Cell Cycle PDF

Cell Cycle Cell cycle, cell death and renewal CELL CYCLE Cell cycle - series of events that occur in the cell to prepare it for division into two daughter cells. There are 2 main stages in the cell cycle: interphase - the longest stage in which the cell increases its size and replicates its g...

Cell Cycle Cell cycle, cell death and renewal CELL CYCLE Cell cycle - series of events that occur in the cell to prepare it for division into two daughter cells. There are 2 main stages in the cell cycle: interphase - the longest stage in which the cell increases its size and replicates its genetic material; mitosis - stage during which there is cell division and distribution of genetic material between the two daughter cells that are identical to the mother cell.  INTERPHASE It is divided into three phases: - Phase G1: first stage of the cell cycle. Mitosis It is a period of cellular growth, where the cell regains its size after mitosis. The nucleolus is restored, there is synthesis of RNA, enzymes and (Gap 2) regulatory proteins necessary for all cell functions. (Gap 1) - Phase S: stage of DNA synthesis during the cell cycle. The cell (DNA synthesis) duplicates its DNA content. - Phase G2: synthesis of RNA and proteins necessary for cell division. Interphase  MITOSIS It is the process in which the cell divides giving rise to two identical daughter cells. First the nucleus is divided (cariokinesis) and then the cytoplasm is divided in two (cytokinesis). stem cell (diploid) 2c R 2c daughter cells (diploids) R 2c R STAGES: PROPHASE METAPHASE ANAPHASE TELOPHASE  MEIOSIS Meiosis is a special type of cell division that gives rise to gametes (ovules and sperm) The number of chromosomes is reduced from 2n to n - each gamete carries half the number of chromosomes so that, at fertilization, the zygote has the diploid number (2n) typical of the species. Gene recombination occurs during meiosis, generating genetic variability and diversity. Two consecutive divisions take place during meiosis that result in the formation of gametes n 2n n 2n  Mitosis vs. Meiosis https://youtu.be/jjEcHra3484  CELL DEATH The cell cycle can be interrupted by various factors that cause the death of the cell. These factors can be injuries or accidents, attack of pathogens, absence of vascular supply, or even by genetic programming. There are two mechanisms by which cells may die: Apoptosis: programmed cell death. It is a physiological process that happens, for example in: – cells that are genetically programmed from the embryonic stage for their destruction so that the organism can develop properly. – cells that must die to establish a balance with cell proliferation. – when intracellular damage occurs and the intervention of the immune system or an inflammatory reaction is not appropriate. Ex: Physical agents (radiation), chemical agents (toxics), tumour cells. Necrosis: process that occurs due to attacks or traumatic injuries. This process is not regulated and may damage the organism.  APOPTOSIS Modification of the cell shape and Macrophages decrease in cell size → loss of contact Normal with other cells Condensation of the cytoplasm (↓ volume) No changes in the organelles Apoptotic Condensation and fragmentation of Bodies nuclear chromatin (pyknosis) Fragmentation of the cell: fragments surrounded by PM - apoptotic bodies The cell membrane is not destroyed The apoptotic bodies are rapidly phagocytized Pyknosis There is no inflammatory reaction Embrionic development There are cells that during the embryonic development are genetically programmed to undergo apoptosis: cells that would form membranes between the fingers and toes, cells that would give rise to the formation of the tail in humans.  Maintaining body homeostasis Participates in the continuous remodeling and maturation of all organs and tissues. It helps maintain the balance between proliferation and cell death. Basal membrane Basal cells Activated Caspase 3 (apoptosis) Mammary duct Apoptosis Proliferation  NECROSIS Increase of cell size (the cell swells) Normal Reversible process at the beginning Mitochondrial damage Breakage of the cell membrane Release of the content to the extracellular medium Minimum modifications in the core Dissolution of the organelles Neighboring cells also submitted to this process There is an inflammatory reaction Tissue damage  Apoptosis Necrosis Macrophages Normal Normal Apoptotic Bodies Pyknosis