Cell Cycle and Mitosis

Cell Reproduction Cell division is the process by which new cells are produced from one cell. Cell division results in two cells that are identical to the original parent cell.

Cell Cycle The cell cycle is a sequence of growth and division of a cell. The majority of a cell’s life is spent in the growth period known as interphase. Following interphase, a cell enters its period of nuclear division called mitosis. Following mitosis, the cytoplasm divides separating into two daughter cells. DNA synthesis and replication (S) Centrioles replicate (G2) Rapid growth and metabolic activity. (G2) (M)

Cell Cycle There are three stages in the cell cycle: 1.Interphase (G1, S, G2) 2. Mitosis (PMAT) 3. Cytokinesis DNA synthesis and replication (S) Centrioles replicate (G2) Rapid growth and metabolic activity. (G1) (M)

Stage 1: Interphase: A Busy Time Interphase, the busiest phase of the cell cycle, is divided into three parts. Rapid growth and metabolic activity. DNA synthesis and replication Centrioles replicate and cell prepares for division Each chromosome makes a copy, and the two resulting chromosomes are joined at the centromere.

Interphase: A Busy Time 1. During the first part, the cell prepares for division. 2. In the next part of interphase, the cell copies its DNA. 3. After the chromosomes have been duplicated, the cell enters another shorter growth period in which mitochondria and other organelles are manufactured and centrioles needed for cell division are assembled.

Stage 2: Mitosis is the process of nuclear division (cell nucleus and its contents) Mitosis consists of four phases: Prophase Metaphase Anaphase Telophase

Prophase: The First Phase of Mitosis During prophase, the chromatin coils to form visible chromosomes. The two halves of the doubled structure are called sister chromatids. Sister chromatids are held together by a structure called a centromere, which plays a role in chromosome movement during mitosis. centrioles begin to move to the poles, spindle fibers extend and the nuclear membrane disintegrates.

Prophase: The First Phase of Mitosis Centromere Sister Chromatids

Metaphase: The Second Stage of Mitosis During metaphase, the chromosomes move to the equator of the spindle. spindle fibers attach to chromosomes at the centromere and push them to the middle of the cell.

Anaphase: The Third Stage of Mitosis During Anaphase, the centromeres split and the sister chromatids are pulled apart to opposite poles of the cell.

Telophase: the Fourth Stage of Mitosis During Telophase, two distinct daughter cells are formed. The cells separate as the cell cycle proceeds into the next interphase.

In a Nut Shell

Cytokinesis Follwing telophase, the cell’s cytoplasm divides in a process called cytokinesis. Cytokinesis differs between plants and animals. Towards the end of telophase in animal cells, the plasma membrane pinches in along the equator. Animal cells: a cleavage furrow forming down the middle. Plant cells have a rigid cell wall, so the plasma membrane does not pinch in. A structure known as the cell plate is laid down across the cell’s equator. A cell membrane forms around each cell and new cell walls form on each side of the cell plate until separation is complete.

Results of Mitosis When mitosis is complete, unicellular organisms remain as single cells. In multicellular organisms, cell growth and reproduction result in groups of cells that work together as tissues to perform a specific function. Tissues organize in various combinations to form organs that perform more complex roles within the organism. Multiple organs that work together form an organ system.

Let’s Review

Now you’ve learned how new cells form from pre-existing cells. See if you can identify the different stages of mitosis in the following slide of onion cells undergoing nuclear division.

Onion cells in various stages of mitosis: