EUKARYOTE CELL DIVISION: MITOSIS AND MEIOSIS
Division of Eukaryote cells involves a series of steps that are different from the process that Prokaryote cells go through to divide, a process called BINARY FISSION.
Cell division is more complicated in Eukaryote cells. The cells are larger and more complex.
The material must be distributed evenly and each daughter cell must have a new nuclear membrane.
Cell division may occur by either mitosis or meiosis, depending on what type of cell is involved.
All one cell organisms reproduce by mitosis.
Mitosis is used by multicellular organisms for growth and repair of all its cells, except sex cell or GAMATES.
The division of Eukaryote cells into daughter cells occurs in 2 stages:
– 1. The nuclear contents are divided by mitosis or meiosis, a process called KARYOKINESIS.
– 2. The cell division of the rest of the cell, a process called CYTOKINESIS.
Mitosis is the process where the genetic material of the cell is equally divided into 2 complete cells.
Mitosis is divided into 4 stages; PROPHASE, METAPHRASE, ANAPHASE and TELOPHASE.
– Prophase is the longest stage of Mitosis.
– For cell division to occur, the already replicated chromosome must be pulled apart.
– The chromosome that was doubled during S phase of Interphase, begins to coil, thicken and shorten, in order to be more easily moved during the process of cell division.
– A chromosome at Prophase becomes “X” shaped. It consists of joined CHROMITIDS, which are the doubled DNA structures from the S phase of Interphase.
– The structure that joins the chromatids is called a CENTROMERE.
– While the chromosomes are recoiling (pulling apart), the nucleoli and nuclear membrane are disappearing.
– At the same time spindles are forming that will help to align and move the chromosomes.
– The CENTRIOLES being to move to opposite ends of the cell.
– The centrioles line-up long, thin, wire-like structures called SPINDLE FIBERS across the length of the cell. (These spindle fibers will help line-up the chromosomes during the next phase of mitosis, Metaphase).
– The chromosomes move toward the middle of the cell.
– By the end of Prophase the nuclear membrane is broken down.
– In Meta phase the doubled chromosomes line up at the center of the cell.
– The centromeres divide in two.
– Metaphase last only as long as the chromosomes remain lined-up along the center of the cell.
– In Anaphase the 2 complete sets of chromosomes being to move toward opposite corners (poles) of the cell.
– Each chromosome appears to be dragged along by its centromere, which is attached to a spindle fiber.
– The division of the cytoplasm, or CYTOKINESIS, begins at the end of Anaphase.
– Telophase is the last stage of mitosis.
– The chromosomes reach their respective sides (poles) of the cell. While this is occurring the cell’s plasma membrane pinches in from both sides, enclosing the chromosomes, creating two separate cells.
– The chromosomes then uncoil and the nucleus reappears.
Mitosis ends when the new daughter cells go their separate ways.