Cell Biology Facts
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According to Cell Theory, cells are the basic unit of all living things, cells are the basic functional and structural unit of all living things, and cells are always made from preexisting cells. By studying and examining cells, we gain an understanding for how our bodies, and the bodies of other organisms work.
Much of a cell's lifetime, called the cell cycle, is spent undergoing cell growth, making proteins, sugars, and fats, and assembling genetic material. This time in a the cell cycle is called interphase.
At the beginning of interphase, the G1 phase, a cell grows. It is during the G1 phase that cells synthesis, make, new proteins and organelles. This, the G1 phase, is the time when DNA are busiest, when the cell uses its DNA's blueprint of protein structure to make enzymes need to run basic systems in cells, to make actin and myosin for muscle contraction, and all of the proteins needed for like.
After the G1 phase, the cell enters the S phase. During the S phase, the cell is preparing for cell division, mitosis, by replicating its DNA. A cell's DNA contains the blueprints for how build every protein that it needs. A cell's DNA also contains an alarm clock, telling the cell when certain cellular events begin, such as when to stop growing, and start replicating DNA.
After the S phase, the cell begins its preparations for mitosis. This is the G2 phase, the shortest phase in the cell cycle. During the G2 phase, the cell makes those organelles and molecules, like the centrioles, that are specifically needed for mitosis.
At the end of the cell cycle, the cell begins mitosis. I will discuss mitosis in detail in a later section. For now, I will just state that mitosis is the phase when a cell splits, dividing into two new daughter cells. This is how new skin cells, new blood cells, and new muscle cells are produced.
What I described about applies only to eukaryotic cells. Eukaryotic cells are cells that contain a nucleus, and other well-defined, membrane bound organelles. Bacteria lack organelles, so they are placed in a group called prokaryotes.
Prokaryotes are generally smaller and simpler than eukaryotes. Prokaryotes only have cell membranes and cytoplasm. Its genetic material is not contained in a nucleus, or any other type of membrane-bound organelle. Still, as simple as they are, prokaryotes are very important in ecosystems. They serve in symbiotic relationships in many animals, particularly the group of herbivores call ruminants (e.g. cows). In ruminants, prokaryotes help digest cellulose. Ruminants lack the enzymes for breaking down cellulose into glucose.