300817 Lecture Notes - Lecture 12: Deoxyadenosine, Uridine, Thymidine
Document Summary
Prokaryotes rst came into existence and contain no self-contained nucleus, therefore making their mechanisms much simpler compared to the later- evolved eukaryotes, which do contain a nucleus enveloping the cell"s dna and nuclear organelles. Because viruses, viroids, prions and such depend entirely on the physiology of other cells (i. e. , cells containing their own physiology), the former entities are often not considered to be living by the biologists who study them. All living cells, whether prokaryotes or eukaryotes, contain the following distinguishing characteristics: Based on the properties shared by all independently living organisms on earth, The dna is composed of four nucleotides (deoxyadenosine, deoxycitidine, deoxtthydimine and de oxyguanosine), to the exclusion of other possible deoxynucleotides. The genetic code is composed of three-nucleotide codons, thus producing 64 different codons. Since only 20 amino acids are used, multiple codons code for the same amino acids. This structure is arbitrary and shared by all eukaryotes and prokaryotes.
