Cellular processes

Source: Wikipedia. Pages: 64. Chapters: Cell cycle, Meiosis, Cell division, Exocytosis, Endocytosis, Necrosis, Chromosomal crossover, Cellular differentiation, Genetic recombination, DNA repair, Biochemical switches in the cell cycle, Cell growth, Site-specific recombination, Autophagy, Septins, Cell migration, Endoplasmic Reticulum Associated Protein Degradation, Intraflagellar transport, Cap formation, Endocytic cycle, Parasexual cycle, Axon terminal, Phagocytosis, CDK7 pathway, Dynamin, Stringent response, Passive transport, Secretory pathway, Receptor-mediated endocytosis, Efferocytosis, Autolysis, Endoexocytosis, Formins, Nemosis, Coagulative necrosis, Necrobiology, Dentinogenesis, Trans-endocytosis, Bulk endocytosis, Afterhyperpolarization, Autophagin, Pinocytosis, Cytoplasmic streaming, Rap6, Pyknosis, Mitotic crossover, Invagination, Karyolysis, Autophagy database, Density-dependent inhibition, Potocytosis, Transcytosis, Histone methylation, Leptotene stage, Meiome, Necrobiosis, Non-specific, adsorptive pinocytosis, Filamentation, Karyorrhexis, Residual body, Branch migration, Fungating lesion, S phase index, Synizesis, Ectopic recombination, Interkinesis. Excerpt: DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as UV light and radiation can cause DNA damage, resulting in as many as 1 million individual molecular lesions per cell per day. Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe the gene that the affected DNA encodes. Other lesions induce potentially harmful mutations in the cell's genome, which affect the survival of its daughter cells after it undergoes mitosis. As a consequence, the DNA repair process is constantly active as it responds to damage in the DNA structure. When normal repair processes fail, and when cellular apoptosis does not occur, irreparable DNA damage may occur, including double-strand breaks and DNA crosslinkages. The rate of DNA repair is dependent on many factors, including the cell type, the age of the cell, and the extracellular environment. A cell that has accumulated a large amount of DNA damage, or one that no longer effectively repairs damage incurred to its DNA, can enter one of three possible states: The DNA repair ability of a cell is vital to the integrity of its genome and thus to its normal functioning and that of the organism. Many genes that were initially shown to influence life span have turned out to be involved in DNA damage repair and protection. Failure to correct molecular lesions in cells that form gametes can introduce mutations into the genomes of the offspring and thus influence the rate of evolution. DNA damage, due to environmental factors and normal metabolic processes inside the cell, occurs at a rate of 1,000 to 1,000,000 molecular lesions per cell per day. While this constitutes only 0.000165% of the human genome's approximately 6 billion bases (3 billion base pairs), unrepaired lesions in critical genes (such as tumor sup