AP Biology Campbell Active Reading Guide Chapter 12 – The Cell Cycle

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1. What are the three key roles of cell division? State each role, and give an example.

1. Reproduction – binary fission of bacterium into two individual organisms. 2. Growth and Development – sand dollar embryo cell division and development 3. Tissue Renewal – dividing bone marrow to create new RBCs

2. What is meant by the cell cycle?

The cell cycle describes the life of a cell from the time it is first formed to its own division into two daughter cells.

3. What is the meaning of genome?

A cell’s endowment of DNA.

4. How many chromosomes are in a human somatic cell?

46 chromosomes

5. Name two types of somatic cells in your body.

skin cells and liver cells

6. What is a gamete?

Reproductive cell

7. Name two types of gametes.

Human spermatozoa and ovum

8. How many chromosomes are present in a human gamete?

23

9. Define chromatin.

Chromatin is the entire complex of DNA and proteins that is the building material of chromosomes.

10. How many DNA molecules are in each of your somatic cells?

46

11. a) Define chromosome

a package of DNA molecules

11. b) Define chromatid

a copy of the original chromosome, joined with a sister chromatid

11. c) Define centromere

the region containing specific DNA sequences where a chromatid is attached to its sister

11. d) Define chromatin

the entire complex of DNA and proteins that is the building material of chromosomes

12. Summarize what occurs at the DNA level in each stage of diagram (not shown).

1. One condensed eukaryotic chromosome 2. Duplicated chromosome, consisting of two sister chromatids bound by sister chromatid cohesion. 3. Molecular and mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells.

13. What is mitosis? How is it different from cytokinesis?

Mitosis is the division of genetic information in the nucleus in the process of cell division, while cytokinesis is the division of the cytoplasm in the process of cell division.

14. What occurs in meiosis? How is the chromosome number of daughter cells different?

Meiosis yields nonidentical daughter cells that have only 1 set of chromosomes, half as many as the parent cell.

15. a). By what process are the damaged cells in a wound repaired? (Meiosis/Mitosis)

mitosis

15. b). By what process are eggs formed? (Meiosis/Mitosis)

meiosis

15. c). By what process does a zygote develop into a multicellular organism? (Meiosis/Mitosis)

mitosis

15. d). In what process are identical daughter cells produced? (Meiosis/Mitosis)

mitosis

15. e). Which process reduces the chromosome number of daughter cells? (Meiosis/Mitosis)

meiosis

16. a). A hedgehog has 90 chromosomes in its somatic cells. How many chromosomes did the hedgehog inherit from each parent?

45

16. b). A hedgehog has 90 chromosomes in its somatic cells. How many chromosomes are in each of the hedgehog’s gametes?

45

16. c). A hedgehog has 90 chromosomes in its somatic cells. How many chromosomes will be in each somatic cell of the hedgehog’s offspring?

90

17. Give a brief explanation of what happens in each phase of the cell cycle.

G₁ – first gap, the cell grows S – synthesis, the cell continues to grow and copies its chromosomes G₂ – second gap, cell continues growing and completes preparation for cell division M – mitosis and cytokinesis of the cell occur

18. What are the components of the mitotic spindle? What is the source of theses components?

It consist of fibers made from microtubules and associated proteins, which come from disassembled microtubules of the cytoskeleton.

19. What is another name for the centrosome?

Microtubule organizing center

20. Sketch and label a centrosome with two centrioles.

(Diagram not yet available)

21. What are the components of the mitotic spindle?

It consist of fibers made from microtubules and associated proteins.

22. Describe what happens to the centrosome during interphase and then prophase.

During interphase, a single centrosome duplicates, forming two centrosomes which remain together near the nucleus. In prophase, they grow apart as spindle microtubules grow out from them.

23. What is a kinetochore?

A kinetochore is a structure of proteins associated with specific sections of chromosomal DNA at each centromere.

24. a) Phase G₂ of interphase – What are important features of this phase?

– A nuclear envelope encloses the nucleus – Nucleus contains one or more nucleoli – Two centrosomes have formed by duplication of a single centrosome – Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed

24. b) Prophase – What are important feature of this phase?

– Chromatin fibers condense into discrete chromosomes – Nucleoli disappear – Each duplicated chromosome appears as two conjoined sister chromatids as two conjoined sister chromatids – Mitotic spindle forms – Centrosomes move away from each other

24. c) Prometaphase – What are some important features of this phase?

– The nuclear envelope fragments – The microtubules invade the nuclear area – Chromosomes become even more condensed – Each of the two chromatids of chromosomes have a kinetochore, or specialized protein – Some microtubules attach to kinetochores, jerking centrosomes back and forth – Nonkinetochore microtubules interact with those from the opposite pole of the spindle

24. d) Metaphase – What are some important features of this phase?

– The centrosomes are now at opposite poles of the cells – The chromosomes convene at the metaphase plate, which is equidistant from the two poles – For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite poles

24. e) Anaphase – What are some important features of this phase?

