Phases of mitosis | Mitosis | Biology (article) | Khan Academy
During mitosis, chromosomes attach to a spindle of microtubules that distribute them Once mitosis is complete, the entire cell divides in two by way of the process called cytokinesis (Figure 1). . Figure 3: Mitosis: Overview of major phases. A summary of Telophase and Cytokinesis in 's Mitosis. In higher order plants, the cytokinesis process is slightly different because the cytoplasm splits with the. The difference between mitosis and meiosis is in the process by which In summary, the primary differences between meiosis and mitosis are.
Since the key measure of success for organisms is whether they replace themselves, and thus achieve persistence on the planet, the various means they use to do so become central to our thinking, but in order to think through the implications of complex life-cycles, and the forces acting upon organisms favouring variable balances between sexual and asexual reproduction, it is important to be clear from the start about the basic underlying processes: What you should know about the processes Theoretically, students entering Biology really ought to know almost every technical point about nuclear and cell division: In practice, though, I will not ask you to enumerate the stages or the details in an exam.Mitosis and Cytokinesis [HD Animation]
I will, however, proceed in lectures on the assumption that you are aware of the information, or at least that you will go and refresh your knowledge when necessary. For example, when we consider the phenomenon of independent assortment, it would be difficult for you to predict progeny ratios unless you understand the meiotic steps which cause chromosomes to align as they do in the two divisions.
Whatever the ploidy of the first nucleus, the daughter nuclei will be of the same ploidy. Always preceded by DNA replication. Daughter nuclei each inherit a quarter of the amount of DNA included in the original nucleus, usually one haploid set of single-stranded chromosomes derived randomly from the original diploid set of double-stranded ones.
First division preceded by DNA replication, the second division not. Delay between divisions may be lengthy or almost nonexistent. Daughter nuclei may all survive spores, sperm cellsor only some do most eggs. Involves division of the cytoplasm and included organelles, usually to send equal amounts to each daughter cell but sometimes highly unequal especially in egg production. May or may not occur between the meiotic divisions, and in most organisms except coenocytic forms does occur following mitosis and following the second meiotic division.
For instance, we might consider some or all of these puzzles: Growth — in some organisms, like plants and animals, growth of the body may involve making each cell larger, but more often involves making more cells by mitosis.
Large body-size confers many advantages on organisms that can achieve it, but also imposes costs: You could even propose that the repeated cell-division needed to grow a large body may make the body more prone to diseases of unmoderated division — cancers. Now in some organisms, like fungi, relatively large bodies with many nuclei are pretty much coenocytic rather than subdivided into cells or cell types. We often view the presence of distinct cell types, organized into tissues and organs, as a sign of efficiency, but fungi seem to be doing quite well!
Why should some organisms have mitosis with, and others more or less without, cytokinesis? How necessary is local specialization of body parts for a relatively large organism?
Difference Between Cytokinesis and Mitosis
We may not be able to answer these questions satisfactorily, but they could lead to other interesting hypotheses, and stretch our understanding of life usefully. The cases of multinucleate organisms, whether cellular one nucleus per cell or coenocytic, suggest that a single nucleus can control only a certain volume of cytoplasmic machinery. 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.
The great majority of the cell divisions that happen in your body involve mitosis. For single-celled eukaryotes like yeast, mitotic divisions are actually a form of reproduction, adding new individuals to the population.
Instead, they split up their duplicated chromosomes in a carefully organized series of steps. Phases of mitosis Mitosis consists of four basic phases: Some textbooks list five, breaking prophase into an early phase called prophase and a late phase called prometaphase. These phases occur in strict sequential order, and cytokinesis - the process of dividing the cell contents to make two new cells - starts in anaphase or telophase. You can remember the order of the phases with the famous mnemonic: The cell has two centrosomes, each with two centrioles, and the DNA has been copied.
At this stage, the DNA is surrounded by an intact nuclear membrane, and the nucleolus is present in the nucleus. This animal cell has also made a copy of its centrosome, an organelle that will play a key role in orchestrating mitosis, so there are two centrosomes. 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 grows between the centrosomes as they move apart.
The nucleolus or nucleoli, plurala part of the nucleus where ribosomes are made, disappears. This is a sign that the nucleus is getting ready to break down. The nuclear envelope breaks down and the chromosomes are fully condensed. In late prophase sometimes also called prometaphasethe 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.
Anatomy of the mitotic spindle. Diagram indicating kinetochore microtubules bound to kinetochores and the aster. The aster is an array of microtubules that radiates out from the centrosome towards the cell edge. Diagram also indicates the centromere region of a chromosome, the narrow "waist" where the two sister chromatids are most tightly connected, and the kinetochore, a pad of proteins found at the centromere.
Microtubules can bind to chromosomes at the kinetochore, a patch of protein found on the centromere of each sister chromatid. Centromeres are the regions of DNA where the sister chromatids are most tightly connected. Microtubules that bind a chromosome are called kinetochore microtubules. More microtubules extend from each centrosome towards the edge of the cell, forming a structure called the aster. 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.
Mitosis, meiosis, and cytokinesis
All the chromosomes align at the metaphase plate not a physical structure, just a term for the plane where the chromosomes line up. At this stage, the two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles. Before proceeding to anaphase, the cell will check to make sure that all the chromosomes are at the metaphase plate with their kinetochores correctly attached to microtubules.