Transcript Mitosis
The Cell Cycle Chapter 12 Mitosis Cell division Produce 2 daughter cells Same genetic information Mitosis Asexual reproduction Growth Repair Genome Genetic information Prokayotes Nucleoid Circular DNA No nucleus Genome Eukaryotes Chromosomes: DNA Associated proteins Chromatin: Complex of DNA & proteins Makes up chromosomes Humans 46 chromosomes Dogs 78 chromosomes Eukaryotes Somatic cells: Body cells 46 chromosomes Gametes: Sex cells Sperm & eggs 23 chromosomes Eukaryotes Chromatid: Duplicated chromosome Centromere: Attachment to another chromatid Prior to cell division chromosomes replicates Fig. 12-4 0.5 µm Chromosomes Chromosome arm DNA molecules Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Separation of sister chromatids Centromere Sister chromatids Fig. 12-5 G1 S (DNA synthesis) G2 Cell cycle Cell cycle: Events that occur to produce two cells 1. Interphase (G1, S, G2) 2. Mitosis 3. Cytokinesis Interphase Growth phase of the cell G1, S, G2 Interphase Where most of cycle is spent Rate of division depends on job of cell. Liver cells may divide rapidly Mature muscle cells do not divide at all Few cells will be in mitosis at a time Most are in interphase Interphase G1 or Gap 1 phase Cell is doing its job Preparing for the S phase. Chromosomes are single Can last weeks to years or happen very quickly Interphase S phase DNA replication happens 2 sister chromatids G2 or Gap 2 phase cell prepares for division Mitochondria & other organelles replicate Microtubules begin to form Chromosomes condense Interphase Mitosis Nucleus & its contents divide Distributed equally Forming two daughter cells Prophase, metaphase, anaphase and telophase Prophase Beginning of mitosis Chromosomes continues to condense Mitotic spindle forms Begins to move chromosomes to center Nuclear membrane disintegrates Nucleolus disappears Prophase Metaphase Chromosomes line up in center of cell Centromeres become aligned along the cells center Metaphase Anaphase Microtubules shorten Separates the sister chromatids Chromosomes move towards the poles Anaphase Telophase Chromosomes are at the poles Nuclear envelope reforms Nucleolus reappears Chromosomes uncoil or de-condense Telophase Cytokinesis Cytoplasm separates Animal cells: cleavage furrow pinches the cells in two Plant cells: cell plate is formed between the cells Grows until a new cell wall is formed Cytokinesis Fig. 12-9 100 µm Cleavage furrow Contractile ring of microfilaments Vesicles forming cell plate Wall of parent cell Cell plate 1 µm New cell wall Daughter cells (a) Cleavage of an animal cell (SEM) Daughter cells (b) Cell plate formation in a plant cell (TEM) Binary fission Prokaryotes produce 2 daughter cells by binary fission Binary fission 1. Replication of the DNA Origin of replication: Specific location on the DNA 2. Two DNA molecules move to the ends of the cell 3. Septation Formation of a new cell membrane & a septum. Binary fission 4. Septum begins to grow inward 5. Cell pinches into two cells. Cell cycle control system Check points Control point with stop & go signals G1, G2 and M phases Fig. 12-14 G1 checkpoint Control system G1 M G2 M checkpoint G2 checkpoint S Cell cycle control system Special proteins Protein kinases & cyclins Cdks – cycle dependent kinases MPF-cyclin-Cdk complex “M-phase promoting factor” Regulate if cell stops or proceeds in the cycle Fig. 12-17b Degraded cyclin G2 Cdk checkpoint Cyclin is degraded MPF Cyclin (b) Molecular mechanisms that help regulate the cell cycle Cyclin accumulation Cdk Figure 12.16a M G1 S G2 M MPF activity G1 S G2 M Cyclin concentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle G1 Cell cycle control system Go-ahead signal at G1 Divides No signal G0 phase Does not divide Figure 12.17 G1 checkpoint G0 G1 G1 Without go-ahead signal, cell enters G0. G1 S M With go-ahead signal, cell continues cell cycle. (a) G1 checkpoint G2 G1 G1 M G2 M G2 M checkpoint Anaphase Prometaphase Without full chromosome attachment, stop signal is received. (b) M checkpoint G2 checkpoint Metaphase With full chromosome attachment, go-ahead signal is received. Cell cycle control system Receives signals The environment Other cells Growth factors Density-dependent inhibition Anchorage dependence Tumor Abnormal growth of cells Malfunction in control system Abnormal cells grow uncontrollably Benign: Non-cancerous growth Tumor Malignant: Cancerous growth Metastasis: Spread of cancer to distant locations p53 Protein Works at a checkpoint at G1 p53 determines if DNA is damaged If so stimulates enzymes to fix it Cell division continues Unable to repair damage Cell suicide occurs p53 Helps keep damaged cells from dividing Cancer cells p53 is absent or damaged p53 protein is found on the p53 gene Considered a tumor-suppressor gene Cigarette smoking causes mutations in this gene Henrietta Lacks 1951 developed cervical cancer Before cancer treatment Cells were removed First cells to grow in vitro Outside of the body Cell line is now known as HeLa cell line Helped in biomedical research