– Lasts only few minutes, shortest phase – Begins when cohesion proteins are cleaved – This allows sister chromatins to part and become centrosomes – The two daughter chromatins move toward opposite ends of cell as kinetochore microtubules shorten – The cell elongates as nonkinetochore microtubules lengthen

24. f) Telophase and Cytokinesis

– Two daughter nuclei form – Nuclear envelopes arise from portions of endomembrane system – Nucleoli reappear – Chromosomes become less condensed – Remaining spindle microtubules are depolymerized —————————————- – Division of cytoplasm creates two daughter cells by end of cytokinesis – In animal cells, cytokinesis occurs from cleavage furrow

25. Explain the difference between kinetochore and nonkinetochore microtubules. What is the function of each?

26. At which end do kinetochore microtubules shorten during anaphase? Explain the Inquiry Figure that supports where this shortening occurs.

The microtubules shorten from the kinetochore side. The University of Wisconsin discovered this by labeling microtubules with a yellow florescence dye, then tracking the movement of a region on the microtubules with a laser.

27. Describe cytokinesis in animal cells.

Daughter animal cells separate because of a contractile ring of actin microfilaments around the cytoplasm, which contacts and pinches cell in two when reacting with myosin molecules in the cell.

28. Describe cytokinesis in a plant cell.

During telophase, vesicles coalesce in the middle of the cell producing a cell plate. The plate enlarges until it fuses with the cell membrane and forms two daughter cells.

29. How is the cell plate formed? What is the source of material for the cell plate?

The cell plate is formed by a coalescence of vesicles carrying cell wall materials.

30. Describe binary fission.

A prokaryotic replicates its DNA, grows to about double its size, then pinches off into two daughter cells.

31. a) Describe the differences between prokaryotes and eukaryotes in mode of reproduction.

Prokaryotes reproduce by binary fission, while eukaryotes reproduce by mitosis.

31. b) Describe the differences between prokaryotes and eukaryotes in number of chromosomes.

Prokaryotes usually have one chromosome, while eukaryotes can have any number from the tens to the thousands.

31. c) Describe the shape of the bacterial chromosome in prokaryotes.

Bacterial chromosomes are circular, while eukaryotic chromosomes are linear.

32. What controls the cell cycle?

The cell cycle is driven by signalling molecules present in the cytoplasm

33. What is a cell cycle checkpoint?

A checkpoint in the cell cycle is a control point where "stop" and "go-ahead" signals can regulate the cycle.

34. Summarize what happens at each checkpoint.
G₁ –
G₂ –
M –

35. What is the G₀ Phase? Describe this phase.

A nondividing stage where a cell exits the cycle at a checkpoint until it receives a "go-ahead" signal at the G₁ checkpoint.

36. What is a protein kinase?

Protein kinases are enzymes that activate/deactivate other proteins by phosphorylating them.

37. Kinases drive the cell cycle, but they must be activated by the attachment of a _______

cyclin

38. The activity of cyclin-dependent kinases (CDks) rises and falls. Why?

The activity rises and falls based on changes in the concentration of its cyclin partner.

39. What does MPF trigger? What are some specific activities it triggers?

It triggers the cell’s passage past the G₂ checkpoint into M phase. It phosphorylates a variety of proteins, triggering mitosis, and acts as a direct/indirect kinase, which fragments the nuclear envelope and contributes to events required for spindle formation and chromosome condensation.

40. What happens if all the chromosome kinetochores are not attached to spindle fibers? When this occurs, which checkpoint is not passed?

Only when the kinetochores are all properly attached to the spindle does the appropriate regulatory protein complex become active. When this occurs, the M-phase checkpoint is not passed.

41. What are growth factors? How does platelet-derived growth factor (PDGF) stimulate fibroblast division?

Growth factors are proteins released by certain cells that stimulate other cells to divide. PDGFs bind to fibroblast receptor tyrosine kinases that allows cells to pass G₁ checkpoint and divide.

42. Explain each normal cell behavior that cancer cells no longer show.
1. Density-dependent inhibition –
2. Anchorage dependence –

1. A phenomenon in which crowded cells stop dividing. 2. Cells must be attached to a sub-stratum such as the inside of a culture jar or the ECM of a tissue.

43. What is the source of HeLa cells? How old are they? Note that, unlike normal cells, HeLa cells are immortal!

Henrietta Lacks, a female cancer patient. 66 years old.

44. What is transformation? What is metastasis?

The process that converts a normal cell to a cancer cell; The spread of cancer cells distant from their original site.

45. Distinguish between a benign tumor and a malignant tumor.

A benign tumor has too few genetic and cellular changes to survive at another site. A malignant tumor includes cells that can spread to new areas and impair organ function.

46. List at least two specific cancer treatments, and tell how each treatment works.

1. High energy radiation subjected to a localized tumor is more harmful to it than normal cells because the tumors have lost DNA repair mechanisms. 2. Chemotherapy is toxic to actively metastatic tumors.

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