Cells are the building blocks of life, because all organisms are made up of cells. Any introduction to biology course, such as this overview offered by Udemy, will include at least one unit on cells and the cell lifecycle. An important part of the cell lifecycle is meiosis or mitosis, depending on the cell. Meiosis and mitosis are similar stages in the lifecycle, but they have an important distinction. Meiosis only occurs in gamete, or sex cells, while mitosis occurs in all other cells. By understanding the different phases, as well as the distinctions between the two, you will have a strong foundation to learn more about the life cycle of cells and the effect on human biology. The study of biology has a profound effect on human life, encompassing everything from understanding health and disease to genetics to the environment.
What is Mitosis?
Mitosis is the cycle that eukaryotic cells go through in order to divide. During mitosis, a cell duplicates its DNA and divides into two genetically identical cells. Mitosis is typically followed by cytokinesis, which divides the other properties of the cell including cytoplasm, organelles and the cell membrane. Karyokinesis also occurs, which divides the nucleus. Mitosis and cytokinesis are part of the mitotic phase of the cell cycle, which make up about 20 percent of the entire lifecycle of a cell. The end result of mitosis is two completely separate cells with equal and similar cellular components.
The Stages of Mitosis
Students often struggle to remember the phases of mitosis when studying for Biology exams such as the GSCE, in addition to chapter tests, midterms, and finals. The stages of mitosis include prophase, prometaphase, metaphase, anaphase, and telophase. Each phase has a distinct role in the overall cell division process. Prior to mitosis, the chromosomes are copied, and each copy is known as a chromatid, bound together by a centromere. These two identical chromatids are called sister chromatids. The duplication of DNA does not actually occur during mitosis; instead, it occurs during the S phase of interphase.
The initial phase of mitosis is prophase. In this stage, the membrane around the nucleus begins to dissolve and the chromatin (the genetic material in the nucleus that is normally loosely bundled in a coil) condenses into discrete chromosomes. At this stage, the chromosomes become visible under high magnification. In prometaphase, the nuclear membrane disintegrates and the two kinetochores are formed at the centromere, attached to the chromatid. The centromeres will work to separate the sister chromatids.
Then, the cell moves into metaphase, where the chromosomes align in the equator and the centromeres move to the poles to prepare for separation. After this, anaphase occurs, which is when the chromosome pairs separate, being pulled by the centromeres, finishing when the proteins that bind the chromatids together are cleaved. Now the chromosome pairs are at opposite ends of the cells. During telophase, clean up occurs and the cell begins to elongate. The new nuclear membrane forms around the new set of chromosomes. Mitosis is complete, and moves into cytokinese, where the rest of the cell divides.
What is Meiosis?
Meiosis is the special cell division cycle for gamete cells, or sex cells. Chromosomes carry the genetic code for an organism, and come in pairs. In asexual reproduction, a cell will just divide itself to create two new cells. However, for sexual reproduction, gamete cells are necessary. In sexual reproduction, the parent provides one set of each chromosome, or half the genetic code for an organism. When the two parent donor gametes – typically an egg and sperm – meet in fertilization, they provide the offspring with the full set of necessary chromosomes. For example, humans require 46 chromosomes, or 23 pairs. An egg or sperm will have just 23 chromosomes, or one half of the pair. This makes gamete cell division more complex than ordinary cell division. Within this cycle, the number of chromosomes is halved, typically going from a diploid (two sets) to haploid (one set) cell. It also includes a step where the chromosomes cross, allowing for more genetic diversity in reproduction.
The Stages of Meiosis
Meiosis has two stages: meiosis I and meiosis II. The cells are divided during both stages. These stages are similar to the mitosis stages. Just like mitosis, prior to meiosis, each chromosome’s DNA is replicated during the S phase. During meiosis, the parent cell begins with the full set of chromosome pairs, so in humans it will be 46. During the S phase, the number of chromosomes double, so each cell will have two copies of each chromosome, similar to mitosis. However, soon the differences between the two begin to emerge. The basic process of meiosis begins when the homologous, or the copies of each chromosome, exchange genetic material, which is known as crossing over, in order to provide genetic diversity. After this, the pairs separate as two cells are formed, each with one set of chromosomes. Then, the chromosomes split into two again to form to haploid cells that include just one set of chromosomes. At the end of meiosis, four genetically distinct haploid cells are produced, which then will mature into gametes.
The phases of meiosis have similar names to that of mitosis. Meiosis I, in a process very similar to mitosis, begins with prophase I, which is when the chromosome crossover occurs. The cell then moves into metaphase I, which is when the chromosomes line up in the equatorial plane in preparation for separation. The next stage is anaphase I, which is when the chromosomes are separated and the cell begins to elongate to divide. Telophase I is when the division completes, which each cell having a complete set of chromosome pairs. Now, it is time for meiosis II. The mechanical process is the same, but it ends with four haploid cells rather than two regular cells. The phases are prophase II, metaphase II, anaphase II and telophase II. The chromosomes do not duplicate, so when the chromosome pairs are separated during the phases, there is only one half rather than a complete pair.
What is the Difference Between Meiosis and Mitosis?
The main difference between meiosis and mitosis is the type of cells that undergo the process. Mitosis occurs in all eukaryote cells, while meiosis is a special type of mitosis that only occurs in gamete, or sex, cells. Mitosis creates two identical cells from one mother cell. Meiosis creates four genetically unique haploid cells from the mother cell. The stages that occur during mitosis and meiosis are similar; it is just that during meiosis the cells go through two cycles. A common essay in biology is describing the difference between the mitosis and meiosis. Writing a biology paper can be difficult, but Udemy’s A+ Research Paper in Biology course will help you know how to write a stellar paper.
Learn More about Cell Biology Today
Knowing about the life cycle of cells is an important part of biology. Each cell has the genetic code that controls the different body processes, such as metabolism, immune defense, and even the neural processes. Understanding cell biology creates a foundation to then learn more about the science of the human body, including nutrition and exercise science, which you can learn more about with this great Udemy course. Meiosis and mitosis also explain how the DNA in cells can change and cause disease, such as cancer. Now that you know the difference between mitosis and meiosis, you can continue your biology education and learn even more about how cells are the building blocks of life.