mtDNA exists in one place as a large network ofinterlockingminicircles and maxicircles.Large network of 10-25,000 minicircles 0.5-2.5kb in lengthinterlocked with50-100maxicircles21-31kblong.(b)MinicirclesMaxicirclesKinetoplast16-11Fig.14.4
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-11 Fig. 14.4 mtDNA exists in one place as a large network of interlocking exists in one place as a large network of interlocking minicircles minicircles and maxicircles maxicircles. Large network of 10 Large network of 10-25,000 minicircles minicircles 0.5 – 2.5 kb in length 2.5 kb in length interlocked with 50 interlocked with 50-100 maxicircles maxicircles 21-31 kb long. 31 kb long
Maxicircles containgenes.Maxicircle DNAs carry only short, recognizable gene fragmentsinstead of wholegenes.Two types of RNAs in kinetoplast: short fragments and maturemRNAs.Minicircles carry no genes, involved in RNA editing.Minicircles(b)MaxicirclesKinetoplast16-12Fig.14.4
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-12 Maxicircles Maxicircles contain genes. contain genes. Maxicircle Maxicircle DNAs carry only short, recognizable gene fragments carry only short, recognizable gene fragments instead of whole genes. instead of whole genes. Two types of Two types of RNAs in kinetoplast kinetoplast: short fragments and mature : short fragments and mature mRNAs. Minicircles Minicircles carry no genes, involved in RNA editing. carry no genes, involved in RNA editing. Fig. 14.4
RNA editing,a rare variation on the basic themeofgeneexpressionRNA editing-A post-transcriptional modification process thatconverts pre-mRNA to mature mRNA by adding or deletingnucleotidesDiscovered in the mitochondria of trypanosomes, also found inthe mitochondria of some plants and fungiAdds or deletes uracils in trypanosomes.Addsordeletescytosinesinplants.16-13
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-13 RNA editing RNA editing, a rare variation on the basic theme , a rare variation on the basic theme of gene expression of gene expression RNA editing RNA editing – A post-transcriptional modification process that transcriptional modification process that converts pre converts pre-mRNA to mature mRNA by adding or deleting mRNA to mature mRNA by adding or deleting nucleotides. nucleotides. Discovered in the mitochondria of trypanosomes, also found in Discovered in the mitochondria of trypanosomes, also found in the mitochondria of some plants and fungi. the mitochondria of some plants and fungi. Adds or deletes uracils in trypanosomes. Adds or deletes cytosines in plants
RNA editing in trypanosomes: addition or deletion of uracilPre-mRNA pairs with guide RNA.(atypical G-U pairing)Unpaired G and A in guide RNA initiate the addition of U in pre-mRNA.Unpaired U's inpre-mRNAare deleted5'3'pre-mRNAGGGAAAGUUGUUG-UbaseG-U-Watson-CrickbasepairingG-Ubasebase pairingspairingpairing3'5'Guide RNAUGACAGUUUUAGACU16-14Fig.14.5
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-14 RNA editing in trypanosomes: addition or deletion of RNA editing in trypanosomes: addition or deletion of uracil Fig. 14.5 Pre-mRNA pairs with guide RNA. (atypical G-U pairing) Unpaired G and A in guide RNA initiate the addition of U in premRNA. Unpaired U’s in pre-mRNA are deleted
mRNA translation in mitochondriaMitochondria has its own translational machinerytRNASRibosomes: different from bacterial and eukaryotic ribosomes.Translation initiation,elongationfactorsMitochondrial translation resembles prokaryotic translationFirstamino acidisN-formylmethionine.Inhibited by bacterial translation inhibitors,such as chloramphenicolanderythromycin.16-15
Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 16-15 mRNA translation in mitochondria mRNA translation in mitochondria Mitochondria has its own translational machinery. tRNAs Ribosomes: different from bacterial and eukaryotic ribosomes. Translation initiation, elongation factors. Mitochondrial translation resem Mitochondrial translation resembles prokaryotic translation bles prokaryotic translation. First amino acid is N-formyl methionine. Inhibited by bacterial translation inhibitors, such as chloramphenicol and erythromycin