Cell Division

Cell Division - Cell Division: I. Chromosomes: a. Often...

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Cell Division: I. Chromosomes: a. Often exist in pairs within cells, and when they are, the cell is said to be diploid. i. Humans have 23 pairs in each cell, with the exception of gametes. ii. Table 10.1 talks about other species’ and their numbers of chromosomes. iii. Chromosomes are made of chromatin, which is made of DNA and Protein. Usually around 40% DNA and 60% Protein. 1. Fig 10.5 shows how long DNA strands coil up into small chromosomes. 2. Histone proteins are the primary proteins involved in these shenanigans. a. DNA coils around Histones, which all repeat and coil up into chromosomes. 3. When a cell is not dividing, the DNA usually comes uncondensed for use. a. This is called euchromatin, which means that the genetic information is usable b. Some DNA will remain coiled and unusable, called heterochromatin. i. More heterochromatin exists in the centromere, so it heterochromatin may be a structural function. ii. It could also be fore gene regulation, keeping genes that are not currently needed out of use. iv. These pairs are called “homologous chromosomes”. Usually they are drawn side by side with the same size and same shape. 1. Center called centromere, and area on either side of center is called kinetochore, which is made of protein. a. Kinetochore is where microtubules attach to pull apart chromosomes. b. Material that holds chromatids together at the centromere is called “cohesin”, which is a protein. v. When cells are not diploid (chromosomes coming in pairs), they are called haploids. vi. Karyotype—a cell’s chromosome array. How the chromosomes are arranged. 1. This is significant because not all chromosomes look alike.
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II. Cell Cycle: a. Process of growth and cell division in which most cells engage. b. Different phases: i. Interphase 1. G 1 Gap Phase: a. There is also a G 0 phase that is a resting phase. Some cells never exit this phase. b. Stuff is produced in this phase. 2. S phase: Synthesis a. DNA is produced 3. G 2 : Gap 2 Phase: a. Lots of things are produced within the cell. Molecules are made and organelles are assembled. b. Microtubules are assembled into spindles to pull things apart. ii. M-Phase: 1. Mitosis (Fig 10.11): Division of one nucleus into 2 nuclei. Discovered in 1879 by Fleming, who was studying Salamanders. a.
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Cell Division - Cell Division: I. Chromosomes: a. Often...

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