Chapter 12

1. Chapter 12 The Cell Cycle

2. Concept 12.1: • Cell division results in genetically identical daughter cells • Cells duplicate their genetic material • Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

3. Cellular Organization of the Genetic Material • A cell’s endowment of DNA, its genetic information • Is called its

4. Figure 12.3 50 µm The DNA molecules in a cell • Are packaged into

5. Eukaryotic chromosomes • Consist of , a complex of DNA and protein that condenses during cell division • In animals • have two sets of chromosomes • have one set of chromosomes

6. Distribution of Chromosomes During Cell Division • In preparation for cell division • DNA is replicated and the chromosomes condense

7. 0.5 µm A eukaryotic cell has multiplechromosomes, one of which is represented here. Before duplication, each chromosomehas a single DNA molecule. Chromosomeduplication(including DNA synthesis) Once duplicated, a chromosomeconsists of two sister chromatidsconnected at the centromere. Eachchromatid contains a copy of the DNA molecule. Centromere Sisterchromatids Separation of sister chromatids Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Centromeres Sister chromatids Each duplicated chromosome • Has two which separate during cell division Figure 12.4

8. Eukaryotic cell division consists of • the division of the nucleus • , the division of the cytoplasm

9. INTERPHASE S(DNA synthesis) G1 CytokinesisMitosis G2 MITOTIC(M) PHASE Figure 12.5 Concept 12.2: Phases of the Cell Cycle • The cell cycle consists of • The

10. G2 OF INTERPHASE PROMETAPHASE PROPHASE Centrosomes(with centriole pairs) Aster Fragmentsof nuclearenvelope Early mitoticspindle Kinetochore Chromatin(duplicated) Centromere Nonkinetochoremicrotubules Kinetochore microtubule Chromosome, consistingof two sister chromatids Nuclearenvelope Plasmamembrane Nucleolus Figure 12.6 Mitosis consists of five phases • Prometaphase

11. METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Metaphaseplate Cleavagefurrow Nucleolusforming Nuclear envelopeforming Daughter chromosomes Centrosome at one spindle pole Spindle Figure 12.6

12. The Mitotic Spindle: • The mitotic spindle • Is an apparatus of that controls chromosome movement during mitosis • The spindle arises from the • And includes spindle microtubules and asters

13. Aster Centrosome MetaphasePlate Sisterchromatids Kinetochores Overlappingnonkinetochoremicrotubules Kinetochores microtubules 0.5 µm Microtubules Chromosomes Centrosome 1 µm Some spindle microtubules • attach to the of chromosomes and move the chromosomes to the Figure 12.7

14. Kinetochore Spindlepole In anaphase, sister chromatids separate • and move along the kinetochore microtubules toward opposite ends of the cell Figure 12.8

15. Nonkinetechore microtubules from opposite poles • Overlap and push against each other, elongating the cell • In telophase • Genetically identical daughter nuclei form at opposite ends of the cell

16. Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells Figure 12.9 A (a) Cleavage of an animal cell (SEM) Cytokinesis: • In animal cells • Cytokinesis occurs by a process known as cleavage, forming a

17. Vesiclesforming cell plate Wall of parent cell 1 µm Cell plate New cell wall Daughter cells (b) Cell plate formation in a plant cell (SEM) In plant cells, during cytokinesis Vesicles containing cell wall components migrate toward the center, coalesce, and form the new cell wall Figure 12.9 B

18. Prokaryotes • reproduce by a type of cell division called • The bacterial chromosome replicates • The two daughter chromosomes move apart • Plasma membrane “pinches” inward forming two new daughter cells

19. Concept 12.3: • The cell cycle is regulated by a molecular control system • The frequency of cell division varies with the type of cell • These cell cycle differences result from regulation at the molecular level

20. G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint The sequential events of the cell cycle • are directed by a distinct cell cycle control system, which is similar to a clock Figure 12.14

21. G0 G1 checkpoint G1 G1 (a) If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues      on in the cell cycle. (b) If a cell does not receive a go-ahead signal at the G1checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state. The clock has specific checkpoints • where the cell cycle stops until a go-ahead signal is received Figure 12.15 A, B

22. The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases • Two types of regulatory proteins are involved in cell cycle control • and (Cdks)

23. G1 G1 M G2 G2 S S M M (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle MPF activity Cyclin Time (b) Molecular mechanisms that help regulate the cell cycle 1 Synthesis of cyclin begins in late S phase and continues through G2. Because cyclin is protected from degradation during this stage, it accumulates. 5 During G1, conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled. G1 S Cdk M G2 DegradedCyclin G2checkpoint 2 Accumulated cyclin molecules combine with recycled Cdk mol- ecules, producing enough molecules of MPF to pass the G2 checkpoint and initiate the events of mitosis. Cdk Cyclin is degraded Cyclin MPF 4 During anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G1 phase. 3 MPF promotes mitosis by phosphorylating various proteins. MPF‘s activity peaks during metaphase. Figure 12.16 A, B The activity of cyclins and Cdks • fluctuates during the cell cycle

24. Stop and Go Signs: Internal and External Signals at the Checkpoints • Both intracellular and extracellular signals • Control the cell cycle checkpoints

25. Intracellular Signal • Sister chromatids at the metaphase plate will not separate unless all are attached to • Why is this important?

26. Extracellular Signal • stimulate other cells to divide • i.e. platelet derived growth factor (PDGF) • stimulates fibroblast division

27. (a) Normal mammalian cells. The availability of nutrients, growth factors, and a substratum for attachment limits cell density to a single layer. Cells anchor to dish surface and divide (anchorage dependence). When cells have formed a complete single layer, they stop dividing (density-dependent inhibition). If some cells are scraped away, the remaining cells divide to fill the gap and then stop (density-dependent inhibition). Figure 12.18 A 25 µm • Most animal cells exhibit in which they must be attached to a substratum to divide • In crowded cells stop dividing

28. Cancer cells do not exhibitanchorage dependence or density-dependent inhibition. Cancer cells. Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells. (b) Figure 12.18 B 25 µm Cancer cells • Exhibit neither density-dependent inhibition nor anchorage dependence

29. Loss of Cell Cycle Controls in Cancer Cells • Cancer cells • Do not respond normally to the body’s control mechanisms • Form tumors

30. 4 3 2 1 Lymphvessel Tumor Bloodvessel Glandular tissue Cancer cell MetastaticTumor A small percentage of cancer cells may survive and establish a new tumor in another part of the body. Cancer cells spread through lymph and blood vessels to other parts of the body. A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Cancer • tumors invade surrounding tissues and can • exporting cancer cells to other parts of the body where they may form secondary tumors Figure 12.19