1/6/2024 0 Comments Steps of prophaseBritannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.For the claymation I used a phone camera resting face down on a glass coffee table over the models.Įnter your email address to receive notifications of new posts by email. Modelling clay is a great medium for demonstrating and thinking about how things work, move and change. The modelling clay images above are from my claymation showing mitosis. Of course, the cell is also full of other organelles that have to be shared between the new cells. Chromosome banding helps recognise the chromosomes and identify any changes when an abnormality is suspected. Cytogeneticists (chromosome scientists) use this technique to get enough metaphase chromosomes for analysis. If a chemical that destroys the microtubules is added to a laboratory culture, the chromosomes are stopped at metaphase. Cytokinesis finishes and we have two new cells in interphase. The cell membrane (the outer covering) pinches at the centre ( cytokinesis). The chromosomes start to uncoil to form the two new daughter nuclei – telophase. At anaphase the two chromatids (half chromosomes) become the new chromosomes as they separate and move in opposite directions along the microtubules. They are attached by their centromeres to microtubules which stretch across the cell. Metaphase – the chromosomes line up in the centre of the cell at the metaphase plate. Then as the cell divides to become two daughter cells, the two halves of the centromere split and travel along the microtubules in opposite directions, pulling the two halves of the chromosome behind them. When the cell is ready to divide each chromosome has two chromatids or identical halves, joined at the centromere.Īt metaphase the chromosomes meet in the middle of the cell at the metaphase plate. The DNA folds up further to make recognisable chromosomes. The DNA in the nucleus starts to coil up in a pre-determined order and take shape as prophase chromosomes. (Actually it seems that the chromosomes stay in relatively distinct domains – but under the microscope they appear as one entity.) The DNA in the interphase nucleus copies itself as the cell grows. The DNA from all the chromosomes, intermingled with each other, is represented by grey modelling clay. Now follow the captions under the pictures. You could add prometaphase: the part of prophase between the nuclear membrane breaking down and metaphase (where the chromosomes line up at the metaphase plate). Mitosis is broken up into a series of phases: interphase, prophase, metaphase, anaphase, telophase. The two halves of each chromosome are copies of each other. Human metaphase chromosomes stained with Giemsa (unbanded). The problem of how to distribute the copied chromosomes evenly to the two “daughter cells” is handled very elegantly. For our bodies to grow, these cells need to make copies of themselves. The genes are strung together along the chromosome, and each cell has a set of chromosomes. A gene is made of a certain sequence of DNA letters (or bases) and spells out an instruction for a step in the complex workings of our bodies (such as the structure of insulin). It’s so small that we can’t see it without a microscope, but it goes on in our bodies billions of times a day.ĭNA is a very long molecule made up of the genetic alphabet (which has four letters: A, C, G, T). It’s a choreographed dance of the chromosomes. Mitosis has to be one of the more beautiful things in nature.
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