The Cell Cycle, Cellular Growth, and Cancer
- The G in G1 and G2 stands for gap, but it is also useful to think of it as G for growth, since these gap periods are where the cell grows, replicates its organelles and makes the proteins needed for DNA replication and cell division.
- Remember that S phase stands for synthesis. It is when the cell synthesizes (or copies/replicates) it is DNA.
- It is easy to think that M phase and mitosis are the same thing. But, in some special cases, mitosis can occur separately from cytokinesis. What is the result? A single cell with multiple nuclei.
Mitosis vs. Meiosis
- Remember the root for meiosis—"meio-"—means lessen, diminish. This makes perfect sense, because meiosis decreases the number of a cell's chromosomes by half. The types of chromosomes present are still the same though.
- Are you confused about why cells need to carry out meiosis? Just think what would happen if sperm and eggs where diploid. Every time they came together, they would form an organism with twice the number of chromosomes. You'd end up with twice as much DNA as your parents. Now plants can get away with these types of shenanigans, but animals (including humans) can't.
- Remember that a diploid cell has 2 times the number of chromosomes as a haploid cell. This makes sense because the cell has a copy of each chromosome from both of your parents.
- Sometimes it is confusing to figure out how much DNA there is in a cell. Remember that a diploid cell has 2 times the number of chromosomes as a haploid cell, therefore twice as much DNA. After DNA replication, it would have 4 times the genetic material of a haploid cell in G1.
- Chromosome vs. chromatid. A chromosome is a general term that describes the structure that contains the DNA of an organism. In contrast, a chromatid is a more specific term that refers to the individual copies of the DNA molecule in a particular chromosome. We call identical copies, formed after DNA replication, sister chromatids.
- Mitotic vs. Meiotic. Mitotic refers to mitosis, and meiotic refers to meiosis. Remember that the mitotic has two Ts—an extra T because of the T in mitosis.
- When you are trying to remember where things are moving to during cell division, think of the cell like a globe. Okay, it doesn't have all the different countries of the world printed on it, although that would be quite pretty, but it does have poles at the top and bottom, and an equator round the middle
- Remember that the "I" after the different stages (metaphase, anaphase, prophase, and so on) stands for that stage during meiosis I (or II if its meiosis II). If no number is presented, then you can assume that we are referring to that stage of the cell cycle in mitosis.
- It is helpful to think about the word recombine when you are trying to remember what recombination means. If you combine things, you are mixing them; if you recombine, you are remixing. In this case, you are remixing chromosomes, and the result is a chromosome that is part Mom and part Dad, or recombined.
- The cells at the end of meiosis I have only one homologous chromosome, and therefore, they are considered to be haploid. Try not to get confused by the fact that it still has as much DNA as a diploid G1 cell. (Meiosis I = one of each chromosome with 2 chromatids; diploid cell at G1 = two of each chromosome, but with only 1 chromatid)
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