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2: Symbiogenesis and the Plant Cell
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2.1: Introduction to Cells
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In 1838, Schleidern and Schwann stated that (1) all plants and animals are composed of cells and that (2) cell is the most basic unit (“atom”) of life. In 1858, Virchow stated that (3) all cells arise by reproduction from previous cells (“Omnis cellula e cellula” in Latin). These three statements became the base of the cell theory. Discovery of cells is tightly connected with the development of microscopy.
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2.2: Mitochondria and Chloroplasts
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To escape from competition, cells which were prokaryotic became larger. To facilitate communication between all parts of this larger cell, they developed cytoplasm mobility using actin protein. In turn, this mobility resulted in acquiring phagocytosis, which is when a large cell changes shape and can engulf (“eat”) other cells. This way, cells that used to be prey became predators. These predators captured prey by phagocytosis and digested bacteria in lysosomes, which use enzymes that destroy th
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2.3: Cell wall, Vacuoles, and Plasmodesmata
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Plant cells do not have well-developed internal cytoskeleton, but cell wall provides an external one. There are two kinds (or, better, two stages of development) of cell walls, the primary and the secondary. The primary cell wall is typically flexible, frequently thin and is made of cellulose, different carbohydrates and proteins. The secondary cell wall contains also lignin and highly hydrophobic suberin. These chemicals completely block the exchange between the cell and the environment.
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2.4: Other Parts of the Cell
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The central dogma of molecular biology states that DNA will be converted into RNA by a process called transcription and RNA will be converted to protein by a process called translation. Translation in non-reversible whereas transcription could be reverted: there are viruses, such as HIV, that can make DNA from RNA with the enzyme called reverse transcriptase. The nuclear envelope is built from a double-layered membrane.