The Biology Project > Cell Biology >
Intro. to Cell Cycle & Mitosis > Tutorial Mitosis What is (and is not) mitosis? Mitosis is nuclear division plus cytokinesis, and produces two identical daughter cells during prophase, prometaphase, metaphase, anaphase, and
telophase. Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell cycle. Interphase & mitosis
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.
| Mitosis
animation
(480 k)
| OR
|
Mitosis animation
Flash
|
|
Previous | Next Vocabulary The Biology Project
> Cell Biology > Intro. to Cell Cycle & Mitosis > Tutorial
http://www.biology.arizona.edu
All
contents copyright © 1997 - 2004. All rights reserved.
Meiosis: Advanced Look --> 1.) Meiosis I Meiosis is a key process of sexual reproduction. Meiosis I is the first cell division event in meiosis. During this phase the chromosomes in the diploid cell synapse, undergo recombination, and are finally separated into two new haploid daughter cells. Clicking on each of the thumbnail images will bring up
a larger, labeled version of the described scene. To see the Flash movie for the following sequence of images, click here.
|
| Before meiosis begins, the diploid germline cell goes through the three stages of interphase: G1, S, and G2. The DNA in the cell is replicated during the S, or Synthesis, stage.
| |
| Meiosis is divided into two phases, beginning with Meiosis I. The first stage of Meiosis I is prophase I. During the beginning of this stage, the chromosomes condense.
| |
| During the middle of prophase I, homologous chromosome undergo synapsis, or pairing up. This is followed by an exhange of DNA between non-sister chromatids. This exchange is called recombination, or crossing over.
| |
| At the end of prophase I, the nuclear membrane breaks down, the centrosomes have migrated to the opposite ends of the cell, and the spindle apparatus is being formed.
| |
| This is followed by metaphase I. During this stage, the spindle fibers, or microtubules, attach to the centromere of each chromosome. The chromosomes are then aligned at the equator, or mephase plate, of the cell.
| |
| Next is anaphase I. Here the homologous chromosome are pulled apart to opposite ends of the cell. It is important to note that the sister chromatids remain attached at the centromere of each chromosome.
| |
| The last stage of Meiosis I is telophase I. In telophase I, the microtubules break down, the nuclear membrane reforms, and the chromosomes return to an uncondensed state. The cell then divides into two haploid daughter cells by cytokinesis.
|
NEXT --> 2.) MEIOSIS II
During what phase does the nucleus disappear and DNA condense into chromosomes?
Metaphase
Metaphase is a stage during the process of cell division (mitosis or meiosis). Normally, individual chromosomes are spread out in the cell nucleus. During metaphase, the nucleus dissolves and the cell's chromosomes condense and move together, aligning in the center of the dividing cell.
What phase does chromosomes begin to condense?
Prophase. Mitosis begins with prophase, during which chromosomes recruit condensin and begin to undergo a condensation process that will continue until metaphase. In most species, cohesin is largely removed from the arms of the sister chromatids during prophase, allowing the individual sister chromatids to be resolved.
During which stage of mitosis does the nuclear envelope disappear and the chromatin is readily visible?
Explanation: Mitosis involves four distinct stages: prophase, metaphase, anaphase, and telophase. Prophase is the first step of mitosis, during which chromosomes condense and the nuclear envelope dissolves.
During which stage does the nuclear envelope dissolve chromosomes condense and the centrioles migrate to the poles?
Prophase. The first and longest phase of mitosis is prophase (Figure below). During prophase, chromatin condenses into chromosomes, and the nuclear envelope, or membrane, breaks down. In animal cells, the centrioles near the nucleus begin to separate and move to opposite poles (sides) of the cell.
|
