by these molecules to be apoptotic rather than necrotic?

16. Predict the effects of the following mutations on the ability of a cell to undergo apoptosis:

  1. Mutation in Bad such that it cannot be phosphorylated by protein kinase B (PKB)

  2. Overexpression of Bcl-2

  3. Mutation in Bax such that it cannot form homodimers

One common characteristic of cancer cells is a loss of function in the apoptotic pathway. Which of the mutations listed above might you expect to find in some cancer cells?

17. How do IAPs (inhibitors of apoptosis proteins) interact with caspases to prevent apoptosis? How do mitochondrial proteins interact with IAPs to prevent inhibition of apoptosis?