Cell cycle and Mitosis

Cell Cycle http://www.le.ac.uk/ge/genie/vgec/sc/cellcycle.html

Cell Cycle Living cells go through a series of stages known as the cell cycle. The cells grow, copy their chromosomes, and then divide to form new cells. G1 phase. The cell grows. S phase. The cell makes copies of its chromosomes. Each chromosome now consists of two sister chromatids. G2 phase. The cell checks the duplicated chromosomes and gets ready to divide. www.le.ac.uk/ge/genie/vgec/images/cellcycle.png

Cell Cycle M phase. The cell separates the copied chromosomes to form two full sets (mitosis) and the cell divides into two new cells (cytokinesis). The period between cell divisions is known as 'interphase'. Cells that are not dividing leave the cell cycle and stay in G0. www.le.ac.uk/ge/genie/vgec/images/cellcycle.png

Mitosis Your body contains trillions of cells (thousands of millions). But you started life as a single cell - a fertilised egg cell. This cell then divided and divided to make more cells through a process called mitosis. Mitosis is a way of making more cells that are genetically the same as the parent cell. It plays an important part in the development of embryos, and it is important for the growth and development of our bodies as well. Mitosis produces new cells, and replaces cells that are old, lost or damaged. In mitosis a cell divides to form two identical daughter cells. It is important that the daughter cells have a copy of every chromosome, so the process involves copying the chromosomes first and then carefully separating the copies to give each new cell a full set. http://www.le.ac.uk/ge/genie/vgec/sc/cellcycle.html

Formation of Sister Chromatids Before mitosis, the chromosomes are copied. They then coil up, and each chromosome looks like a letter X in the nucleus of the cell. The chromosomes now consist of two sister chromatids. Mitosis separates these chromatids, so that each new cell has a copy of every chromosome. www.le.ac.uk/ge/genie/vgec/images/cellcycle.png http://www.le.ac.uk/ge/genie/vgec/sc/cellcycle.html

Cell Cycle and Mitosis www.le.ac.uk/ge/genie/vgec/images/cellcycle.png

MITOSIS Follow the link to enter an interactive presentation on MITOSIS http://www.johnkyrk.com/mitosis.html

Interphase The cell is engaged in metabolic activity and performing its prepare for mitosis (the next four phases that lead up to and include nuclear division). Chromosomes are not clearly discerned in the nucleus, although a dark spot called the nucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of which are organizational sites for microtubules.

Prophase Chromatin in the nucleus begins to condense and becomes visible in the light microscope as chromosomes. The nucleolus disappears. Centrioles begin moving to opposite ends of the cell and fibers extend from the centromeres. Some fibers cross the cell to form the mitotic spindle.

Prometaphase The nuclear membrane dissolves, marking the beginning of prometaphase. Proteins attach to the centromeres creating the kinetochores. Microtubules attach at the kinetochores and the chromosomes begin moving.

Metaphase Spindle fibers align the chromosomes along the middle of the cell nucleus. This line is referred to as the metaphase plate. This organization helps to ensure that in the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome.

Anaphase The paired chromosomes separate at the kinetochores and move to opposite sides of the cell. Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.

Telophase Chromatids arrive at opposite poles of cell, and new membranes form around the daughter nuclei. The chromosomes disperse and are no longer visible under the light microscope. The spindle fibers disperse, and cytokinesis or the partitioning of the cell may also begin during this stage.

Cytokinesis In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus. In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.

YouTube Video: Mitosis This video explains what happens during the different stages of mitosis http://www.youtube.com/watch?v=VlN7K1-9QB0 http://www.youtube.com/watch?v=VlN7K1-9QB0