TABLE16.3VariationsintheGeneticCodeofHumanMitochondriaAlteredgeneticcodeUniversal CodeCharacteristicmtDNA Codein mitochondria3222NumberoftRNAsshows that theUGGTrpTrpUGAStopTrpgenetic code is notAGGArgStopuniversalAGAArgStopAUGMetMetlleAUAMetAlteredgeneticcode.ThehumanmtDNAgeneticcodeissimplifiedsuchthatamodifiedUinthetRNA"wobble"positioncanreadallfourcodonsinacodonfamily(thatis,UUU,UUC,UUA,andUUG).AnunmodifiedUcanreadbothpurines,andGcanreadbothpyrimidines.Tryptophan tRNA hasa Uin the wobbleposition,soit will readboththetraditional UGGcodonandtheassociatedUGAstopcodonastryptophan.Similarly,the methionine codon reads bothAUG and theassociated AUAasmethionine.Finally,humanmtDNAhasonlyasinglearginine tRNA such that two of the sixarginine codons (AGGand AGA)nowfunctionasstopcodons16-16
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-16 Altered genetic code Altered genetic code in mitochondria in mitochondria shows that the shows that the genetic code is not genetic code is not universal universal
14.2 Chloroplasts and their genomesChloroplasts（叶绿体）are sitesofphotosynthesisFound in plants and algae40-50chloroplasts eachleaf cellincorn.Chloroplastsinamoss16-17Fig.14.6
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-17 Chloroplasts Chloroplasts (叶绿体) are sites of photosynthesis. are sites of photosynthesis. Found in plants and algae. 40 50 chloroplasts each leaf cell in corn. 14.2 Chloroplasts and their genomes Chloroplasts in a moss Fig. 14.6