1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 12 The Cell Cycle

2. Overview: The Key Roles of Cell Division The continuity of life is based on the reproduction of cells, or cell division In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for: – Development from a fertilized cell – Growth – Repair Cell division is an integral part of the cell cycle, the life of a cell from formation to its own division Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. Concept 12.1: Cell division results in genetically identical daughter cells Mitosis = Most cell division results in somatic cells (nonreproductive cells) - two sets of chromosomes with identical genetic information, DNA Meiosis = A special type of division produces nonidentical daughter cells (gametes; reproductive cells; sperm and egg cells) and have half as many chromosomes as somatic cells Genome - all the DNA in a cell – can consist of a single DNA molecule (common in prokaryotic cells) – number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

4. Fig. 12-4 0.5 µm Chromosomes Chromosome duplication (including DNA synthesis) Chromo- some arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids

5. Phases of the Cell Cycle The cell cycle consists of – Mitotic (M) phase – mitosis (division of the nucleus) and cytokinesis ( division of the cytoplasm ) – Interphase (cell growth and copying of chromosomes in preparation for cell division) Interphase (about 90% of the cell cycle) can be divided into subphases: – G 1 phase (“first gap”) – S phase (“synthesis”) – G 2 phase (“second gap”) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

6. Fig. 12-5 S (DNA synthesis) MITOTIC (M) PHASE Mitosis Cytokinesis G1G1 G2G2

7. Fig. 12-6 G 2 of Interphase Centrosomes (with centriole pairs) Chromatin (duplicated) Nucleolus Nuclear envelope Plasma membrane Early mitotic spindle Aster Centromere Chromosome, consisting of two sister chromatids Prophase Prometaphase Fragments of nuclear envelope Nonkinetochore microtubules Kinetochore microtubule Metaphase plate Spindle Centrosome at one spindle pole Anaphase Daughter chromosomes Telophase and Cytokinesis Cleavage furrow Nucleolus forming Nuclear envelope forming

8. Sister chromatids Aster Metaphase plate Centrosome Kineto- chores Kinetochore microtubules Overlapping nonkinetochore microtubules 0.5 µm Mitotic spindle - (apparatus of microtubules that controls chromosome movement) include: Centrosome - microtubule organizing center spindle microtubules Asters - radial array of short microtubules that extends from each centrosome Kinetochores - some spindle microtubules attach to chromosomes and move them Nonkinetochores push against each other elongating the cell Metaphase plate - midway point between the spindle’s two poles

9. Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM)(b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell Cell plate Daughter cells New cell wall 1 µm In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow. In plant cells, a cell plate forms during cytokinesis

10. Fig. 12-11-4 Origin of replication Two copies of origin E. coli cell Bacterial chromosome Plasma membrane Cell wall Origin Prokaryotes (bacteria and archaea) reproduce by cell division called binary fission Chromosomes replicate (beginning at the origin of replication), and the two daughter chromosomes move apart

11. Fig. 12-12 (a) Bacteria Bacterial chromosome Chromosomes Microtubules Intact nuclear envelope (b) Dinoflagellates Kinetochore microtubule Intact nuclear envelope (c) Diatoms and yeasts Kinetochore microtubule Fragments of nuclear envelope (d) Most eukaryotes Since prokaryotes evolved before eukaryotes, mitosis probably evolved from binary fission Certain protists exhibit types of cell division that seem intermediate between binary fission and mitosis The Evolution of Mitosis

12. Fig. 12-14 S G1G1 M checkpoint G2G2 M Control system G 1 checkpoint G 2 checkpoint Cell cycle control system is similar to a clock regulated by both internal and external controls

13. Fig. 12-15 G1G1 G0G0 G 1 checkpoint (a)Cell receives a go-ahead signal G1G1 (b) Cell does not receive a go-ahead signal G 0 phase - a nondividing state

14. The Cell Cycle Clock: Cyclins & Cyclin-Dependent Kinases Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin- dependent kinases (Cdks) The activity of cyclins and Cdks fluctuates during the cell cycle MPF (maturation-promoting factor) is a cyclin- Cdk complex that triggers a cell’s passage past the G 2 checkpoint into the M phase Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

15. Fig. 12-17 M G1G1 S G2G2 M G1G1 SG2G2 M G1G1 MPF activity Cyclin concentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle Degraded cyclin Cdk G1G1 S G2G2 M G2G2 checkpoint Cyclin is degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle Cyclin accumulation

16. Stop and Go Signs: Internal and External Signals at the Checkpoints Internal signal examples – kinetochores not attached to spindle microtubules send a signal that delays anaphase Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

17. Fig. 12-18 Petri plate Scalpels Cultured fibroblasts Without PDGF cells fail to divide With PDGF cells prolifer- ate 10 µm

18. Fig. 12-19 Anchorage dependence Density-dependent inhibition (a) Normal mammalian cells (b) Cancer cells 25 µm Density-dependent inhibition - crowded cells stop dividing Anchorage dependence (found in most animals) - must be attached to a substratum in order to divide

19. Loss of Cell Cycle Controls in Cancer Cells Cancer cells exhibit neither density- dependent inhibition nor anchorage dependence Cancer cells do not respond normally to the body’s control mechanisms Cancer cells may not need growth factors to grow and divide: – They may make their own growth factor – They may convey a growth factor’s signal without the presence of the growth factor – They may have an abnormal cell cycle control system Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

20. A normal cell is converted to a cancerous cell by a process called transformation Cancer cells form tumors- masses of abnormal cells within otherwise normal tissue – at the original site = benign tumor – Malignant tumors = invade surrounding tissues Metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

21. Fig. 12-20 Tumor A tumor grows from a single cancer cell. Glandular tissue Lymph vessel Blood vessel Metastatic tumor Cancer cell Cancer cells invade neigh- boring tissue. Cancer cells spread to other parts of the body. Cancer cells may survive and establish a new tumor in another part of the body. 1 2 3 4