people like to say, as if it were obvious, that life is hard to define. this is misleading. life has properties that clearly distinguish it from everything else.
firstly, every living thing is cellular. in other words, it is either a single-celled creature or a creature composed of biological cells. every cell is bounded by its own outer membrane and contains a full set of instructions necessary for its operation and reproduction. furthermore, every cell uses the same operating system: "DNA makes RNA makes protein". DNA is a long complex molecule that contains the cell's instructions. it is transcribed into RNA, another long complex molecule similar to DNA; and then the RNA transcript is translated into protein. there are hundreds of billions of different proteins used by living things, but all of them are made from the same twenty amino acids, the "building blocks of life."
firstly, every living thing is cellular. in other words, it is either a single-celled creature or a creature composed of biological cells. every cell is bounded by its own outer membrane and contains a full set of instructions necessary for its operation and reproduction. furthermore, every cell uses the same operating system: "DNA makes RNA makes protein". DNA is a long complex molecule that contains the cell's instructions. it is transcribed into RNA, another long complex molecule similar to DNA; and then the RNA transcript is translated into protein. there are hundreds of billions of different proteins used by living things, but all of them are made from the same twenty amino acids, the "building blocks of life."
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