Transcript cell cycle
CELL CYCLE CHAPTER 12 Figure 12.0 Mitosis Figure 12.1a The functions of cell division: Reproduction Figure 12.1b The functions of cell division: Growth and development Figure 12.1c The functions of cell division: Tissue renewal Figure 12.2 Eukaryotic chomosomes Vocabulary Chromatin – long, thin fibers of DNA wrapped around proteins Chromosome – one long DNA molecule; condensed and clearly visible during cell division Chromatid – two identical DNA molecules attached by a centromere (sister chromatids) NEW VOCABULARY Centrosome – microtubule organizing center which includes a pair of centrioles Centrosomes replicate in interphase and move to opposite poles in prophase Centromere – region where 2 chromatids are attached to one another Kinetochore – specialized region of centromere where spindle fibers attach Figure 12.3 Chromosome duplication and distribution during mitosis CELL CYCLE Interphase G1 (first gap – cell grows) S (DNA synthesis = chromosomes replicate) G2 (second gap – cell grows) Mitosis Prophase Metaphase Anaphase Telophase Cell Cycle Animation Mitosis Animation Figure 12.4 The cell cycle Prophase Chromosomes visible Centrosomes move towards opposite poles and begin making spindle fiber Nuclear membrane, nucleus, and nucleolus disintegrate Spindle fiber form and some attach to the kinetochores of the centromeres Metaphase Chromosomes line up at the middle of the cell Figure 12.6 The mitotic spindle at metaphase Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase Anaphase Sister chromatids are pulled apart and move toward opposite ends of the cell by the spindle fiber Nonkinetochore spindle help elongate the cell Cell plate begins to form in plant cells (immature cell wall) Telophase Events are opposite those of prophase Nuclear membranes, nuclei, and nucleoli form in each new cell Cytokinesis occurs – (cleavage forms) Chromosomes unravel and become chromatin again Spindle fibers disintegrate Figure 12.5 The stages of mitotic cell division in an animal cell: metaphase; anaphase; telophase and cytokinesis. Figure 12.5x Mitosis Figure 12.8 Cytokinesis in animal and plant cells Figure 12.9 Mitosis in a plant cell Figure 12-09x Mitosis in an onion root BINARY FISSION Bacteria only have one chromosome so steps of mitosis are not needed Bacteria replicate via binary fission DNA replicates at a specific point (origin of replication) Figure 12.10 Bacterial cell division (binary fission) (Layer 3) Evolution of Mitosis Prokaryotic and eukaryotic cell division share some similar proteins that are involved in cell division Possible intermediates: Current examples in some protists Nuclear envelopes remain intact and replicated chromosomes attach to envelope As nucleus elongates, chromosome separate Spindle forms inside nucleus REGULATION OF CELL CYCLE Checkpoint – critical point in cell cycle where process can stop or go ahead according to signals Kinases – enzymes that can activate or inactivate something via phosphorylation Figure 12.13 Mechanical analogy for the cell cycle control system Restriction point – the most critical of checkpoints During G1, if signaled to proceed then cell usually completes cell cycle and divides If no signal to proceed, cell goes into nondividing state, G0 Most cells are in G0 Go signal means enter S and replicate DNA Cyclin is a protein that activates kinases that are called cyclin-dependent kinases or Cdks MPF (maturation promoting factor) – combination of Cdks and cyclin Cyclins accumulate during G2 and associate with Cdk’s to make MPF MPF initiates mitosis at G2 checkpoint by phosphorylating various proteins Nuclear membrane is phosphorylated and this causes it to break down Proteolytic enzymes break down MPF which helps end mitosis Figure 12.14 Molecular control of the cell cycle at the G2 checkpoint M Phase Checkpoint M phase (metaphase checkpoint) Kinetochores not attached yet to spindle send delay signals to prevent anaphase from starting too early. Why must the cell wait for all of the chromosomes to line up in the middle of metaphase before proceeding to anaphase? OTHER SIGNALS A signal that delays anaphase so that right number of chromosomes end up in each new cell Growth factors – external signals that can stimulate cell division Density-dependent inhibition – cells stop dividing when crowded Anchorage-dependent – most animal cells must be attach to substratum Figure 12.16 Density-dependent inhibition of cell division CANCER Cancer – cells that divide excessively and invade other tissues Metastasis – spread of cancer cells Tumor – mass of abnormal cells Benign – cells stay “put”, not cancer Malignant – cells move (metastasis), cancer Figure 12.17 The growth and metastasis of a malignant breast tumor Figure 12-17x1 Breast cancer cell Figure 12-17x2 Mammogram: normal (left) and cancerous (right)