bacterial - Bacterial Genetics Prokaryote Basics The...

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Bacterial Genetics
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Prokaryote Basics The largest and most obvious division of living organisms is into prokaryotes vs. eukaryotes. Eukaryotes are defined as having their genetic material enclosed in a membrane-bound nucleus, separate from the cytoplasm. In addition, eukaryotes have other membrane-bound organelles such as mitochondria, lysosomes, and endoplasmic reticulum. almost all multicellular organisms are eukaryotes. In contrast, the genome of prokaryotes is not in a separate compartment: it is located in the cytoplasm (although sometimes confined to a particular region called a “nucleoid”). Prokaryotes contain no membrane- bound organelles; their only membrane is the membrane that separates the cell form the outside world. Nearly all prokaryotes are unicellular.
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Three Domains of Life
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Prokaryote vs. Eukaryote Genetics Prokaryotes are haploid, and they contain a single circular chromosome. In addition, prokaryotes often contain small circular DNA molecules called “plasmids”, that confer useful properties such as drug resistance. Only circular DNA molecules in prokaryotes can replicate. In contrast, eukaryotes are often diploid, and eukaryotes have linear chromosomes, usually more than 1. In eukaryotes, transcription of genes in RNA occurs in the nucleus, and translation of that RNA into protein occurs in the cytoplasm. The two processes are separated from each other. In prokaryotes, translation is coupled to transcription: translation of the new RNA molecule starts before transcription is finished.
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Bacterial Culture Surprisingly, many, perhaps even most, of the bacteria on Earth cannot be grown in the laboratory today. Bacteria need a set of specific nutrients, the correct amount of oxygen, and a proper temperature to grow. The common gut bacterium Escherichia coli (E. coli) grows easily on partially digested extracts made from yeast and animal products, at 37 degrees in a normal atmosphere. These simple growth conditions have made E. coli a favorite lab organism, which is used as a model for other bacteria.
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More Culture Bacteria are generally grown in either of 2 ways: on solid media as individual colonies, or in liquid culture. The nutrient broth for liquid culture allows rapid growth up to a maximum density. Liquid culture is easy and cheap. Solid media use the same nutrient broth as liquid culture, solidifying it with agar. Agar a polysaccharide derived from seaweed that most bacteria can’t digest. The purpose of growth on solid media is to isolate individual bacterial cells, then grow each cell up into a colony. This is the standard way to create a pure culture of bacteria. All cells of a colony are closely related to the original cell that started the colony, with only a small amount of genetic variation possible.
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