Chapter 12 The Cell Cycle

Functions of Cell Division Fig. 12-2 Functions of Cell Division 100 µm 200 µm 20 µm (a) Reproduction (b) Growth and development (c) Tissue renewal Repair Figure 12.2 The functions of cell division Organisms develop from a single cell Single-celled eukaryote Repair/replace damaged cells

Continuity of Life is Based on Cell Division 2. 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

Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cell’s genome. A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 12-3 Figure 12.3 Eukaryotic chromosomes 20 µm

Gametes (n) have half as many chromosomes as somatic cells. Somatic cells (2n) (body cells) have two sets (pairs) of chromosomes. A total of 46. 5. Muscle, nerve. blood Gametes (n) have half as many chromosomes as somatic cells. reproductive cells: sperm and eggs 23 chromosomes in human gamete 9. 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

Distribution of Chromosomes During Eukaryotic Cell Division 11. chromosome- one DNA molecule and associated proteins Each duplicated chromosome has two identical sister chromatids, which separate during cell division. The centromere is the narrow “waist” of the duplicated chromosome, where the two chromatids are most closely attached. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

single DNA molecule 0.5 µm Chromosomes DNA molecules Chromo- some arm Fig. 12-4 0.5 µm Chromosomes DNA molecules single DNA molecule Chromo- some arm Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Figure 12.4 Chromosome duplication and distribution during cell division Separation of sister chromatids Centromere Sister chromatids

13. Mitosis, the division of the nucleus Cytokinesis, the division of the cytoplasm 14. Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

S (DNA synthesis) G1 Cytokinesis G2 Mitosis Fig. 12-5 INTERPHASE S (DNA synthesis) G1 Cytokinesis G2 Mitosis Figure 12.5 The cell cycle MITOTIC (M) PHASE

Phases of the Cell Cycle 17. The cell cycle consists of Mitotic (M) phase (mitosis and cytokinesis) Interphase: G1 normal cell growth S copying of chromosomes G2 growth in preparation for cell division. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

microtubule-organizing center Replicates during interphase. Move apart during prophase. 22. A structure of proteins associated with specific sections of chromosomal DNA at the centromere.

Centrosome Fig. 12-7 Aster Sister chromatids Microtubules Chromosomes Metaphase plate Kinetochores Centrosome 1 µm Figure 12.7 The mitotic spindle at metaphase Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm

Chromosome, consisting of two sister chromatids Fig. 12-6b G2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Nonkinetochore microtubules Figure 12.6 The mitotic division of an animal cell Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore Kinetochore microtubule

Telophase and Cytokinesis Fig. 12-6d Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Nucleolus forming Figure 12.6 The mitotic division of an animal cell Daughter chromosomes Nuclear envelope forming Spindle Centrosome at one spindle pole

Kinetochores help separate chromatids. Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cell, not attached to chromosomes. Kinetochores help separate chromatids. 26. As chromosomes moved poleward, the microtubule segments on kinetochore side shorten while those on spindle side stayed the same. For the Cell Biology Video Microtubules in Cell Division, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cytokinesis: A Closer Look 27. In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow in the plasma membrane. A contractile ring of actin microfilaments beneath the furrow contracts and deepens the furrow. In plant cells, a cell plate enlarges until its surrounding membrane fuses with the plasma membrane of a neighboring cell. Vesicles from Golgi apparatus move to the middle of the cell and coalesce to form cell plate. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 12-9 Cytokinesis Vesicles forming cell plate Wall of parent cell 1 µm 100 µm Cleavage furrow Cell plate New cell wall Figure 12.9 Cytokinesis in animal and plant cells Contractile ring of microfilaments Daughter cells Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

Binary Fission 30. In binary fission, the chromosome replicates (beginning at the origin of replication), and the two daughter chromosomes move apart as the cell elongates. Plasma membrane grows inward. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Binary Fission Cell wall Origin of replication Plasma membrane E. coli cell Bacterial chromosome Two copies of origin Origin Origin Figure 12.11 Bacterial cell division by binary fission

