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Chapter 11 The Cell Cycle

Chapter 11 The Cell Cycle - Chapter 11 The Cell Cycle...

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Chapter 11 The Cell Cycle Chapter 11: The Cell Cycle Rudolf Virchow proposed that new cells arise through division of preexisting cells – cell division Chromosomes – carriers of hereditary material There are two types of cell division: meiosis and mitosis ( Figure 11.1 ). Meiosis is a division of the genetic material in the nucleus to produce daughter cells with one-half the amount of hereditary material found in the parent cell. Meiosis is involved only in the production of gametes (eggs and sperm); it is the basis of sexual reproduction and genetic inheritance. Mitosis is a division of the genetic material in the nucleus that produces daughter cells genetically identical to the parent cell. Mitosis is the basis of asexual reproduction and is involved only in the production of somatic (body) cells . Mitosis is usually accompanied by cytokinesis (“cell movement”) – division of the cytoplasm into 2 daughter cells. Mitosis, followed by cytokinesis, supplies the cells required for several key activities in eukaryotes – wound repair, reproduction, and growth. 11.1 Mitosis and the Cell Cycle Chromosomes contain a long double helix of deoxyribonucleic acid (DNA) wrapped around proteins. DNA carries the cell’s genetic information. The purpose of mitosis is to distribute this genetic material to daughter cells evenly. Prior to mitosis, each chromosome is copied. During mitosis, one of the copies is distributed to each of two daughter cells. The Cell Cycle Growing eukaryotic cells alternate between a dividing phase known as the mitotic or M phase and interphase , when no division occurs. This alternation is called the cell cycle . Cells spend most of their time in interphase. No dramatic changes are observed in the nucleus during interphase, when chromosomes are uncoiled into extremely long, thin structures. The cell cycle is the orderly sequence of events that occurs from the formation of a eukaryotic cell, through the duplication of its chromosomes, to the time it undergoes division itself. Two key cell-cycle events are the replication of the hereditary material and the separation of the copied chromosomes into two daughter cells. The hereditary material is duplicated, with one copy going to each daughter cell during mitosis. Result: daughter cells contain genetic information that is identical to that of the parent cell. When Does Chromosome Replication Occur? Chromosome replication occurs only during interphase and not during M phase ( Figure 11.3 ). The stage of the cell cycle during which DNA synthesis occurs is called the S phase . Question not answered until 1950s, with 2 teachnical innovations: ability to grow eukaryotic cells outside the source organism, in culture. 2) availability of radioactively
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labeled deoxyribonucleotides – building blocks of DNA. If they are present as DNA is being synthesized, they will be incorporated into the new DNA molecule and label it.
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