Yeast cells mitochondria

Mitochondria are present in all eukaryotic cells that use oxygen in respiration, but the number per cell and the form and size vary.1-4 Certain tiny trypanosomes have just one mitochondrion but some oocytes have as many as 3 x 105. Mammalian cells typically contain several hundred mitochondria and liver cells5 more than 1000. Mammalian sperm cells may contain 50-75 mitochondria,6 but in some organisms only one very large helical mitochondrion, formed by the fusion of many individual mitochondria, wraps around the base of the tail. Typical mitochondria appear to be about the size of cells of E. coli. However, study of ultrathin serial sections of a single yeast cell by electron microscopy has shown that, under some growth conditions, all of the mitochondria are interconnected.7... 

In anaerobic conditions, cells can metabolize pyruvate to lactate or to ethanol plus CO2 (in the case of yeast), with the reoxidation of NADH. In aerobic conditions, pyruvate is transported into the mitochondrion, where pyruvate dehydrogenase converts it into acetyl CoA and CO2 (see Figure 8-5). 

Fig. 16.2 Diagram of an electron micrograph of a section through a resting cell of bakers yeast Saccharomyces certvisiae). ER, endoplasmic reticulum M, mitochondrion N, nucleus Nm, nuclear membrane Nn, nucleolus Pi, invagination PI, plasmalemma V, vacuole Vp, polymetaphosphate granule W, cell wall Ws, bud scar L, lipid granule (sphaerosome).

Hoffmann, H.P., Avers, C.J. Mitochondrion of yeast Ultrastructural evidence for one giant, branched organelle per cell. Science 181, 749-751 (1973)... 

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. 

---