The Evolution of Mitosis Mode of reproduction: pro- binary fission, euk- mitosis Number of chromosomes: pro- 1, euk- many Shape of bacterial chromosome: pro- circular, euk- linear Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Concept 12.3: The eukaryotic cell cycle is regulated by a molecular control system 32. The concentration of certain cytoplasmic molecules controls cell cycle. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The Cell Cycle Control System 33. The clock has specific checkpoints where the cell cycle stops until a go-ahead signal is received Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint Fig. 12-14 G1 checkpoint Control system S G1 G2 M Figure 12.14 Mechanical analogy for the cell cycle control system M checkpoint G2 checkpoint

Controlled by degradation of cyclin. 34. G1- If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide. If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a nondividing state called the G0 phase. Controlled by degradation of cyclin. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

G0 G1 G1 G1 checkpoint (b) Cell does not receive a Fig. 12-15 G0 G1 checkpoint Figure 12.15 The G1 checkpoint G1 G1 Cell receives a go-ahead signal @ G1 checkpoint. (b) Cell does not receive a go-ahead signal --> exit.

G2- checks for DNA damage during synthesis controlled by accumulation of cyclins M- checks for problems in metaphase-anaphase transition, controlled by MPF G0- nondividing state most body cells are in this state, ex. nerve and liver

The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases Kinases must be activated by cyclins. Changes in concentration of cyclin partner. 39. MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(a) Fluctuation of MPF activity and cyclin concentration during Fig. 12-17a M G1 S G2 M G1 S G2 M G1 MPF activity Cyclin concentration Figure 12.17 Molecular control of the cell cycle at the G2 checkpoint Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle

Stop and Go Signs: Internal and External Signals at the Checkpoints 40. Kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase. M checkpoint is not passed. 41. Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide. PDGF molecules triggers a signal transduction pathway that allows cells to pass G1 checkpoint Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Scalpels Petri plate Without PDGF cells fail to divide With PDGF Fig. 12-18 Scalpels Petri plate Without PDGF cells fail to divide Figure 12.18 The effect of a growth factor on cell division With PDGF cells prolifer- ate Cultured fibroblasts 10 µm

External Signals 42. Besides growth factors, another example of external signals is density-dependent inhibition, in which crowded cells stop dividing Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Density-dependent inhibition Fig. 12-19 Anchorage dependence Density-dependent inhibition Density-dependent inhibition Figure 12.19 Density-dependent inhibition and anchorage dependence of cell division 25 µm 25 µm (a) Normal mammalian cells (b) Cancer cells

44. - 45. 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. If abnormal cells remain at the original site, the lump is called a benign tumor. Malignant tumors invade surrounding tissues and can 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

Cancer: Does NOT obey cell cycle control signals Lymph vessel Tumor Blood vessel Cancer cell Glandular tissue Metastatic tumor 1 A tumor grows from a single cancer cell. 2 Cancer cells invade neigh- boring tissue. 3 Cancer cells spread to other parts of the body. 4 Cancer cells may survive and establish a new tumor in another part of the body. Figure 12.20 The growth and metastasis of a malignant breast tumor

radiation- damages DNA in cancer cells chemotherapy drugs- interfere with specific steps of cell cycle

Various Cell Cycle Phases in onion root tip:

Fig. 12-UN3

Fig. 12-UN4

You should now be able to: Describe the structural organization of the prokaryotic genome and the eukaryotic genome. List the phases of the cell cycle; describe the sequence of events during each phase. List the phases of mitosis and describe the events characteristic of each phase. Draw or describe the mitotic spindle, including centrosomes, kinetochore microtubules, nonkinetochore microtubules, and asters. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Compare cytokinesis in animals and plants. Describe the process of binary fission in bacteria and explain how eukaryotic mitosis may have evolved from binary fission. Explain how the abnormal cell division of cancerous cells escapes normal cell cycle controls. Distinguish between benign, malignant, and metastatic tumors. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings