Cell Cycle PDF

INTERPHASE AND M PHASE LG 6.1 Rudolf Virchow - applied the cell theory to explain the effects of diseases on the tissues and organs of the body - “Omnis cellula e cellula” Parent cells divide into daughter cells - Caused accidentally by foreign factors (bacteria, virus, and injuries)...

INTERPHASE AND M PHASE LG 6.1 Rudolf Virchow - applied the cell theory to explain the effects of diseases on the tissues and organs of the body - “Omnis cellula e cellula” Parent cells divide into daughter cells - Caused accidentally by foreign factors (bacteria, virus, and injuries) - May be programmed as a result of mutations or aging of cells Cell cycle - Ordered series of events that may lead to cell division and the production of 2 daughter cells (contains chromosomes identical to the parent cell) - For unicellular organisms, bacteria and yeast, produces new organisms (forms colonies in a short amout of time) Phases of the cell cycle - INTERPHASE -> M PHASE - G1 -> S -> G2 -> PROPHASE -> PROMETAPHASE -> METAPHASE -> ANAPHASE -> TELOPHASE -> CYTOKINESIS Interphase - The initial stage of the cell cycle - 90% of the cell cycle - G1 (4-5 hours) : interval between the M phase and the DNA replication (aka S Phase) : in this phase, the cell is active (grows physically larger, copies the organlles, and makes molecular building blocks) but the DNA wasn’t replicated yet : for nondividing cells, they will proceed to a G0 stage (do not grow and multiply) - S phase (10-12 hours) : DNA synthesis or replication : each parent chromosome must be duplicated once (forms two side-by-side units called sister chromatids) : Centrosome (present in only animals cells and plays a key role in division) : if the conditions aren’t met, then the cell cannot normally progress to the next phases  - G2 phase (4-6 hours) : for further cellular growth : the cell is roughly doubled : DNA is replicated, 2 centrosomes were formed : nuclear envelope encloses the nucleus and its contents are reorganized M Phase - Caused by Mitosis (the nucleus divides wherein it’s the separation of the daughter chromosomes) Prophase (spindle apparatus) - over half of the duration of mitosis - centrioles in the centrosomes will start to migrate towards the opposing poles of the cell while the mitotic spindle assembles between the two centrosomes - the nucleolus begins disintegrating - sister chromatids are held together at the centromere along their length by a protein complex called cohesion Prometaphase - The chromosome movement towards the midline region of the cell, perpendicular to the axis od the spindle fibers (the nuclear envelope breaks down while the chromosomes become shorter and thicker) - Each chromatid has a kinetochore (origin of the spindle fibers) Metaphase - The chromosome configuration (migration of the chromosomes into metaphase plate) - The sister chromatid pairs come to lie in the equatorial plane of the cell where each entromere aligned at the metaphase plate with the chromosome arms extending outward - The microtubules form the centrosome region that are the opposite polls of the cell referred to as kinetochore microtubules are attached to the kinetochore of each sister chromatid Anaphase - Shortest stage of mitosis - The sister chromatids will separate (pulled towards the spindle pole to which they are attached) (loosens the centromere) - Shorter kinetochore microtubules Telophase - Final stage of mitosis - The 2 sets of chromatids arrive at the pole at the spindle and the pulling-apart process ceases - New nuclear envelope - Each daughter cell inherits one pair of sister chromatids (decondensed or uncoil) - Mitosis or nuclear division is now complete producing two identical nuclei Cytokinesis - The last stage in the cell cycle - Cytoplasmic division - Begins during the late anaphase and is mostly complete by the end of the telophase - Varies in different organisms (plant cells: cell plate -> middle lamella; animal cells: contractile ring -> cleavage furrow) Mitotic index - [(number of cells in a specific sphase in mitosis)/(total numbre of cells)] * 100