Cell Cycle Lecture 10 PDF

Chapter 12: The Cell Cycle Lecture Objectives ✓Know your Cell Types ✓Know the Types of Division ✓DNA (again) ✓Understand Chromosomes ✓Cell Cycle & the Controls on Cell Cycle ✓Mitosis & its phases ✓Cytokinesis Properties of Life Order Reproduction Growth and development Energy pr...

Chapter 12: The Cell Cycle Lecture Objectives ✓Know your Cell Types ✓Know the Types of Division ✓DNA (again) ✓Understand Chromosomes ✓Cell Cycle & the Controls on Cell Cycle ✓Mitosis & its phases ✓Cytokinesis Properties of Life Order Reproduction Growth and development Energy processing Regulation Response to the environment Evolutionary adaptation  Functions of Cell Division The continuity of life is based on the reproduction of cells= cell division  Cell Types Somatic Cells (nonreproductive) Gametes (reproductive) All cells start here in the Cell Cycle Cells have left Cell Cycle “Body cells” (Multi-cellular Eukaryotes) Sex Cells (reproductive cells) 2 sets= Diploid(in humans): 2n 1 set= Haploid: 1n contains full set of genetic contains half of the genetic complement complement In humans, 23 pairs of homologous In humans, either egg or sperm cell chromosomes Cellular Organization of the Genetic Material DNA molecules in a cell are packaged into chromosomes carry several hundred to a few thousand genes  Cellular Division Mitosis Meiosis Almost all Cellular Most cells never Division is Mitosis undergo Meiosis Results in 2 identical Results in 4 unique diploid somatic cells haploid gametes can be used in No longer in Cell Cycle reproductive binary fission (for single Occurs only in gonads celled organisms)  Cellular Division Mitosis Meiosis Almost all Cellular Most cells never Division is Mitosis undergo Meiosis Results in 2 identical Results in 4 unique diploid somatic cells haploid gametes can be used in No longer in Cell Cycle reproductive binary fission (for single Occurs only in gonads celled organisms)  Chromosomes Genome -All the DNA in a cell Packaged into Chromosomes 2 States: Chromatin= a complex of DNA and protein that condenses during cell division During division DNA is replicated & chromosomes condense Eukaryotic Chromosomes DNA in a chromosome is packed into an elaborate, multilevel system of coiling and folding. Histones are proteins used to package DNA in eukaryotes. Nucleosomes consist of DNA wound around several histone molecules.  Duplicating Chromosomes Before cell division the DNA of each chromosome is copied through the process of DNA replication & new histone protein molecules attach as needed. Results in 2 copies= sister chromatids, which contain identical genes. are joined together tightly at a narrow “waist” called the centromere.  Duplicating Chromosomes Before cell division the DNA of each chromosome is copied through the process of DNA replication & new histone protein molecules attach as needed. Results in 2 copies= sister chromatids, which contain identical genes. are joined together tightly at a narrow “waist” called the centromere. After division Once separated each chromatid: is considered a full-fledged chromosome & is identical to the original chromosome.  Cell Cycle Ordered sequence of events that extends from the time the cell is first formed to its own division Interphase (cell growth and copying of chromosomes in preparation for cell division) G1 phase (“first gap”) S phase (“synthesis”) G2 phase (“second gap”) Mitotic (M) phase (mitosis& cytokinesis) Interphase= G1, S phase, G2 & G0  5 Stages of Mitosis: Mnemonic Interphase– “I” Mitotic Phase the division of the genetic material in the nucleus Consists of 5 Phases 1. Prophase– “Politely” 2. Prometaphase– “Picked” 3. Metaphase– “My” 4. Anaphase– “Apples” 5. Telophase– “Today” Cytokinesis– “Cheers!” is the division of cytoplasm overlaps with the latter phases of mitotic phase “I politely picked my apples today, CHEERS!” Microtubule Polymerization Microtubules in Anaphase  The Mitotic Spindle structure made of microtubules that controls chromosome movement during mitotic phase of cell cycle In animal cell assembly of spindle microtubules begins in the centrosome The centrosome replicates during interphase, forms two centrosomes that migrate to opposite ends of the cell during prophase & prometaphase Microtubules attach to the kinetochore  At which end do kinetochore microtubules shorten during anaphase? Data from G. J. Gorbsky, P. J. Sammak, and G. G. Borisy, Chromosomes move poleward in anaphase along stationary microtubules that coordinately disassemble from their kinetochore ends, Journal of Cell Biology 104:9–18 (1987)  Mitosis Video https://www.youtube.com/watch?v=ofjyw7ARP1c Mitosis in a plant cell Cytokinesis- the final divide Animal cells- Cleavage Plant cells- Cell plate Animal Plant Cytokinesis - Animal Cells Cytokinesis - Plant Cells Mitosis: as a Mode of Reproduction: Binary Fission  Regulating the cell cycle Cell Cycle Control System The frequency of cell division varies with the type of cell differences result from regulation at the molecular level driven by chemical signals in cytoplasm Has distinct checkpoints to regulate Mechanical G1 checkpoint analogy for the cell cycle control system Control system S G1 M G2 M checkpoint G2 checkpoint Two G checkpoint 1 important G 0 checkpoints G1 G1 Without go-ahead signal, With go-ahead signal, cell enters G0. cell continues cell cycle. G1 S (a) G1 checkpoint M G2 G1 G1 M G2 M G2 M checkpoint G2 Anaphase checkpoint Prometaphase Metaphase Without full chromosome With full chromosome attachment, stop signal is attachment, go-ahead signal received. is received. (b) M checkpoint  Cell Cycle Control There are two types of regulatory protein involved in control: Cyclins proteins whose levels fluctuate cyclically Cyclin-dependent kinases (Cdks) enzymes that activate or inactivate other proteins by phosphorylating them MPF (maturation-promoting factor) is a cyclin- Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase Molecular control of the cell cycle at the G2 checkpoint  The effect of platelet derived growth factor (PDGF) on cell division Internal & External Signals at Checkpoints External physical factors may also effect cell division: Anchorage dependence—to divide, cells must be attached to a substratum Density-dependent inhibition, crowded cells will stop dividing  Density- dependent Inhibition & Anchorage Dependence of Cell Division Loss of Cell Cycle Controls in Cancer Cells Cancer cells manage to escape the usual controls on the cell cycle may not need growth factors to grow & divide because they: make their own growth factor convey a growth factor’s signal without the presence of the growth factor have an abnormal cell cycle control system  Cancer Cells A normal cell is converted to a cancerous cell by a process called transformation Cancer cells that are not eliminated by the immune system form tumors Benign tumors remain only at the original site Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body The growth and metastasis of a malignant breast tumor  Cancer Treatment 3 main types of cancer treatment: 1. Surgery to remove a tumor is usually the first step. 2. Radiation therapy, parts of the body that have cancerous tumors are exposed to high-energy radiation, which harms cancer cells more than normal cells. Is often effective against malignant tumors that have not yet spread. 3. Chemotherapy, the use of drugs to disrupt cell division, is used to treat tumors that have spread throughout the body.  Frontiers of Cancer Treatment One promising area is immunotherapy, treatments that use the body’s immune system to attack tumors. Immunotherapy can be done by boosting the body’s natural immunity in general or by boosting specific immune components that attack cancer cells. immune components may be created in the lab and injected into a patient. Many cancer researchers believe that immunotherapy represents the next major breakthrough in cancer treatment.  Cancer Prevention & Survival There are certain lifestyle changes you can make to reduce your chances of developing cancer or increase your chances of surviving it. These include not smoking, exercising adequately, avoiding overexposure to the sun, eating a high-fiber, low-fat diet, performing self-exams, and regularly visiting a doctor to identify tumors early. Lecture Objectives ✓Know your Cell Types ✓Know the Types of Division ✓DNA (again) ✓Understand Chromosomes ✓Cell Cycle & the Controls on Cell Cycle ✓Mitosis & its phases ✓Cytokinesis