HeLa cell mitochondria

The discovery that DNA forms catenanes and knots, some of them extremely complex, initiated a new field of research which has been called Biochemical Topology [21]. In 1967, Vinograd and co-workers detected in HeLa cell mitochondria isolable DNA molecules that consist of independent, double-stranded, closed circles that are topologically interlocked or catenated like the links in a chain [22, 23]. A few years later, catenanes had been observed everywhere that circular DNA molecules were known [24] and the first knot was found by Liu and coworkers in single-stranded circular phage fd DNA treated with Escherichia coli co-protein [25]. In 1980, knots could also be generated in double-stranded circular DNA [26]. 

MukhopadhyayA,Ni L, Weiner H (2004) A co-translational model to explain the in vivo import of proteins into HeLa cell mitochondria. Biochem J 382 385-92 Mus MM, Moczydlowska M (2000) Internal morphology and taphonomic history of the Neoproterozoic vase-shaped microfossils from the VisingsO Group, Sweden. Norsk Geol Tidsskr 80 213-228... 

The HeLa cells originally were transformed by the HPV-encoded oncoproteins (that neutralize p53 and Rb cellular mmor suppressor genes). Distinction between self and non-self probably did not exist when ancient chimeric cells were formed, and engulfed bacteria were accepted as self (proteobacteria for the mitochondrion cyanobacteria for the chloroplast). Malignantly transformed cells appear to be impervious, as to the distinction between self and non-self, when it comes to... 

Yeast mitochondrial DNA occurs as double-stranded 26-/im closed circles, a molecular size corresponding to about 50 x 10 daltons. The number of circles per mitochondrion may range from zero to about five the total amount of cellular mtDNA per wild-type cell varies with the strain and accounts for 10-25% of the total cellular DNA. RNA-DNA hybridization studies indicate that yeast mtDNA contains one cistron of each of the 15 S and 21 S RNA species and probably 20 tRNA cis-trons. It has been reported that mitochondria from HeLa cells contain only 12 tRNA cistrons, 9 on the heavy DNA strand and 3 on the light strand. These authors suggested that since the proteins formed by mitochondrial ribosomes are enriched in hydrophobic amino acids, an array of 12 tRNAs may be sufficient for the complete synthesis of the inner-membrane proteins by mitochondria. Alternatively, some nuclear coded tRNAs may be available to the mitochondrial protein-synthesizing system. 

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