Download Mitosis Phases of mitosis Early prophase and more Study Guides, Projects, Research Cell Biology in PDF only on Docsity!
Mitosis
Mitosis is a type of cell division in which one cell (the mother ) divides to produce two new cells (the daughters ) that are genetically identical to itself. In the context of the cell cycle, mitosis is the part of the division process in which the DNA of the cell's nucleus is split into two equal sets of chromosomes.
Phases of mitosis
Mitosis consists of four basic phases: prophase, metaphase, anaphase, and telophase. These phases occur in a sequence order, and cytokinesis - the process of dividing the cell contents to make two new cells - starts in anaphase or telophase.
Early prophase
The mitotic spindle starts to form, the chromosomes start to condense, and the nucleolus disappears.
- In early prophase , the cell starts to break down some structures and build others up, setting the stage for division of the chromosomes.
- The chromosomes start to condense (making them easier to pull apart later on).
- The mitotic spindle begins to form. The spindle is a structure made of microtubules, strong fibers that are part of the cell’s “skeleton.” Its job is to organize the chromosomes and move them around during mitosis.
- The spindle grows between the centrosomes as they move apart.
- The nucleolus (or nucleoli, plural), a part of the nucleus where ribosomes are made, disappears.
Late prophase (prometaphase). The nuclear envelope breaks down and the chromosomes are fully condensed. In late prophase (sometimes also called prometaphase ), the mitotic spindle begins to capture and organize the chromosomes.
- The chromosomes finish condensing, so they are very compact.
- The nuclear envelope breaks down, releasing the chromosomes.
- The mitotic spindle grows more, and some of the microtubules start to “capture” chromosomes.
Chromosomes line up at the metaphase plate, under tension from the mitotic spindle. The two sister chromatids of each chromosome are captured by microtubules from opposite spindle poles. In metaphase , the spindle has captured all the chromosomes and lined them up at the middle of the cell, ready to divide.
- All the chromosomes align at the metaphase plate
- At this stage, the two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles.
Cytokinesis in animal and plant cells.
Cytokinesis , the division of the cytoplasm to form two new cells, overlaps with the final stages of mitosis. It may start in either anaphase or telophase, depending on the cell, and finishes shortly after telophase.
Cytokinesis in an animal cell: an actin ring around the middle of the cell pinches inward, creating an indentation called the cleavage furrow. Cytokinesis in a plant cell: the cell plate forms down the middle of the cell, creating a new wall that partitions it in two.
In animal cells, cytokinesis is contractile, pinching the cell in two like a coin purse with a drawstring. The “drawstring” is a band of filaments made of a protein called actin, and the pinch crease is known as the cleavage furrow. Plant cells can’t be divided like this because they have a cell wall and are too stiff. Instead, a structure called the cell plate forms down the middle of the cell, splitting it into two daughter cells separated by a new wall.
