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Chapter 12: The Cell Cycle. The student is responsible for: All bold faced words in the chapter. Being able to describe the stages of mitosis, Figure 12.5. Lectures will emphasize “The Regulation of the Cell Cycle” pgs 224 – 229. Figure 12.1a The functions of cell division: Reproduction.
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Chapter 12: The Cell Cycle • The student is responsible for: • All bold faced words in the chapter. • Being able to describe the stages of mitosis, Figure 12.5. Lectures will emphasize “The Regulation of the Cell Cycle” pgs 224 – 229.
Figure 12.1a The functions of cell division: Reproduction Reproduction of an amoeba
Figure 12.1c The functions of cell division: Tissue renewal Reproduction of bone marrow cells.
Figure 12.2 Eukaryotic chromosomes Kangaroo rat cells
Figure 12.3 Chromosome duplication and distribution during mitosis
Figure 12.4 The cell cycle Organelles and proteins are made Organelles and proteins are made
Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase
Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis.
Mitotic Spindle and Its Relationship to Chromosomes Mitotic spindle is composed of microtubules MTs emerge from the centrosome The centrosome is an organelle but has no membrane Centrosome replicates at the beginning of mitosis and each will end at one of the poles of the nucleus. Spindle attaches at the kinetochore, a region on the sister chromatids. Spindles from both ends of the nucleus attach to the kinetochores on each sister chromatid and through pulling and tugging align the chromosomes in the middle or metaphase plate
Figure 12.7 Testing a hypothesis for chromosome migration during anaphase In order to move the chromosomes to the poles, the kinetochores need to shorten. Are they shortening near the centrosome or the kinetochore? After the microtubules were labeled with a laser, it was found that the MTs nearest the chromosome or kinetochore shortened.
Figure 12.10 Bacterial cell division (binary fission) (Layer 3)
Regulation of the Cell Cycle • A molecular control system drives the cell cycle • Specific chemical signals in the cytoplasm regulation the cell cycle. • This was shown by fusing cells in different stages of the cell cycle and the cell not as advanced moved into the more advanced stage as if something from the cytoplasm of the advanced cell caused a stimulation. • This was called a Cell Cycle Control System
Regulation of the Cell Cycle cont’d • Cell Cycle Checkpoints • “Go” Checkpoints: is there enough protein, organelles, etc. • G1 Checkpoint • Most important in mammalian cells • Once past the G1 checkpoint, cell will complete the cell cycle • With no “go” signal, it remains in a nondividing state. • Some cells, liver cells, can transition from nondividing to dividing . • Other cells, muscle or nerve cells, remain in nondividing state.
Figure 12.13 Mechanical analogy for the cell cycle control system
Regulation of the Cell Cycle cont’d • The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases • Kinases will phosphorylate proteins which can either activate them or inactivate them. • Kinase + cyclin is an active kinase so it is a cyclin-dependent kinase or CdK. • M Phase Promoting Factor or MPF is a complex of a kinase and cyclin. • MPF triggers movement of the cell cycle out of G2 and into mitosis • MPF will cause the phosphorylation of many proteins and these phosphorylated proteins can activate cellular processes. i.e., breakdown of the nuclear membrane. • MPF decomposes and inactivates itself.
Figure 12.14 Molecular control of the cell cycle at the G2 checkpoint
Internal and External Cues • Internal Signals: Messages from the Kinetochores • Anaphase is delayed until all the chromosomes are lined up properly and attached to the kinetochores. • If all the kinetochores are not attached to the microtubules then cell will not go into anaphase.
Internal and External Cues (cont’d) • External Signals: Growth Factors • Platelet Derived Growth Factor or PDGF • Platelets in the blood stream have receptors for this growth factor and when the receptors are bound to the PDGF, cell division is stimulated. • This happens in petri dishes as well as within your body. • Density-Dependent Inhibition • Anchorage dependence
Cancer Cells have escaped controls of the cell cycle • Tumor • Benign Tumor: if abnormal cells remain in original site. • Malignant Tumor • Metastasis
Figure 12.17 The growth and metastasis of a malignant breast tumor
