Cell Cycle.pdf

ACT OF ENTRUSTMENT TO OUR LADY ASSUMED INTO HEAVEN O holy and glorious Virgin Mary, our Queen assumed into heaven, we cherish you with a special love, we place ourselves under your care our being, our families, our university, and our country....

ACT OF ENTRUSTMENT TO OUR LADY ASSUMED INTO HEAVEN O holy and glorious Virgin Mary, our Queen assumed into heaven, we cherish you with a special love, we place ourselves under your care our being, our families, our university, and our country. May we please you, O Queen and Mother, with zeal in prayer and patient perseverance in work and studies. Keep watch over us and turn your eyes full of mercy toward the whole world. Amen.  CELL CYCLE Lesson Objectives 3 1 Compare mitosis and Characterize the meiosis, and their phases of the cell role in the cell- cycle and their division cycle control points 4 2 Explain the Describe the stages of significance or mitosis/meiosis applications of mitosis/ meiosis  CELL CYCLE  01 OVERVIEW This lesson will enhance your understanding on one of the key features of life which is cell reproduction. This will provide you with the concepts on the different stages of cell cycle and the two types of cell division: mitosis and meiosis, and explain their significance on an organism.  Introduction The ability to reproduce in kind is a basic characteristic of all living things. Cells need to undergo cycles as part of their growth and to repair or replace damaged ones. Cell cycle enables an organism to continue its existence by multiplying itself in controlled and systematic processes. Cell Cycle The cell cycle is an ordered series of events involving cell growth and cell division that produces two new daughter cells. Cells on the path to cell division proceed through a series of precisely timed and carefully regulated stages of growth, DNA replication, and division that produces two identical (clone) cells.. Interphase During interphase, the cell undergoes normal growth processes while also preparing for cell division. In order for a cell to move from inter-phase into the mitotic phase, many internal and external conditions must be met. Interphase G1 phase First Gap- Cell Growth S phase DNA Synthesis G2 phase Second gap- Preparation for Mitosis G1 Phase During the G1 stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus.  In the S phase, DNA replication S Phase can proceed through the mechanisms that result in the formation of identical pairs of DNA molecules. Sister chromatids are firmly attached to the centromeric region. The centrosome is duplicated during the S phase.  The two centrosomes will give rise to the mitotic spindle, the S Phase apparatus that orchestrates the movement of chromosomes during mitosis. At the center of each animal cell, the centrosomes of animal cells are associated with a pair of rod-like objects, the centrioles, which are at right angles to each other. G2 Phase In the G2-phase, the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation. Some cell organelles are duplicated The final preparations for the mitotic phase must be completed before the cell is able to enter the first stage of mitosis. Mitotic Phase The mitotic phase is a multistep process during which the duplicated chromosomes are aligned, separated, and move to opposite poles of the cell, and then are divided into two new identical daughter cells. Mitosis Proper Prophase In prophase, the chromosomes condense and are now visible even with just using the ordinary light microscope. In the late part of prophase, the nuclear envelope and the nucleolus disappear. The kinetochore, a special protein complex, appears at the centromere. Metaphase Astral microtubules are those that grow only near the centrosome (the structure with the centrioles). Polar microtubules grow away from the centrosome. These overlap at the middle where the chromosomes are located, but they are still not attached to the kinetochore. Kinetochore microtubules are the only ones attached to the kinetochore.  In anaphase A, the kinetochore Anaphase microtubules of the spindle fibers separate and move the sister chromatids toward opposite poles. In anaphase B, the polar microtubules begin to elongate, while the astral microtubules pull them on the other side. These result in the poles moving farther apart from each other.  In telophase, the Telophase chromosomes uncoil, and both the nucleolus and the nuclear envelope reappear. Cytokinesis continues with the visible appearance of the cleavage furrow. Telophase A cell plate forms. Think about this! Why Mitosis is important?  Mitosis First, mitosis ensures that the number of chromosomes of the parent cell is identical to its two daughter cells. For example, humans have 46 chromosomes in each cell in the diploid state (2n). A diploid cell has two sets of chromosomes, each coming from the parent cell. So, if the parent cell has 46 chromosomes, then the two daughter cells resulting from mitosis will each have 46 chromosomes (2n) also.  Mitosis Mitosis also replaces the damaged cells in wounds.  Mitosis The growth of hair is also due to the mitotic activity of its root. Cancer patients undergoing chemotherapy may lose the mitotic activity in the hair root.  ACT OF ENTRUSTMENT TO OUR LADY ASSUMED INTO HEAVEN O holy and glorious Virgin Mary, our Queen assumed into heaven, we cherish you with a special love, we place ourselves under your care our being, our families, our university, and our country. May we please you, O Queen and Mother, with zeal in prayer and patient perseverance in work and studies. Keep watch over us and turn your eyes full of mercy toward the whole world. Amen.  CELL CYCLE Part II Lesson Objectives 1 3 Characterize the Compare mitosis and phases of the cell meiosis, and their cycle and their role in the cell- control points division cycle 2 4 Explain the significance Describe the stages of or applications of mitosis/ mitosis/meiosis meiosis Meiosis Meiosis reduces the number of chromosomes of the diploid cell into halves: one half for the sperm and the other half for the egg, turning them into haploid cells. Meiosis Two divisions: Meiosis I is called reductional division Meiosis II is called equational division Meiosis I Homologous Pairs Prophase I Leptotene Zygotene Pachytene Diplotene Diakinesis Prophase I In the leptotene stage, chromatins condense and chromosomes appear. In the zygotene stage, synapsis starts. In the pachytene stage, synapsis is complete. At this point, crossing-over can take place. This process increases genetic variations of the organism because different combinations of exchanged genetic materials are allowed to happen. Prophase I In the diplotene stage, the synaptonemal complex starts to dissolve, and the homologous chromosomes start to separate in a process called terminalization. In diakinesis, the homologous chromosomes continue to separate and the chiasmata undergo terminalization. Metaphase I Homologous chromosomes move to the metaphase plate or equatorial plate. Anaphase I The homologous chromosomes separate in anaphase I. Each chromosome still holds the sister chromatids. Telophase I At this stage, homologous chromosomes have reached the poles. The resulting cells have only half the number of chromosomes. Chromosomes still have pairs of attached chromatids. Meiosis II  Note that the following events will be similar to mitosis, except that the daughter cells produced will have only half of their parent's genetic material. Prophase II In this process, the chromosomes begin to condense again. The nuclear membrane and the nucleolus disappear. Spindle fibers begin to form. Metaphase II The chromosomes align at the equatorial plate. The kinetochores are then attached to the centromere of each sister chromatid. Anaphase II The sister chromatids begin to separate. Each sister chromatid moves to the opposite poles. This may have adverse effects depending on the chromosomes affected. Anaphase II In humans, when chromosome 21 experiences nondisjunction, the resulting consequence is a person with Down syndrome. Anaphase II These may result in Klinefelter syndrome or Turner syndrome. A person with Klinefelter syndrome has XXY as sex chromosomes. A person with Turner syndrome, on the other hand, has just one of the sex chromosome. Telophase II In telophase II, the chromosomes uncoil. The nuclear membrane and the nucleolus reappear. Gametogenesis  Meiosis The haploid sperm and egg produced in meiosis will meet during fertilization. Question?