Transcript Cell Cycle
The Cell Cycle Created by: Fatima Olayan Mariam Faraj Hassan Ismail Laila Hammoud Start of the cycle • The cell cycle is the series of changes that a cell under goes from the time it forms until it divides. • Newly formed cells grow from a time then divides to form two new cells, which in turn may grow and divide. • While the cycle seems rather simple the phases and timing of the cell are quite complex. Interphase • Before a cell actively divides, it must grow and duplicate much of its contents, so that two “daughter” cells can form – Interphase • During interphase, the cell obtains nutrients, utilizes them to manufacture new living material, and maintains routine “housekeeping” functions. • Interphase is in phases- DNA is replicated during the S phase, which is bracketed by two gap periods, called G1 and G2, when other structures are duplicated. Cell Division • One type of cell division is meiosis, which is part of gametogenesis, the formation of egg cells and sperm cells. • Reduction division, a process of meiosis, makes sure an egg fertilized by a sperm must have 46 chromosomes and both egg and sperm must have their normal number of 23 chromosomes. • The other form of cell division increases cell number, which is necessary for growth and development and for wound healing. Cont. Cell Division • It consists of two separate processes: Division of the nucleus, which is mitosis and division of the cytoplasm called cytokinesis. • Sperm and egg cells and red blood cells are the only cells that cant be divided by mitosis. • The nucleus contains the DNA which means the division must be precise. • New cells coming from mitosis need to have complete inaccurate copy of information to live. • DNA is doubled in interphase but split in mitosis. Mitosis Phase: Prophase • When the chromosomes in the nucleus get stained and become visible it’s a sign that • • • • a cell is going to divide. Since the cell has been through S phase, each prophase chromosome is composed of two identical portions, which are temporarily attached to a region on each called the centromere. During prophase two new centriole pairs move to opposite ends of the cell. Nuclear envelope and nucleus break up, disperse, and are no longer visible. Spindle shaped array of microtubules forms between the centrioles as they move apart. Metaphase • The second stage of cell division, after prophase, during which the chromosomes become attached to the spindle fibers. • Chromosomes line up half way between the centrioles because of microtubule activity. • Spindle fibers attach to the centromeres of each chromosome so that a fiber from one pair of centrioles contacts one centromere, and a fiber from the other pair of centrioles attaches to the other centromere. Anaphase • The stage of meiotic or mitotic cell division in which the chromosomes move away from one another to opposite poles of the spindle. • The chromosomes that separated are moved by microtubule activity to. • The spindle fiber shortens and pull their attached chromosomes towards the centrioles at opposite ends of the cell. Telophase • Telophase, the last phase of mitosis, is when the chromosomes complete their migration toward the centrioles. • This phase is like the reverse of prophase, when the chromosomes start approaching the centrioles, they began to elongate and unwind from rodlike shapes into the threadlike fibers of chromatin. • Nuclear envelope forms around chromosome set and nucleoli appear in the new nuclei. • The last step is when the microtubules break into tubulin molecules. The Phases of Mitosis! Cytoplasmic Division • Cytoplasmic division starts in anaphase and is when the cell membrane starts to constrict down the middle of the cell. • This constriction is called cleavage furrow and continues through telophase. • The ring of microfilaments, attached to the inner surface of the cell membrane, divides the cytoplasm. • They put the chromosomes on opposite sides of the cell. • The ring separates the new formed nuclei and puts half o the organelles into each new cell. • The new cells have different sizes and number of organelles but still have the same genetic information Cell Differentiation • Cell division explains how fertilized egg develops into an individual consisting of trillions of cells, of at least 260 specialized types. • Stem cells are cells that retain the ability to divide repeatedly without specializing. • A stem cell divides mitotically to yield either two daughter cells like itself or one daughter cell that is a stem cell and one that becomes partially specialized, termed a progenitor cell. • Ability for a stem cell to divide and give rise to at least one other stem cell is called self renewal. Cell Death • Cells that don’t divide or specialize could actually die. • Apoptosis is a form of cell death that is a normal part of development, rather than having injuries or diseases. • Inside the fetus apoptosis carves away webbing between developing fingers and toes, removes extra brain cells, and preserves only those immune system cells that recognize the bodys cell surface. • Even after birth apoptosis occurs, when you get burnt it peels away the damaged skin cells that might cause cancer. Clinical Connections • In the process of transcytosis endocytosis and exocytosis become structurally and functionally linked. • In transcytosis, a particle enters by endocytosis, journeys through the cytoplasm and then exits the cell by exocytosis from the other end, transcytosis thereby escorts substances across single cell layers. EXIT TICKET!!!! •3 Things you learned •2 •1 Main ideas Question you have!!