All organisms need to grow and this means that new cells are required to replace old ones. For human kids, the new cells allow us to have stronger bones, heal cuts and bruises, and even become taller.
We can do this through a process called “mitosis” in which the original cell (parent) divides to create 2 new cells (daughters).
The 2 new daughter cells are identical to the parent, including identical chromosomes.
Cells need to be constantly replaced and there are three ways that they do this: mitosis which is asexual reproduction, where only one parent is involved, and meiosis, which is sexual reproduction with two parents; and binary fission that is used by simple organisms such as bacteria.
When a cell is preparing for mitosis it goes through a process called “interphase.” It will then go through six additional phases for mitosis to be completed: prophase, prometaphase, metaphase, anaphase, and telophase with cytokinesis. This is referred to as the “cell cycle.”
The interphase portion of the cell cycle takes up around 80% of the cell’s life. During this time the cell is doing its job while also preparing for the process of mitosis.
Interphase can be broken up into three sub-phases called G1, S, and G2.
- G1 is the “gap phase” that lets the cell size get bigger while also giving it the chance to prepare by copying its own organelles as well as start the process of protein making that it will need for DNA building.
- The synthesis phase or “S phase” is the moment that the cell knows to copy its DNA that is in the nucleus. Another signal goes out to copy the centrosome which is the organelle that is responsible for keeping the microtubules organized and helps to separate the DNA for the new cells that will be created.
- The final portion of interphase is the second gap phase, or “G2.” By this time the cell is making more proteins and organelles and is growing bigger and bigger. G2 also starts to reorganize the various parts so that it can start mitosis.
From this point on mitosis becomes more active and complex. This is the first official stage of mitosis and by this point the cell has done a lot of work to prepare.
It already has a DNA copy and the nucleus chromosomes each have two “sister chromatids” which are connected copies. The S phase took care of making two centrosomes. Prophase has three main actions:
- The chromosomes prepare for division by altering their condition into tight coils from their previous long strings. The chromosomes will be easiest to divide when they are smaller.
- The mitotic spindle is required to separate the chromosomes, so the cell starts to form the microtubules needed for the spindle. The mitotic spindle has its name because it looks like an old fashioned weaving spindle and even has string bunches between its two ends. It will push the 2 centrosomes apart as it continues to grow in between them.
- The nucleolus is that area responsible for making ribosomes and in the last portion of the prophase it will begin to break down.
- To prepare for cell division, the chromosomes complete their coiling process so that they are now compact and very small.
- At this point there is a final break down of the nuclear membrane so that the chromosomes can be released.
- Continued growth of the mitotic spindle allows it to catch the chromosomes that are escaping and you would see the nucleus completely break down.
- To catch the chromosomes the microtubules have to grab them at the location where the two sister chromatids are the closest to each other. This area is called the “kinetochores,” and a microtubule will attach itself to a sister pair of chromatids in one chromosome.
- You can kind of compare this phase to a sports team in the middle of a game. You would see the mitotic spindle catching all of the chromosomes and then the microtubules creating a single neat line called a “metaphase plate” in the center of the cell.
- Microtubules on the mitotic spindle ends will be doing their preparation by attaching to the kinetochore of one of the chromosomes in a sister pair of chromatids.
- Everything needs to be in complete order at this point. The cell confirms that all chromosomes are lined up perfectly, the spindle does a checkpoint, and microtubules all have to be correctly attached. If any of this isn’t done correctly, the cell won’t have an even division. A cell will refuse to divide if the metaphase plate doesn’t have the chromosomes lined up.
- This is the phase of action where there is a separation down the middle of the sister chromatids and the microtubules pull them apart to push them to the spindle’s opposite ends.
- To make the cell longer, any free microtubules will continue to push the spindle ends further apart.
Telophase and Cytokinesis
- The telophase gives the cell the chance to finish dividing and since the mitotic spindle isn’t needed anymore, it will break down.
- You see two nuclei, one that will be required for each chromosome set.
- The previously coiled chromosomes can now stretch and return to their longer state.
- The final stage of dividing into two new daughter cells is called “cytokinesis”. The walls of the cell pinch themselves off and there is a complete middle split. The daughter cells that are now in existence are identical to the parent cell and each has a complete chromosome set.
Fun Facts about Mitosis
- Once cytokinesis is done, the cell returns to interphase, to calmly wait until the next order is given for cell division.
- It can take 5-6 hours for the S Phase to complete.
- For most cells the G2 phase takes about 3-4 hours.
- The interphase process lasts between 18-20 hours.
- The time that the cell takes to prepare for mitosis process and the cell division completion is around 2 hours.
- There are four parts of the human body where mitosis occurs the most: your skin, your muscles, your DNA, and your circulatory system.
Interesting Facts about Biology
- Your immune system in your body is designed to protect you. However, sometimes the immune system can become confused and attack the good cells. An example of this is in Type 1 diabetes where the T cells begin attacking the cells that make insulin in your pancreas.
- Medications can be dangerous. Some medicines have been created to taste badly so that children won’t try to take too much.
- Scientists estimate that there are around 1.5 million different fungi species in the world.
- If you are a mycologist, you are a scientist that specializes in fungi study.
- You might be surprised to find out that the Trichoderma fungus is used in the process of creating stone-washed jeans.
- Protists are a very unusual group of organisms. They don’t fit into any of the other scientific groups. Many of the protists that have been identified can act as a “pathogen” (like a bacteria or virus) to delivering diseases to humans.
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